AI Trajectory

null

{
  "EnableConfigs": [
    "NUMA",
    "MIGRATION"
  ],
  "FocusSymbols": [
    "copy_mc_to_kernel_nt",
    "folio_mc_copy_nt"
  ],
  "Reasoning": "The patch introduces a new memory migration mode `MIGRATE_ASYNC_NON_TEMPORAL_STORES` which uses non-temporal stores for memory demotion on x86_64. This is reachable via page reclaim (`shrink_folio_list` -\u003e `demote_folio_list` -\u003e `migrate_pages`) when memory demotion is enabled. The new functions `copy_mc_to_kernel_nt` and `folio_mc_copy_nt` perform the actual copying and should be focused during fuzzing.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit b77301aee3a1dac3601dd685f20fa9adec71e06b\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sat Aug 1 04:39:47 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h\nindex 367297b188c39..2d0938d3e372c 100644\n--- a/arch/x86/include/asm/uaccess.h\n+++ b/arch/x86/include/asm/uaccess.h\n@@ -494,6 +494,10 @@ unsigned long __must_check\n copy_mc_to_kernel(void *to, const void *from, unsigned len);\n #define copy_mc_to_kernel copy_mc_to_kernel\n \n+unsigned long __must_check\n+copy_mc_to_kernel_nt(void *to, const void *from, unsigned len);\n+#define copy_mc_to_kernel_nt copy_mc_to_kernel_nt\n+\n unsigned long __must_check\n copy_mc_to_user(void __user *to, const void *from, unsigned len);\n #endif\ndiff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c\nindex 97e88e58567bf..5a2ee5c2211ed 100644\n--- a/arch/x86/lib/copy_mc.c\n+++ b/arch/x86/lib/copy_mc.c\n@@ -81,6 +81,32 @@ unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigne\n }\n EXPORT_SYMBOL_GPL(copy_mc_to_kernel);\n \n+/**\n+ * copy_mc_to_kernel_nt - memory copy that handles source exceptions\n+ * if enabled, otherwise uses non-temporal stores\n+ * @dst: destination address\n+ * @src: source address\n+ * @len: number of bytes to copy\n+ *\n+ * Return 0 for success, or number of bytes not copied if there was an\n+ * exception.\n+ */\n+unsigned long __must_check copy_mc_to_kernel_nt(void *dst, const void *src, unsigned len)\n+{\n+\tunsigned long ret;\n+\n+\tif (copy_mc_fragile_enabled) {\n+\t\tinstrument_memcpy_before(dst, src, len);\n+\t\tret = copy_mc_fragile(dst, src, len);\n+\t\tinstrument_memcpy_after(dst, src, len, ret);\n+\t\treturn ret;\n+\t}\n+\n+\tmemcpy_flushcache(dst, src, len);\n+\treturn 0;\n+}\n+EXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt);\n+\n unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, unsigned len)\n {\n \tunsigned long ret;\ndiff --git a/fs/nfs/write.c b/fs/nfs/write.c\nindex 1ed4b3590b1ac..beae4441e0805 100644\n--- a/fs/nfs/write.c\n+++ b/fs/nfs/write.c\n@@ -2119,7 +2119,7 @@ int nfs_migrate_folio(struct address_space *mapping, struct folio *dst,\n \t}\n \n \tif (folio_test_private_2(src)) { /* [DEPRECATED] */\n-\t\tif (mode == MIGRATE_ASYNC)\n+\t\tif (migrate_mode_is_async(mode))\n \t\t\treturn -EBUSY;\n \t\tfolio_wait_private_2(src);\n \t}\ndiff --git a/include/linux/highmem.h b/include/linux/highmem.h\nindex af03db851a1d9..a5cb435b9ffe1 100644\n--- a/include/linux/highmem.h\n+++ b/include/linux/highmem.h\n@@ -468,6 +468,32 @@ static inline int copy_mc_highpage(struct page *to, struct page *from)\n \n \treturn ret;\n }\n+\n+#ifdef copy_mc_to_kernel_nt\n+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n+{\n+\tunsigned long ret;\n+\tchar *vfrom, *vto;\n+\n+\tvfrom = kmap_local_page(from);\n+\tvto = kmap_local_page(to);\n+\tret = copy_mc_to_kernel_nt(vto, vfrom, PAGE_SIZE);\n+\tif (!ret)\n+\t\tkmsan_copy_page_meta(to, from);\n+\tkunmap_local(vto);\n+\tkunmap_local(vfrom);\n+\n+\tif (ret)\n+\t\tmemory_failure_queue(page_to_pfn(from), 0);\n+\n+\treturn ret;\n+}\n+#else\n+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n+{\n+\treturn copy_mc_highpage(to, from);\n+}\n+#endif\n #else\n static inline int copy_mc_user_highpage(struct page *to, struct page *from,\n \t\t\t\t\tunsigned long vaddr, struct vm_area_struct *vma)\n@@ -481,6 +507,12 @@ static inline int copy_mc_highpage(struct page *to, struct page *from)\n \tcopy_highpage(to, from);\n \treturn 0;\n }\n+\n+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n+{\n+\tcopy_highpage(to, from);\n+\treturn 0;\n+}\n #endif\n \n static inline void memcpy_page(struct page *dst_page, size_t dst_off,\ndiff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h\nindex 265c4328b36ad..f7186e705b487 100644\n--- a/include/linux/migrate_mode.h\n+++ b/include/linux/migrate_mode.h\n@@ -3,6 +3,8 @@\n #define MIGRATE_MODE_H_INCLUDED\n /*\n  * MIGRATE_ASYNC means never block\n+ * MIGRATE_ASYNC_NON_TEMPORAL_STORES means never block and use non-temporal\n+ * stores if supported by the architecture\n  * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking\n  *\ton most operations but not -\u003ewritepage as the potential stall time\n  *\tis too significant\n@@ -10,10 +12,17 @@\n  */\n enum migrate_mode {\n \tMIGRATE_ASYNC,\n+\tMIGRATE_ASYNC_NON_TEMPORAL_STORES,\n \tMIGRATE_SYNC_LIGHT,\n \tMIGRATE_SYNC,\n };\n \n+static inline bool migrate_mode_is_async(enum migrate_mode mode)\n+{\n+\treturn mode == MIGRATE_ASYNC ||\n+\t\tmode == MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n+}\n+\n enum migrate_reason {\n \tMR_COMPACTION,\n \tMR_MEMORY_FAILURE,\ndiff --git a/include/linux/mm.h b/include/linux/mm.h\nindex 5be3d8a8f806d..d07ce478582d4 100644\n--- a/include/linux/mm.h\n+++ b/include/linux/mm.h\n@@ -1644,6 +1644,7 @@ void __folio_put(struct folio *folio);\n void split_page(struct page *page, unsigned int order);\n void folio_copy(struct folio *dst, struct folio *src);\n int folio_mc_copy(struct folio *dst, struct folio *src);\n+int folio_mc_copy_nt(struct folio *dst, struct folio *src);\n \n unsigned long nr_free_buffer_pages(void);\n \ndiff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h\nindex cd01dd7b3640d..e493207a3f46b 100644\n--- a/include/trace/events/migrate.h\n+++ b/include/trace/events/migrate.h\n@@ -9,6 +9,7 @@\n \n #define MIGRATE_MODE\t\t\t\t\t\t\\\n \tEM( MIGRATE_ASYNC,\t\"MIGRATE_ASYNC\")\t\t\\\n+\tEM(MIGRATE_ASYNC_NON_TEMPORAL_STORES,\t\t\"MIGRATE_ASYNC_NON_TEMPORAL_STORES\")\t\\\n \tEM( MIGRATE_SYNC_LIGHT,\t\"MIGRATE_SYNC_LIGHT\")\t\t\\\n \tEMe(MIGRATE_SYNC,\t\"MIGRATE_SYNC\")\n \ndiff --git a/mm/compaction.c b/mm/compaction.c\nindex 1e8f8eca318c6..cd26781b7376f 100644\n--- a/mm/compaction.c\n+++ b/mm/compaction.c\n@@ -444,7 +444,7 @@ static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)\n \t/* Update where async and sync compaction should restart */\n \tif (pfn \u003e zone-\u003ecompact_cached_migrate_pfn[0])\n \t\tzone-\u003ecompact_cached_migrate_pfn[0] = pfn;\n-\tif (cc-\u003emode != MIGRATE_ASYNC \u0026\u0026\n+\tif (!migrate_mode_is_async(cc-\u003emode) \u0026\u0026\n \t    pfn \u003e zone-\u003ecompact_cached_migrate_pfn[1])\n \t\tzone-\u003ecompact_cached_migrate_pfn[1] = pfn;\n }\n@@ -507,7 +507,7 @@ static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,\n \t__acquires(lock)\n {\n \t/* Track if the lock is contended in async mode */\n-\tif (cc-\u003emode == MIGRATE_ASYNC \u0026\u0026 !cc-\u003econtended) {\n+\tif (migrate_mode_is_async(cc-\u003emode) \u0026\u0026 !cc-\u003econtended) {\n \t\tif (spin_trylock_irqsave(lock, *flags))\n \t\t\treturn true;\n \n@@ -864,7 +864,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,\n \t\t\treturn -EAGAIN;\n \n \t\t/* async migration should just abort */\n-\t\tif (cc-\u003emode == MIGRATE_ASYNC)\n+\t\tif (migrate_mode_is_async(cc-\u003emode))\n \t\t\treturn -EAGAIN;\n \n \t\treclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);\n@@ -875,7 +875,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,\n \n \tcond_resched();\n \n-\tif (cc-\u003edirect_compaction \u0026\u0026 (cc-\u003emode == MIGRATE_ASYNC)) {\n+\tif (cc-\u003edirect_compaction \u0026\u0026 migrate_mode_is_async(cc-\u003emode)) {\n \t\tskip_on_failure = true;\n \t\tnext_skip_pfn = block_end_pfn(low_pfn, cc-\u003eorder);\n \t}\n@@ -1364,7 +1364,7 @@ static bool suitable_migration_source(struct compact_control *cc,\n \tif (pageblock_skip_persistent(page))\n \t\treturn false;\n \n-\tif ((cc-\u003emode != MIGRATE_ASYNC) || !cc-\u003edirect_compaction)\n+\tif (!migrate_mode_is_async(cc-\u003emode) || !cc-\u003edirect_compaction)\n \t\treturn true;\n \n \tblock_mt = get_pageblock_migratetype(page);\n@@ -1465,7 +1465,7 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)\n \t\treturn;\n \n \t/* Minimise scanning during async compaction */\n-\tif (cc-\u003edirect_compaction \u0026\u0026 cc-\u003emode == MIGRATE_ASYNC)\n+\tif (cc-\u003edirect_compaction \u0026\u0026 migrate_mode_is_async(cc-\u003emode))\n \t\treturn;\n \n \t/* Pageblock boundaries */\n@@ -1705,7 +1705,7 @@ static void isolate_freepages(struct compact_control *cc)\n \tblock_end_pfn = min(block_start_pfn + pageblock_nr_pages,\n \t\t\t\t\t\tzone_end_pfn(zone));\n \tlow_pfn = pageblock_end_pfn(cc-\u003emigrate_pfn);\n-\tstride = cc-\u003emode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;\n+\tstride = migrate_mode_is_async(cc-\u003emode) ? COMPACT_CLUSTER_MAX : 1;\n \n \t/*\n \t * Isolate free pages until enough are available to migrate the\n@@ -2514,7 +2514,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)\n \tunsigned long start_pfn = cc-\u003ezone-\u003ezone_start_pfn;\n \tunsigned long end_pfn = zone_end_pfn(cc-\u003ezone);\n \tunsigned long last_migrated_pfn;\n-\tconst bool sync = cc-\u003emode != MIGRATE_ASYNC;\n+\tconst bool sync = !migrate_mode_is_async(cc-\u003emode);\n \tbool update_cached;\n \tunsigned int nr_succeeded = 0, nr_migratepages;\n \tint order;\n@@ -2537,7 +2537,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)\n \t\tret = compaction_suit_allocation_order(cc-\u003ezone, cc-\u003eorder,\n \t\t\t\t\t\t       cc-\u003ehighest_zoneidx,\n \t\t\t\t\t\t       cc-\u003ealloc_flags,\n-\t\t\t\t\t\t       cc-\u003emode == MIGRATE_ASYNC,\n+\t\t\t\t\t\t       migrate_mode_is_async(cc-\u003emode),\n \t\t\t\t\t\t       !cc-\u003edirect_compaction);\n \t\tif (ret != COMPACT_CONTINUE)\n \t\t\treturn ret;\ndiff --git a/mm/migrate.c b/mm/migrate.c\nindex 2c3d489ecf51b..c7c62700d541c 100644\n--- a/mm/migrate.c\n+++ b/mm/migrate.c\n@@ -862,7 +862,10 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,\n \tif (folio_ref_count(src) != expected_count)\n \t\treturn -EAGAIN;\n \n-\trc = folio_mc_copy(dst, src);\n+\tif (mode == MIGRATE_ASYNC_NON_TEMPORAL_STORES)\n+\t\trc = folio_mc_copy_nt(dst, src);\n+\telse\n+\t\trc = folio_mc_copy(dst, src);\n \tif (unlikely(rc))\n \t\treturn rc;\n \n@@ -907,7 +910,7 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,\n \n \tdo {\n \t\tif (!trylock_buffer(bh)) {\n-\t\t\tif (mode == MIGRATE_ASYNC)\n+\t\t\tif (migrate_mode_is_async(mode))\n \t\t\t\tgoto unlock;\n \t\t\tif (mode == MIGRATE_SYNC_LIGHT \u0026\u0026 !buffer_uptodate(bh))\n \t\t\t\tgoto unlock;\n@@ -1220,7 +1223,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,\n \tdst-\u003eprivate = NULL;\n \n \tif (!folio_trylock(src)) {\n-\t\tif (mode == MIGRATE_ASYNC)\n+\t\tif (migrate_mode_is_async(mode))\n \t\t\tgoto out;\n \n \t\t/*\n@@ -1325,7 +1328,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,\n \t\t/* Establish migration ptes */\n \t\tVM_BUG_ON_FOLIO(folio_test_anon(src) \u0026\u0026\n \t\t\t       !folio_test_ksm(src) \u0026\u0026 !anon_vma, src);\n-\t\ttry_to_migrate(src, mode == MIGRATE_ASYNC ? TTU_BATCH_FLUSH : 0);\n+\t\ttry_to_migrate(src, migrate_mode_is_async(mode) ? TTU_BATCH_FLUSH : 0);\n \t\told_page_state |= PAGE_WAS_MAPPED;\n \t}\n \n@@ -1565,7 +1568,7 @@ static inline int try_split_folio(struct folio *folio, struct list_head *split_f\n {\n \tint rc;\n \n-\tif (mode == MIGRATE_ASYNC) {\n+\tif (migrate_mode_is_async(mode)) {\n \t\tif (!folio_trylock(folio))\n \t\t\treturn -EAGAIN;\n \t} else {\n@@ -1799,7 +1802,7 @@ static int migrate_pages_batch(struct list_head *from,\n \tLIST_HEAD(dst_folios);\n \tbool nosplit = (reason == MR_NUMA_MISPLACED);\n \n-\tVM_WARN_ON_ONCE(mode != MIGRATE_ASYNC \u0026\u0026\n+\tVM_WARN_ON_ONCE(!migrate_mode_is_async(mode) \u0026\u0026\n \t\t\t!list_empty(from) \u0026\u0026 !list_is_singular(from));\n \n \tfor (pass = 0; pass \u003c nr_pass \u0026\u0026 retry; pass++) {\n@@ -2081,6 +2084,11 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n \tLIST_HEAD(split_folios);\n \tstruct migrate_pages_stats stats;\n \n+\tif (IS_ENABLED(CONFIG_X86_64) \u0026\u0026\n+\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\n+\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\n+\t\tmode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n+\n \ttrace_mm_migrate_pages_start(mode, reason);\n \n \tmemset(\u0026stats, 0, sizeof(stats));\n@@ -2107,7 +2115,7 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n \t\tlist_cut_before(\u0026folios, from, \u0026folio2-\u003elru);\n \telse\n \t\tlist_splice_init(from, \u0026folios);\n-\tif (mode == MIGRATE_ASYNC)\n+\tif (migrate_mode_is_async(mode))\n \t\trc = migrate_pages_batch(\u0026folios, get_new_folio, put_new_folio,\n \t\t\t\tprivate, mode, reason, \u0026ret_folios,\n \t\t\t\t\u0026split_folios, \u0026stats,\ndiff --git a/mm/util.c b/mm/util.c\nindex b05ab6f97e110..e09e9b5f8eee9 100644\n--- a/mm/util.c\n+++ b/mm/util.c\n@@ -749,6 +749,23 @@ int folio_mc_copy(struct folio *dst, struct folio *src)\n }\n EXPORT_SYMBOL(folio_mc_copy);\n \n+int folio_mc_copy_nt(struct folio *dst, struct folio *src)\n+{\n+\tlong nr = folio_nr_pages(src);\n+\tlong i = 0;\n+\n+\tfor (;;) {\n+\t\tif (copy_mc_highpage_nt(folio_page(dst, i), folio_page(src, i)))\n+\t\t\treturn -EHWPOISON;\n+\t\tif (++i == nr)\n+\t\t\tbreak;\n+\t\tcond_resched();\n+\t}\n+\n+\treturn 0;\n+}\n+EXPORT_SYMBOL(folio_mc_copy_nt);\n+\n int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;\n static int sysctl_overcommit_ratio __read_mostly = 50;\n static unsigned long sysctl_overcommit_kbytes __read_mostly;\n"
}

best-expensive

null

{
  "EnableConfigs": [
    "NUMA",
    "MIGRATION"
  ],
  "FocusSymbols": [
    "copy_mc_to_kernel_nt",
    "folio_mc_copy_nt"
  ],
  "Reasoning": "The patch introduces a new memory migration mode `MIGRATE_ASYNC_NON_TEMPORAL_STORES` which uses non-temporal stores for memory demotion on x86_64. This is reachable via page reclaim (`shrink_folio_list` -\u003e `demote_folio_list` -\u003e `migrate_pages`) when memory demotion is enabled. The new functions `copy_mc_to_kernel_nt` and `folio_mc_copy_nt` perform the actual copying and should be focused during fuzzing.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
  even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).
- Code in vendor-specific PCIe switch, SmartNIC, or GPU drivers (e.g., mlxsw, pds_core, qed,
  ionic, amdgpu) that require physical PCIe hardware cards not emulated in standard QEMU.
- Driver .remove, .shutdown, or pci_unregister_driver teardown callbacks (e.g., igb_remove)
  that are executed only during PCI hot-unplug or sysfs driver unbind operations.

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
   Prefer non-static, non-inlined API entrypoint functions over internal static helper functions
   (which are inlined by the compiler and do not have distinct symbol addresses).
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Also check "depends on" lines in Kconfig to include any non-standard parent subsystem configs
   needed for Kbuild to compile the code statically into vmlinux. List them in the EnableConfigs
   output array, and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit b77301aee3a1dac3601dd685f20fa9adec71e06b
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Aug 1 04:39:47 2026 +0000

    syz-cluster: applied patch under review

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 367297b188c39..2d0938d3e372c 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -494,6 +494,10 @@ unsigned long __must_check
 copy_mc_to_kernel(void *to, const void *from, unsigned len);
 #define copy_mc_to_kernel copy_mc_to_kernel
 
+unsigned long __must_check
+copy_mc_to_kernel_nt(void *to, const void *from, unsigned len);
+#define copy_mc_to_kernel_nt copy_mc_to_kernel_nt
+
 unsigned long __must_check
 copy_mc_to_user(void __user *to, const void *from, unsigned len);
 #endif
diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c
index 97e88e58567bf..5a2ee5c2211ed 100644
--- a/arch/x86/lib/copy_mc.c
+++ b/arch/x86/lib/copy_mc.c
@@ -81,6 +81,32 @@ unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigne
 }
 EXPORT_SYMBOL_GPL(copy_mc_to_kernel);
 
+/**
+ * copy_mc_to_kernel_nt - memory copy that handles source exceptions
+ * if enabled, otherwise uses non-temporal stores
+ * @dst: destination address
+ * @src: source address
+ * @len: number of bytes to copy
+ *
+ * Return 0 for success, or number of bytes not copied if there was an
+ * exception.
+ */
+unsigned long __must_check copy_mc_to_kernel_nt(void *dst, const void *src, unsigned len)
+{
+	unsigned long ret;
+
+	if (copy_mc_fragile_enabled) {
+		instrument_memcpy_before(dst, src, len);
+		ret = copy_mc_fragile(dst, src, len);
+		instrument_memcpy_after(dst, src, len, ret);
+		return ret;
+	}
+
+	memcpy_flushcache(dst, src, len);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt);
+
 unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, unsigned len)
 {
 	unsigned long ret;
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 1ed4b3590b1ac..beae4441e0805 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -2119,7 +2119,7 @@ int nfs_migrate_folio(struct address_space *mapping, struct folio *dst,
 	}
 
 	if (folio_test_private_2(src)) { /* [DEPRECATED] */
-		if (mode == MIGRATE_ASYNC)
+		if (migrate_mode_is_async(mode))
 			return -EBUSY;
 		folio_wait_private_2(src);
 	}
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index af03db851a1d9..a5cb435b9ffe1 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -468,6 +468,32 @@ static inline int copy_mc_highpage(struct page *to, struct page *from)
 
 	return ret;
 }
+
+#ifdef copy_mc_to_kernel_nt
+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)
+{
+	unsigned long ret;
+	char *vfrom, *vto;
+
+	vfrom = kmap_local_page(from);
+	vto = kmap_local_page(to);
+	ret = copy_mc_to_kernel_nt(vto, vfrom, PAGE_SIZE);
+	if (!ret)
+		kmsan_copy_page_meta(to, from);
+	kunmap_local(vto);
+	kunmap_local(vfrom);
+
+	if (ret)
+		memory_failure_queue(page_to_pfn(from), 0);
+
+	return ret;
+}
+#else
+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)
+{
+	return copy_mc_highpage(to, from);
+}
+#endif
 #else
 static inline int copy_mc_user_highpage(struct page *to, struct page *from,
 					unsigned long vaddr, struct vm_area_struct *vma)
@@ -481,6 +507,12 @@ static inline int copy_mc_highpage(struct page *to, struct page *from)
 	copy_highpage(to, from);
 	return 0;
 }
+
+static inline int copy_mc_highpage_nt(struct page *to, struct page *from)
+{
+	copy_highpage(to, from);
+	return 0;
+}
 #endif
 
 static inline void memcpy_page(struct page *dst_page, size_t dst_off,
diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
index 265c4328b36ad..f7186e705b487 100644
--- a/include/linux/migrate_mode.h
+++ b/include/linux/migrate_mode.h
@@ -3,6 +3,8 @@
 #define MIGRATE_MODE_H_INCLUDED
 /*
  * MIGRATE_ASYNC means never block
+ * MIGRATE_ASYNC_NON_TEMPORAL_STORES means never block and use non-temporal
+ * stores if supported by the architecture
  * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
  *	on most operations but not ->writepage as the potential stall time
  *	is too significant
@@ -10,10 +12,17 @@
  */
 enum migrate_mode {
 	MIGRATE_ASYNC,
+	MIGRATE_ASYNC_NON_TEMPORAL_STORES,
 	MIGRATE_SYNC_LIGHT,
 	MIGRATE_SYNC,
 };
 
+static inline bool migrate_mode_is_async(enum migrate_mode mode)
+{
+	return mode == MIGRATE_ASYNC ||
+		mode == MIGRATE_ASYNC_NON_TEMPORAL_STORES;
+}
+
 enum migrate_reason {
 	MR_COMPACTION,
 	MR_MEMORY_FAILURE,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5be3d8a8f806d..d07ce478582d4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1644,6 +1644,7 @@ void __folio_put(struct folio *folio);
 void split_page(struct page *page, unsigned int order);
 void folio_copy(struct folio *dst, struct folio *src);
 int folio_mc_copy(struct folio *dst, struct folio *src);
+int folio_mc_copy_nt(struct folio *dst, struct folio *src);
 
 unsigned long nr_free_buffer_pages(void);
 
diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index cd01dd7b3640d..e493207a3f46b 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -9,6 +9,7 @@
 
 #define MIGRATE_MODE						\
 	EM( MIGRATE_ASYNC,	"MIGRATE_ASYNC")		\
+	EM(MIGRATE_ASYNC_NON_TEMPORAL_STORES,		"MIGRATE_ASYNC_NON_TEMPORAL_STORES")	\
 	EM( MIGRATE_SYNC_LIGHT,	"MIGRATE_SYNC_LIGHT")		\
 	EMe(MIGRATE_SYNC,	"MIGRATE_SYNC")
 
diff --git a/mm/compaction.c b/mm/compaction.c
index 1e8f8eca318c6..cd26781b7376f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -444,7 +444,7 @@ static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 	/* Update where async and sync compaction should restart */
 	if (pfn > zone->compact_cached_migrate_pfn[0])
 		zone->compact_cached_migrate_pfn[0] = pfn;
-	if (cc->mode != MIGRATE_ASYNC &&
+	if (!migrate_mode_is_async(cc->mode) &&
 	    pfn > zone->compact_cached_migrate_pfn[1])
 		zone->compact_cached_migrate_pfn[1] = pfn;
 }
@@ -507,7 +507,7 @@ static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
 	__acquires(lock)
 {
 	/* Track if the lock is contended in async mode */
-	if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
+	if (migrate_mode_is_async(cc->mode) && !cc->contended) {
 		if (spin_trylock_irqsave(lock, *flags))
 			return true;
 
@@ -864,7 +864,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			return -EAGAIN;
 
 		/* async migration should just abort */
-		if (cc->mode == MIGRATE_ASYNC)
+		if (migrate_mode_is_async(cc->mode))
 			return -EAGAIN;
 
 		reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
@@ -875,7 +875,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 	cond_resched();
 
-	if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
+	if (cc->direct_compaction && migrate_mode_is_async(cc->mode)) {
 		skip_on_failure = true;
 		next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 	}
@@ -1364,7 +1364,7 @@ static bool suitable_migration_source(struct compact_control *cc,
 	if (pageblock_skip_persistent(page))
 		return false;
 
-	if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
+	if (!migrate_mode_is_async(cc->mode) || !cc->direct_compaction)
 		return true;
 
 	block_mt = get_pageblock_migratetype(page);
@@ -1465,7 +1465,7 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)
 		return;
 
 	/* Minimise scanning during async compaction */
-	if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
+	if (cc->direct_compaction && migrate_mode_is_async(cc->mode))
 		return;
 
 	/* Pageblock boundaries */
@@ -1705,7 +1705,7 @@ static void isolate_freepages(struct compact_control *cc)
 	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
 						zone_end_pfn(zone));
 	low_pfn = pageblock_end_pfn(cc->migrate_pfn);
-	stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
+	stride = migrate_mode_is_async(cc->mode) ? COMPACT_CLUSTER_MAX : 1;
 
 	/*
 	 * Isolate free pages until enough are available to migrate the
@@ -2514,7 +2514,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 	unsigned long start_pfn = cc->zone->zone_start_pfn;
 	unsigned long end_pfn = zone_end_pfn(cc->zone);
 	unsigned long last_migrated_pfn;
-	const bool sync = cc->mode != MIGRATE_ASYNC;
+	const bool sync = !migrate_mode_is_async(cc->mode);
 	bool update_cached;
 	unsigned int nr_succeeded = 0, nr_migratepages;
 	int order;
@@ -2537,7 +2537,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 		ret = compaction_suit_allocation_order(cc->zone, cc->order,
 						       cc->highest_zoneidx,
 						       cc->alloc_flags,
-						       cc->mode == MIGRATE_ASYNC,
+						       migrate_mode_is_async(cc->mode),
 						       !cc->direct_compaction);
 		if (ret != COMPACT_CONTINUE)
 			return ret;
diff --git a/mm/migrate.c b/mm/migrate.c
index 2c3d489ecf51b..c7c62700d541c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -862,7 +862,10 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 
-	rc = folio_mc_copy(dst, src);
+	if (mode == MIGRATE_ASYNC_NON_TEMPORAL_STORES)
+		rc = folio_mc_copy_nt(dst, src);
+	else
+		rc = folio_mc_copy(dst, src);
 	if (unlikely(rc))
 		return rc;
 
@@ -907,7 +910,7 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head,
 
 	do {
 		if (!trylock_buffer(bh)) {
-			if (mode == MIGRATE_ASYNC)
+			if (migrate_mode_is_async(mode))
 				goto unlock;
 			if (mode == MIGRATE_SYNC_LIGHT && !buffer_uptodate(bh))
 				goto unlock;
@@ -1220,7 +1223,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 	dst->private = NULL;
 
 	if (!folio_trylock(src)) {
-		if (mode == MIGRATE_ASYNC)
+		if (migrate_mode_is_async(mode))
 			goto out;
 
 		/*
@@ -1325,7 +1328,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 		/* Establish migration ptes */
 		VM_BUG_ON_FOLIO(folio_test_anon(src) &&
 			       !folio_test_ksm(src) && !anon_vma, src);
-		try_to_migrate(src, mode == MIGRATE_ASYNC ? TTU_BATCH_FLUSH : 0);
+		try_to_migrate(src, migrate_mode_is_async(mode) ? TTU_BATCH_FLUSH : 0);
 		old_page_state |= PAGE_WAS_MAPPED;
 	}
 
@@ -1565,7 +1568,7 @@ static inline int try_split_folio(struct folio *folio, struct list_head *split_f
 {
 	int rc;
 
-	if (mode == MIGRATE_ASYNC) {
+	if (migrate_mode_is_async(mode)) {
 		if (!folio_trylock(folio))
 			return -EAGAIN;
 	} else {
@@ -1799,7 +1802,7 @@ static int migrate_pages_batch(struct list_head *from,
 	LIST_HEAD(dst_folios);
 	bool nosplit = (reason == MR_NUMA_MISPLACED);
 
-	VM_WARN_ON_ONCE(mode != MIGRATE_ASYNC &&
+	VM_WARN_ON_ONCE(!migrate_mode_is_async(mode) &&
 			!list_empty(from) && !list_is_singular(from));
 
 	for (pass = 0; pass < nr_pass && retry; pass++) {
@@ -2081,6 +2084,11 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
 	LIST_HEAD(split_folios);
 	struct migrate_pages_stats stats;
 
+	if (IS_ENABLED(CONFIG_X86_64) &&
+		IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) &&
+		reason == MR_DEMOTION && mode == MIGRATE_ASYNC)
+		mode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;
+
 	trace_mm_migrate_pages_start(mode, reason);
 
 	memset(&stats, 0, sizeof(stats));
@@ -2107,7 +2115,7 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
 		list_cut_before(&folios, from, &folio2->lru);
 	else
 		list_splice_init(from, &folios);
-	if (mode == MIGRATE_ASYNC)
+	if (migrate_mode_is_async(mode))
 		rc = migrate_pages_batch(&folios, get_new_folio, put_new_folio,
 				private, mode, reason, &ret_folios,
 				&split_folios, &stats,
diff --git a/mm/util.c b/mm/util.c
index b05ab6f97e110..e09e9b5f8eee9 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -749,6 +749,23 @@ int folio_mc_copy(struct folio *dst, struct folio *src)
 }
 EXPORT_SYMBOL(folio_mc_copy);
 
+int folio_mc_copy_nt(struct folio *dst, struct folio *src)
+{
+	long nr = folio_nr_pages(src);
+	long i = 0;
+
+	for (;;) {
+		if (copy_mc_highpage_nt(folio_page(dst, i), folio_page(src, i)))
+			return -EHWPOISON;
+		if (++i == nr)
+			break;
+		cond_resched();
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(folio_mc_copy_nt);
+
 int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
 static int sysctl_overcommit_ratio __read_mostly = 50;
 static unsigned long sysctl_overcommit_kbytes __read_mostly;

gemini-3.1-pro-preview

null

null

							input: 6946
							output: 19
							thoughts: 245
						

**My Initial Assessment of the Non-Temporal Store Patch**

Okay, so I'm looking at this patch and it's introducing a few new functions: `copy_mc_to_kernel_nt`, `copy_mc_highpage_nt`, and `folio_mc_copy_nt`, along with a new migration mode, `MIGRATE_ASYNC_NON_TEMPORAL_STORES`. My initial thought is this is targeting some specific optimization around memory migration, probably leveraging non-temporal stores for performance. And the code is going to use `MIGRATE_ASYNC_NON_TEMPORAL_STORES` with `migrate_pages` under certain conditions. Specifically, when `IS_ENABLED(CONFIG_X86_64)` and `IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE)` are true, and the reason for migration is `MR_DEMOTION` and the migration `mode` is `MIGRATE_ASYNC`.

So, it's pretty clear this is a functional change to the memory migration subsystem, specifically focused on demotion on x86_64 architectures. The key is to understand when this path actually gets hit. I need to make sure the assumptions are correct regarding the configurations. Specifically, are the configurations `CONFIG_X86_64` and `CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE` always set in the target environments? Also, I need to understand the implications of `MR_DEMOTION`. That likely relates to NUMA balancing or memory tiering, and I need to investigate where this reason is used and how it ties into the overall memory management strategy. Time to search for occurrences of `MR_DEMOTION` and dig into those call sites.

{
  "Expression": "MR_DEMOTION"
}

{
  "Output": "include/linux/migrate_mode.h=26=enum migrate_reason {\n--\ninclude/linux/migrate_mode.h-34-\tMR_LONGTERM_PIN,\ninclude/linux/migrate_mode.h:35:\tMR_DEMOTION,\ninclude/linux/migrate_mode.h-36-\tMR_DAMON,\n--\ninclude/trace/events/migrate.h-25-\tEM( MR_LONGTERM_PIN,\t\"longterm_pin\")\t\t\t\\\ninclude/trace/events/migrate.h:26:\tEM( MR_DEMOTION,\t\"demotion\")\t\t\t\\\ninclude/trace/events/migrate.h-27-\tEMe(MR_DAMON,\t\t\"damon\")\n--\nmm/migrate.c=1193=static void migrate_folio_done(struct folio *src,\n--\nmm/migrate.c-1195-{\nmm/migrate.c:1196:\tif (likely(!page_has_movable_ops(\u0026src-\u003epage)) \u0026\u0026 reason != MR_DEMOTION)\nmm/migrate.c-1197-\t\tmod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +\n--\nmm/migrate.c=2075=int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n--\nmm/migrate.c-2088-\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\nmm/migrate.c:2089:\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\nmm/migrate.c-2090-\t\tmode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n--\nmm/vmscan.c=1021=static unsigned int demote_folio_list(struct list_head *demote_folios,\n--\nmm/vmscan.c-1037-\t\t.nmask = \u0026allowed_mask,\nmm/vmscan.c:1038:\t\t.reason = MR_DEMOTION,\nmm/vmscan.c-1039-\t};\n--\nmm/vmscan.c-1057-\tmigrate_pages(demote_folios, alloc_demote_folio, NULL,\nmm/vmscan.c:1058:\t\t      (unsigned long)\u0026mtc, MIGRATE_ASYNC, MR_DEMOTION,\nmm/vmscan.c-1059-\t\t      \u0026nr_succeeded);\n"
}

gemini-3.1-pro-preview

null

null

							input: 8209
							output: 20
							thoughts: 35
						

Okay, here's my take on those thoughts, framed from my perspective as a code expert:

**Investigating the `demote_folio_list` Function**

Right, so I'm thinking about memory management, and this `demote_folio_list` function has popped up. The comment pointed me to it, and I've traced its location in `mm/vmscan.c`. Alright, let's take a closer look at `demote_folio_list`. This probably deals with moving folios to a lower priority state, likely for memory reclaim or perhaps aging them out. I need to understand exactly what criteria are being used, what states are involved, and what the implications are for performance and overall system stability. I'm going to start by analyzing the code itself, paying close attention to any locks or synchronization mechanisms used within the function and how they are handled. I'll also check any calls to it and from where the folios it operates upon originates.

{
  "Expression": "demote_folio_list"
}

{
  "Output": "mm/vmscan.c=986=static struct folio *alloc_demote_folio(struct folio *src,\n--\nmm/vmscan.c-1020- */\nmm/vmscan.c:1021:static unsigned int demote_folio_list(struct list_head *demote_folios,\nmm/vmscan.c-1022-\t\t\t\t      struct pglist_data *pgdat,\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1575-\t/* Migrate folios selected for demotion */\nmm/vmscan.c:1576:\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\nmm/vmscan.c-1577-\tnr_reclaimed += nr_demoted;\n"
}

gemini-3.1-pro-preview

null

null

							input: 8702
							output: 32
							thoughts: 78
						

Here's my take on the process, thinking through the memory demotion logic:

**Diving into Folio Demotion**

Okay, so `shrink_folio_list` is the function that actually kicks off the page reclaim process. It's calling `demote_folio_list`, which immediately tells me this is the heart of the page reclaim strategy. It's the critical bit for actually getting memory back.

Now, when can we actually *do* this demotion? It's clearly tied to NUMA, Migration and probably Memory Tiering, I'd bet. I should confirm that, just to be thorough.

Let's dive into `mm/vmscan.c` and take a look at the implementation for `demote_folio_list`. That's where the rubber meets the road. I'll check its conditions and how it's actually moving things around. This is where I can really understand what's *actually* happening under the hood.

{
  "Expression": "demote_folio_list",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=986=static struct folio *alloc_demote_folio(struct folio *src,\n--\nmm/vmscan.c-1020- */\nmm/vmscan.c:1021:static unsigned int demote_folio_list(struct list_head *demote_folios,\nmm/vmscan.c-1022-\t\t\t\t      struct pglist_data *pgdat,\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1575-\t/* Migrate folios selected for demotion */\nmm/vmscan.c:1576:\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\nmm/vmscan.c-1577-\tnr_reclaimed += nr_demoted;\n"
}

gemini-3.1-pro-preview

null

null

							input: 9252
							output: 35
							thoughts: 21
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Diving into `mm/vmscan.c`**

Okay, let's zero in on `mm/vmscan.c`, specifically around line 1021. I'm probably after something related to memory reclaim or scanning behavior – that's the usual territory there. I'm trying to get a clearer understanding of how the virtual memory subsystem is behaving, and my experience tells me that area is a likely candidate to find relevant details about the implementation. I need to understand this implementation to fix the issue I'm dealing with. I know what problem I am attempting to solve and that information I can obtain from the code around this area will provide some useful insight.

{
  "File": "mm/vmscan.c",
  "FirstLine": 1010,
  "LineCount": 50
}

{
  "Contents": "1010:\t\n1011:\t\tmtc-\u003egfp_mask \u0026= ~__GFP_THISNODE;\n1012:\t\tmtc-\u003enmask = allowed_mask;\n1013:\t\n1014:\t\treturn alloc_migration_target(src, (unsigned long)mtc);\n1015:\t}\n1016:\t\n1017:\t/*\n1018:\t * Take folios on @demote_folios and attempt to demote them to another node.\n1019:\t * Folios which are not demoted are left on @demote_folios.\n1020:\t */\n1021:\tstatic unsigned int demote_folio_list(struct list_head *demote_folios,\n1022:\t\t\t\t\t      struct pglist_data *pgdat,\n1023:\t\t\t\t\t      struct mem_cgroup *memcg)\n1024:\t{\n1025:\t\tint target_nid;\n1026:\t\tunsigned int nr_succeeded;\n1027:\t\tnodemask_t allowed_mask;\n1028:\t\n1029:\t\tstruct migration_target_control mtc = {\n1030:\t\t\t/*\n1031:\t\t\t * Allocate from 'node', or fail quickly and quietly.\n1032:\t\t\t * When this happens, 'page' will likely just be discarded\n1033:\t\t\t * instead of migrated.\n1034:\t\t\t */\n1035:\t\t\t.gfp_mask = (GFP_HIGHUSER_MOVABLE \u0026 ~__GFP_RECLAIM) |\n1036:\t\t\t\t__GFP_NOMEMALLOC | GFP_NOWAIT,\n1037:\t\t\t.nmask = \u0026allowed_mask,\n1038:\t\t\t.reason = MR_DEMOTION,\n1039:\t\t};\n1040:\t\n1041:\t\tif (list_empty(demote_folios))\n1042:\t\t\treturn 0;\n1043:\t\n1044:\t\tnode_get_allowed_targets(pgdat, \u0026allowed_mask);\n1045:\t\tmem_cgroup_node_filter_allowed(memcg, \u0026allowed_mask);\n1046:\t\tif (nodes_empty(allowed_mask))\n1047:\t\t\treturn 0;\n1048:\t\n1049:\t\ttarget_nid = next_demotion_node(pgdat-\u003enode_id, \u0026allowed_mask);\n1050:\t\tif (target_nid == NUMA_NO_NODE)\n1051:\t\t\t/* No lower-tier nodes or nodes were hot-unplugged. */\n1052:\t\t\treturn 0;\n1053:\t\n1054:\t\tmtc.nid = target_nid;\n1055:\t\n1056:\t\t/* Demotion ignores all cpuset and mempolicy settings */\n1057:\t\tmigrate_pages(demote_folios, alloc_demote_folio, NULL,\n1058:\t\t\t      (unsigned long)\u0026mtc, MIGRATE_ASYNC, MR_DEMOTION,\n1059:\t\t\t      \u0026nr_succeeded);\n"
}

gemini-3.1-pro-preview

null

null

							input: 10257
							output: 24
							thoughts: 93
						

**Analyzing the `demote_folio_list` Function's Behavior**

Okay, so I'm tracing the execution path here. It looks like `demote_folio_list` is calling `migrate_pages` with `MIGRATE_ASYNC` and `MR_DEMOTION` flags. That's the key. This should be triggering the new code path within `migrate_pages`, which is what I'm interested in understanding. Now, that new code path seems to be conditional. It's only going to execute if both `CONFIG_X86_64` and `CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE` are defined. `CONFIG_X86_64` is probably a given these days, but it's important to remember it. The more interesting part, then, is this `CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE` condition. I should probably double-check the definition of `CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE`. This seems like the critical piece that I need to investigate further.

{
  "Expression": "ARCH_HAS_UACCESS_FLUSHCACHE"
}

{
  "Output": "arch/arm64/Kconfig=1886=config ARM64_PMEM\n--\narch/arm64/Kconfig-1888-\tselect ARCH_HAS_PMEM_API\narch/arm64/Kconfig:1889:\tselect ARCH_HAS_UACCESS_FLUSHCACHE\narch/arm64/Kconfig-1890-\thelp\n--\narch/arm64/include/asm/string.h=44=extern void *__memset(void *, int, __kernel_size_t);\narch/arm64/include/asm/string.h-45-\narch/arm64/include/asm/string.h:46:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\narch/arm64/include/asm/string.h-47-#define __HAVE_ARCH_MEMCPY_FLUSHCACHE\n--\narch/arm64/include/asm/uaccess.h=476=extern __must_check long strnlen_user(const char __user *str, long n);\narch/arm64/include/asm/uaccess.h-477-\narch/arm64/include/asm/uaccess.h:478:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\narch/arm64/include/asm/uaccess.h-479-extern unsigned long __must_check __copy_user_flushcache(void *to, const void __user *from, unsigned long n);\n--\narch/arm64/lib/Makefile=12=endif\narch/arm64/lib/Makefile-13-\narch/arm64/lib/Makefile:14:lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o\narch/arm64/lib/Makefile-15-\n--\narch/powerpc/Kconfig=118=config PPC\n--\narch/powerpc/Kconfig-159-\tselect ARCH_HAS_TICK_BROADCAST\t\tif GENERIC_CLOCKEVENTS_BROADCAST\narch/powerpc/Kconfig:160:\tselect ARCH_HAS_UACCESS_FLUSHCACHE\narch/powerpc/Kconfig-161-\tselect ARCH_HAS_UBSAN\n--\narch/powerpc/lib/pmem.c=64=EXPORT_SYMBOL_GPL(arch_invalidate_pmem);\n--\narch/powerpc/lib/pmem.c-66-/*\narch/powerpc/lib/pmem.c:67: * CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE symbols\narch/powerpc/lib/pmem.c-68- */\n--\narch/x86/Kconfig=58=config X86\n--\narch/x86/Kconfig-103-\tselect ARCH_HAS_NONLEAF_PMD_YOUNG\tif PGTABLE_LEVELS \u003e 2\narch/x86/Kconfig:104:\tselect ARCH_HAS_UACCESS_FLUSHCACHE\tif X86_64\narch/x86/Kconfig-105-\tselect ARCH_HAS_COPY_MC\t\t\tif X86_64\n--\narch/x86/include/asm/string_64.h=80=int strcmp(const char *cs, const char *ct);\narch/x86/include/asm/string_64.h-81-\narch/x86/include/asm/string_64.h:82:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\narch/x86/include/asm/string_64.h-83-#define __HAVE_ARCH_MEMCPY_FLUSHCACHE 1\n--\narch/x86/lib/usercopy_64.c-17-\narch/x86/lib/usercopy_64.c:18:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\narch/x86/lib/usercopy_64.c-19-/**\n--\ndrivers/nvdimm/pmem.c=448=static int pmem_attach_disk(struct device *dev,\n--\ndrivers/nvdimm/pmem.c-493-\tfua = nvdimm_has_flush(nd_region);\ndrivers/nvdimm/pmem.c:494:\tif (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) || fua \u003c 0) {\ndrivers/nvdimm/pmem.c-495-\t\tdev_warn(dev, \"unable to guarantee persistence of writes\\n\");\n--\ninclude/linux/uio.h=261=bool copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i)\n--\ninclude/linux/uio.h-269-\ninclude/linux/uio.h:270:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\ninclude/linux/uio.h-271-/*\n--\ninclude/linux/uio.h-273- * _copy_from_iter_flushcache() than _copy_from_iter_nocache() must check for\ninclude/linux/uio.h:274: * IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) before assuming that the\ninclude/linux/uio.h-275- * destination is flushed from the cache on return.\n--\nlib/Kconfig=539=config UACCESS_MEMCPY\n--\nlib/Kconfig-541-\nlib/Kconfig:542:config ARCH_HAS_UACCESS_FLUSHCACHE\nlib/Kconfig-543-\tbool\n--\nlib/iov_iter.c=292=EXPORT_SYMBOL(_copy_from_iter_nocache);\nlib/iov_iter.c-293-\nlib/iov_iter.c:294:#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE\nlib/iov_iter.c-295-static __always_inline\n--\nmm/migrate.c=2075=int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n--\nmm/migrate.c-2087-\tif (IS_ENABLED(CONFIG_X86_64) \u0026\u0026\nmm/migrate.c:2088:\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\nmm/migrate.c-2089-\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\n"
}

gemini-3.1-pro-preview

null

null

							input: 12215
							output: 27
							thoughts: 105
						

**My Analysis of Memory Tiering and X86_64 Interaction**

Okay, so I'm looking at how memory tiering interacts with the x86_64 architecture. I see that `ARCH_HAS_UACCESS_FLUSHCACHE` is automatically selected when `X86_64` is enabled. That simplifies things a bit; on x86_64, `ARCH_HAS_UACCESS_FLUSHCACHE` is essentially always on. Now, to get `MR_DEMOTION` triggered – which is what I'm really trying to understand here – I know I need both NUMA support and some form of memory tiering. It looks like the relevant configuration options that will lead to this behavior are `CONFIG_MEMORY_TIERING`, or perhaps `CONFIG_NUMA_BALANCING`, or even `CONFIG_MIGRATION`. I need to dig into those configurations now to understand the precise conditions for the demotion logic. I'll need to see how these interact, especially considering that the underlying architecture has the uaccess cache flush built in.

{
  "Expression": "MR_DEMOTION",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/migrate.c=1193=static void migrate_folio_done(struct folio *src,\n--\nmm/migrate.c-1195-{\nmm/migrate.c:1196:\tif (likely(!page_has_movable_ops(\u0026src-\u003epage)) \u0026\u0026 reason != MR_DEMOTION)\nmm/migrate.c-1197-\t\tmod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +\n--\nmm/migrate.c=2075=int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n--\nmm/migrate.c-2088-\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\nmm/migrate.c:2089:\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\nmm/migrate.c-2090-\t\tmode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n--\nmm/vmscan.c=1021=static unsigned int demote_folio_list(struct list_head *demote_folios,\n--\nmm/vmscan.c-1037-\t\t.nmask = \u0026allowed_mask,\nmm/vmscan.c:1038:\t\t.reason = MR_DEMOTION,\nmm/vmscan.c-1039-\t};\n--\nmm/vmscan.c-1057-\tmigrate_pages(demote_folios, alloc_demote_folio, NULL,\nmm/vmscan.c:1058:\t\t      (unsigned long)\u0026mtc, MIGRATE_ASYNC, MR_DEMOTION,\nmm/vmscan.c-1059-\t\t      \u0026nr_succeeded);\n"
}

gemini-3.1-pro-preview

null

null

							input: 13020
							output: 32
							thoughts: 24
						

Here's my thought process, as it relates to checking `mm/vmscan.c` for `demote_folio_list` ifdefs:

**Diving into `mm/vmscan.c` and `demote_folio_list`**

Okay, so I need to understand how `demote_folio_list` is being used, especially if there are any conditional compilations related to it. That tells me what scenarios its functionality is tied to. The obvious first step is to dive into `mm/vmscan.c` and search for any `#ifdef` or `#if` preprocessor directives surrounding the use of `demote_folio_list`. This will help me quickly identify the different configurations where this function's logic is active or disabled.

{
  "Expression": "demote_folio_list",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=986=static struct folio *alloc_demote_folio(struct folio *src,\n--\nmm/vmscan.c-1020- */\nmm/vmscan.c:1021:static unsigned int demote_folio_list(struct list_head *demote_folios,\nmm/vmscan.c-1022-\t\t\t\t      struct pglist_data *pgdat,\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1575-\t/* Migrate folios selected for demotion */\nmm/vmscan.c:1576:\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\nmm/vmscan.c-1577-\tnr_reclaimed += nr_demoted;\n"
}

gemini-3.1-pro-preview

null

null

							input: 13470
							output: 34
							thoughts: 19
						

Okay, let's see if I understand this.

**Investigating Conditional Compilation of `demote_folio_list`**

Right, so I need to figure out the scope of `demote_folio_list`. The key here is whether it's wrapped inside any `#ifdef` preprocessor directives. I need to determine if the presence or absence of this function is controlled by some conditional compilation flag. Knowing if it's "ifdef-ed" will fundamentally change how I interpret its usage and how it fits into the overall build process. This is the first question I need to answer to fully grasp its role.

{
  "File": "mm/vmscan.c",
  "FirstLine": 980,
  "LineCount": 50
}

{
  "Contents": " 980:\t\n 981:\t\tmapping = folio_mapping(folio);\n 982:\t\tif (mapping \u0026\u0026 mapping-\u003ea_ops-\u003eis_dirty_writeback)\n 983:\t\t\tmapping-\u003ea_ops-\u003eis_dirty_writeback(folio, dirty, writeback);\n 984:\t}\n 985:\t\n 986:\tstatic struct folio *alloc_demote_folio(struct folio *src,\n 987:\t\t\tunsigned long private)\n 988:\t{\n 989:\t\tstruct folio *dst;\n 990:\t\tnodemask_t *allowed_mask;\n 991:\t\tstruct migration_target_control *mtc;\n 992:\t\n 993:\t\tmtc = (struct migration_target_control *)private;\n 994:\t\n 995:\t\tallowed_mask = mtc-\u003enmask;\n 996:\t\t/*\n 997:\t\t * make sure we allocate from the target node first also trying to\n 998:\t\t * demote or reclaim pages from the target node via kswapd if we are\n 999:\t\t * low on free memory on target node. If we don't do this and if\n1000:\t\t * we have free memory on the slower(lower) memtier, we would start\n1001:\t\t * allocating pages from slower(lower) memory tiers without even forcing\n1002:\t\t * a demotion of cold pages from the target memtier. This can result\n1003:\t\t * in the kernel placing hot pages in slower(lower) memory tiers.\n1004:\t\t */\n1005:\t\tmtc-\u003enmask = NULL;\n1006:\t\tmtc-\u003egfp_mask |= __GFP_THISNODE;\n1007:\t\tdst = alloc_migration_target(src, (unsigned long)mtc);\n1008:\t\tif (dst)\n1009:\t\t\treturn dst;\n1010:\t\n1011:\t\tmtc-\u003egfp_mask \u0026= ~__GFP_THISNODE;\n1012:\t\tmtc-\u003enmask = allowed_mask;\n1013:\t\n1014:\t\treturn alloc_migration_target(src, (unsigned long)mtc);\n1015:\t}\n1016:\t\n1017:\t/*\n1018:\t * Take folios on @demote_folios and attempt to demote them to another node.\n1019:\t * Folios which are not demoted are left on @demote_folios.\n1020:\t */\n1021:\tstatic unsigned int demote_folio_list(struct list_head *demote_folios,\n1022:\t\t\t\t\t      struct pglist_data *pgdat,\n1023:\t\t\t\t\t      struct mem_cgroup *memcg)\n1024:\t{\n1025:\t\tint target_nid;\n1026:\t\tunsigned int nr_succeeded;\n1027:\t\tnodemask_t allowed_mask;\n1028:\t\n1029:\t\tstruct migration_target_control mtc = {\n"
}

gemini-3.1-pro-preview

null

null

							input: 14440
							output: 20
							thoughts: 41
						

Okay, here's my understanding, expressed as your inner monologue:

**Investigating a Potentially Unexpected Call**

Alright, I'm looking at this code and I see no preprocessor directives, specifically no `#ifdef` statements, guarding `demote_folio_list`. That's a bit odd. I was expecting some kind of conditional compilation there. But hold on... I see that `next_demotion_node` is being called. So, despite the apparent lack of a condition, something *is* using the `demote_folio_list` function. I need to understand why this function is being called, even without a preprocessor directive controlling it. I'll need to dig into the definition and usage of `next_demotion_node` to see how it relates to `demote_folio_list`. Clearly, there is an execution path to it. This warrants further investigation. Let me look at the implementation of `next_demotion_node`.

{
  "Expression": "next_demotion_node"
}

{
  "Output": "include/linux/memory-tiers.h=54=void mt_put_memory_types(struct list_head *memory_types);\ninclude/linux/memory-tiers.h-55-#ifdef CONFIG_MIGRATION\ninclude/linux/memory-tiers.h:56:int next_demotion_node(int node, const nodemask_t *allowed_mask);\ninclude/linux/memory-tiers.h-57-void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);\ninclude/linux/memory-tiers.h=58=bool node_is_toptier(int node);\ninclude/linux/memory-tiers.h-59-#else\ninclude/linux/memory-tiers.h:60:static inline int next_demotion_node(int node, const nodemask_t *allowed_mask)\ninclude/linux/memory-tiers.h-61-{\n--\ninclude/linux/memory-tiers.h=99=static inline void clear_node_memory_type(int node, struct memory_dev_type *memtype)\n--\ninclude/linux/memory-tiers.h-103-\ninclude/linux/memory-tiers.h:104:static inline int next_demotion_node(int node, const nodemask_t *allowed_mask)\ninclude/linux/memory-tiers.h-105-{\n--\nmm/memory-tiers.c=302=void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)\n--\nmm/memory-tiers.c-320-/**\nmm/memory-tiers.c:321: * next_demotion_node() - Get the next node in the demotion path\nmm/memory-tiers.c-322- * @node: The starting node to lookup the next node\n--\nmm/memory-tiers.c-329- */\nmm/memory-tiers.c:330:int next_demotion_node(int node, const nodemask_t *allowed_mask)\nmm/memory-tiers.c-331-{\n--\nmm/vmscan.c=1021=static unsigned int demote_folio_list(struct list_head *demote_folios,\n--\nmm/vmscan.c-1048-\nmm/vmscan.c:1049:\ttarget_nid = next_demotion_node(pgdat-\u003enode_id, \u0026allowed_mask);\nmm/vmscan.c-1050-\tif (target_nid == NUMA_NO_NODE)\n"
}

gemini-3.1-pro-preview

null

null

							input: 15341
							output: 19
							thoughts: 62
						

**Analyzing the Memory Tier Demotion Node**

Okay, so I'm looking at `next_demotion_node`. I remember seeing that one; it's defined within `mm/memory-tiers.c`, but only if `CONFIG_MIGRATION` is enabled. And, of course, that implies `CONFIG_NUMA` is also in the mix for memory tiers. I need to make sure I understand the Kconfig dependencies involved here. Time to dive into `mm/memory-tiers.c` and figure out those Kconfig configurations. What else do I need to keep in mind here?

{
  "Expression": "memory-tiers.o"
}

{
  "Output": "mm/Makefile=98=obj-$(CONFIG_MIGRATION) += migrate.o\nmm/Makefile:99:obj-$(CONFIG_NUMA) += memory-tiers.o\nmm/Makefile-100-obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o\n"
}

gemini-3.1-pro-preview

null

null

							input: 15631
							output: 19
							thoughts: 171
						

**Analyzing the Build Dependencies**

Okay, so I'm looking at this code and it seems pretty straightforward. It's clear that to get `memory-tiers.o` to build, I'm going to need `CONFIG_NUMA` enabled. That makes perfect sense; NUMA is fundamental to tiered memory architectures. And, digging a little deeper, I see that `CONFIG_MIGRATION` is essential, specifically to make sure that `next_demotion_node` isn't just a placeholder or stub function. That points directly to the memory migration code, so `CONFIG_MIGRATION` is a must-have.

Let's quickly verify that, I'll go check `mm/migrate.c`. As expected, that file is definitely compiled only if `CONFIG_MIGRATION` is defined. This confirms the initial dependency.

Alright, so the patch itself is modifying several core memory management files: `mm/migrate.c`, `mm/compaction.c`, `mm/vmscan.c`, and `mm/util.c`. That's a pretty broad touch, implying this is a deeper change than just a simple fix; it's likely a significant improvement to the memory management subsystem. Plus, it's also touching `arch/x86/lib/copy_mc.c`, which makes sense because this is architecture-specific code for memory copy operations.

The new function `copy_mc_to_kernel_nt` is specifically defined in `arch/x86/lib/copy_mc.c`. Since it's a new function, it is good to investigate exactly what it does, because that's always an important detail to check. I should verify that the build system includes this file. I'll take a look at the `arch/x86/lib/Makefile` to confirm the compilation of `copy_mc.c`. This should give me a better understanding of how the new code integrates into the existing architecture-specific routines.

{
  "Expression": "copy_mc.o"
}

{
  "Output": "arch/x86/lib/Makefile=34=lib-y += pc-conf-reg.o\narch/x86/lib/Makefile:35:lib-$(CONFIG_ARCH_HAS_COPY_MC) += copy_mc.o copy_mc_64.o\narch/x86/lib/Makefile-36-lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o\n"
}

gemini-3.1-pro-preview

null

null

							input: 16363
							output: 21
							thoughts: 30
						

Okay, here's my interpretation of that thought process, as if I were thinking it myself, with a focus on delivering a "fulsome summary" for another expert:

**Investigating `CONFIG_ARCH_HAS_COPY_MC` Dependency**

Right, so I see a requirement pop up for `CONFIG_ARCH_HAS_COPY_MC`. My immediate thought is, "What's driving this? Why is this feature needed, and more importantly, what's *selecting* it?" I need to understand the dependencies and the context. This isn't just a random option; something, somewhere, is mandating its inclusion.

My next step is clearly to go digging into the Kconfig files. I need to trace back from this option to find the relevant `select` statements. I'm looking for the conditions – the architecture-specific features, the higher-level functionality – that trigger this option's enablement. I’m thinking, maybe it's something related to memory management, optimized data copying, or perhaps even specific hardware capabilities. I expect it'll be somewhere in the architecture-specific Kconfig fragments, but it’s always good to be thorough. I'll probably start with a grep to find it and follow the leads, because that's what makes the most sense. Understanding the 'why' is crucial for proper integration and avoiding potential conflicts down the line. I'll be looking for clues in the surrounding code as well – comments, other dependencies, anything that sheds light on the reasoning.

{
  "Expression": "ARCH_HAS_COPY_MC"
}

{
  "Output": "arch/powerpc/Kconfig=118=config PPC\n--\narch/powerpc/Kconfig-129-\tselect ARCH_ENABLE_MEMORY_HOTREMOVE\narch/powerpc/Kconfig:130:\tselect ARCH_HAS_COPY_MC\t\t\tif PPC64\narch/powerpc/Kconfig-131-\tselect ARCH_HAS_CURRENT_STACK_POINTER\n--\narch/powerpc/include/asm/uaccess.h=384=extern __must_check long strnlen_user(const char __user *str, long n);\narch/powerpc/include/asm/uaccess.h-385-\narch/powerpc/include/asm/uaccess.h:386:#ifdef CONFIG_ARCH_HAS_COPY_MC\narch/powerpc/include/asm/uaccess.h-387-unsigned long __must_check\n--\narch/x86/Kconfig=58=config X86\n--\narch/x86/Kconfig-104-\tselect ARCH_HAS_UACCESS_FLUSHCACHE\tif X86_64\narch/x86/Kconfig:105:\tselect ARCH_HAS_COPY_MC\t\t\tif X86_64\narch/x86/Kconfig-106-\tselect ARCH_HAS_SET_MEMORY\n--\narch/x86/include/asm/mce.h=237=extern int mce_p5_enabled;\narch/x86/include/asm/mce.h-238-\narch/x86/include/asm/mce.h:239:#ifdef CONFIG_ARCH_HAS_COPY_MC\narch/x86/include/asm/mce.h-240-extern void enable_copy_mc_fragile(void);\n--\narch/x86/include/asm/uaccess.h=490=extern __must_check long strnlen_user(const char __user *str, long n);\narch/x86/include/asm/uaccess.h-491-\narch/x86/include/asm/uaccess.h:492:#ifdef CONFIG_ARCH_HAS_COPY_MC\narch/x86/include/asm/uaccess.h-493-unsigned long __must_check\n--\narch/x86/lib/Makefile=34=lib-y += pc-conf-reg.o\narch/x86/lib/Makefile:35:lib-$(CONFIG_ARCH_HAS_COPY_MC) += copy_mc.o copy_mc_64.o\narch/x86/lib/Makefile-36-lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o\n--\ndrivers/md/dm-writecache.c=46=do {\t\t\t\t\t\t\t\t\\\n--\ndrivers/md/dm-writecache.c-53-\ndrivers/md/dm-writecache.c:54:#if IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC) \u0026\u0026 defined(DM_WRITECACHE_HAS_PMEM)\ndrivers/md/dm-writecache.c-55-#define DM_WRITECACHE_HANDLE_HARDWARE_ERRORS\n--\ninclude/linux/uio.h=277=size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i);\n--\ninclude/linux/uio.h-281-\ninclude/linux/uio.h:282:#ifdef CONFIG_ARCH_HAS_COPY_MC\ninclude/linux/uio.h-283-size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i);\n--\nlib/Kconfig=542=config ARCH_HAS_UACCESS_FLUSHCACHE\n--\nlib/Kconfig-549-# buffer.\nlib/Kconfig:550:config ARCH_HAS_COPY_MC\nlib/Kconfig-551-\tbool\n--\nlib/iov_iter.c=200=EXPORT_SYMBOL(_copy_to_iter);\nlib/iov_iter.c-201-\nlib/iov_iter.c:202:#ifdef CONFIG_ARCH_HAS_COPY_MC\nlib/iov_iter.c-203-static __always_inline\n--\nlib/iov_iter.c=255=EXPORT_SYMBOL_GPL(_copy_mc_to_iter);\nlib/iov_iter.c:256:#endif /* CONFIG_ARCH_HAS_COPY_MC */\nlib/iov_iter.c-257-\n"
}

gemini-3.1-pro-preview

null

null

							input: 17853
							output: 19
							thoughts: 410
						

**Analyzing Memory Demotion and `migrate_pages` on x86_64**

Okay, so I'm looking at this patch and how it interacts with memory migration, specifically on x86_64. The first thing that jumps out is that the code leverages `ARCH_HAS_COPY_MC`, which, on x86_64, also means we're dealing with `ARCH_HAS_UACCESS_FLUSHCACHE`. Good, that makes sense. We're talking about non-temporal stores, so caching is important.

The patch modifies `copy_mc_to_kernel_nt` and `folio_mc_copy_nt`, hinting at optimized memory copies. That's the baseline. The real interesting part is the `migrate_pages` modification. It's using `MIGRATE_ASYNC_NON_TEMPORAL_STORES` when the `reason` is `MR_DEMOTION` and the `mode` is `MIGRATE_ASYNC`. This happens during the demotion process, specifically when `demote_folio_list` gets called. Right, page reclaim. This whole thing hinges on memory demotion.

To make this happen, we need NUMA, migration enabled, and multiple memory nodes, which I assume is standard for a NUMA configuration. But wait, `demote_folio_list` checks `next_demotion_node` before proceeding. If that returns `NUMA_NO_NODE`, it bail early. Ok, that's a check.

The question then is, can we actually *trigger* this in a typical virtualized environment, like QEMU? We'd need to simulate a NUMA setup. But, QEMU can emulate NUMA nodes. We could set up multiple nodes and then try to trigger some memory tiering.

But hold on! Can `migrate_pages` *itself* be called directly with `MR_DEMOTION`? No, it looks like `MR_DEMOTION` is *only* used within `demote_folio_list`. That's important. I need to make sure I haven't missed anything, so I should double-check that `MR_DEMOTION` is used nowhere else in the kernel. Let's start with a check.

{
  "Expression": "MR_DEMOTION"
}

{
  "Output": "include/linux/migrate_mode.h=26=enum migrate_reason {\n--\ninclude/linux/migrate_mode.h-34-\tMR_LONGTERM_PIN,\ninclude/linux/migrate_mode.h:35:\tMR_DEMOTION,\ninclude/linux/migrate_mode.h-36-\tMR_DAMON,\n--\ninclude/trace/events/migrate.h-25-\tEM( MR_LONGTERM_PIN,\t\"longterm_pin\")\t\t\t\\\ninclude/trace/events/migrate.h:26:\tEM( MR_DEMOTION,\t\"demotion\")\t\t\t\\\ninclude/trace/events/migrate.h-27-\tEMe(MR_DAMON,\t\t\"damon\")\n--\nmm/migrate.c=1193=static void migrate_folio_done(struct folio *src,\n--\nmm/migrate.c-1195-{\nmm/migrate.c:1196:\tif (likely(!page_has_movable_ops(\u0026src-\u003epage)) \u0026\u0026 reason != MR_DEMOTION)\nmm/migrate.c-1197-\t\tmod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +\n--\nmm/migrate.c=2075=int migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n--\nmm/migrate.c-2088-\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\nmm/migrate.c:2089:\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\nmm/migrate.c-2090-\t\tmode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n--\nmm/vmscan.c=1021=static unsigned int demote_folio_list(struct list_head *demote_folios,\n--\nmm/vmscan.c-1037-\t\t.nmask = \u0026allowed_mask,\nmm/vmscan.c:1038:\t\t.reason = MR_DEMOTION,\nmm/vmscan.c-1039-\t};\n--\nmm/vmscan.c-1057-\tmigrate_pages(demote_folios, alloc_demote_folio, NULL,\nmm/vmscan.c:1058:\t\t      (unsigned long)\u0026mtc, MIGRATE_ASYNC, MR_DEMOTION,\nmm/vmscan.c-1059-\t\t      \u0026nr_succeeded);\n"
}

gemini-3.1-pro-preview

null

null

							input: 19394
							output: 23
							thoughts: 224
						

**Analyzing the Path to `migrate_pages` and Potential Vulnerabilities**

Okay, so I'm focused on this `demote_folio_list` function. Specifically, I'm trying to figure out if we can reach it from syzkaller. I know syzkaller runs in QEMU, and I can configure NUMA nodes in QEMU if I need to. But, default setups might not use multiple NUMA nodes.

But wait, the real target here is `migrate_pages` because that code path is reached if we can trigger `MR_DEMOTION`. That's where it all hinges.

I need to make sure there isn't another way to trigger `MIGRATE_ASYNC_NON_TEMPORAL_STORES`, so I can't just casually hit that flag. Nope, it's exclusively set within `migrate_pages`, and only when the `reason` is `MR_DEMOTION` and the `mode` is `MIGRATE_ASYNC`. Okay, that's good. But I'm going to double check.

Now, wait a second... `MIGRATE_ASYNC_NON_TEMPORAL_STORES` is a valid enum value. So could it be passed directly? No, I've confirmed that it's only set internally within `migrate_pages`. This is critical.

Alright, what about `copy_mc_to_kernel_nt`? Is *that* reachable from somewhere else? I need to check the call graph to be absolutely sure. Let's dig into that and see.

{
  "Expression": "copy_mc_to_kernel_nt"
}

{
  "Output": "arch/x86/include/asm/uaccess.h=497=unsigned long __must_check\narch/x86/include/asm/uaccess.h:498:copy_mc_to_kernel_nt(void *to, const void *from, unsigned len);\narch/x86/include/asm/uaccess.h:499:#define copy_mc_to_kernel_nt copy_mc_to_kernel_nt\narch/x86/include/asm/uaccess.h-500-\n--\narch/x86/lib/copy_mc.c=82=EXPORT_SYMBOL_GPL(copy_mc_to_kernel);\n--\narch/x86/lib/copy_mc.c-84-/**\narch/x86/lib/copy_mc.c:85: * copy_mc_to_kernel_nt - memory copy that handles source exceptions\narch/x86/lib/copy_mc.c-86- * if enabled, otherwise uses non-temporal stores\n--\narch/x86/lib/copy_mc.c-93- */\narch/x86/lib/copy_mc.c:94:unsigned long __must_check copy_mc_to_kernel_nt(void *dst, const void *src, unsigned len)\narch/x86/lib/copy_mc.c-95-{\n--\narch/x86/lib/copy_mc.c-107-}\narch/x86/lib/copy_mc.c:108:EXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt);\narch/x86/lib/copy_mc.c-109-\n--\ninclude/linux/highmem.h=453=static inline int copy_mc_highpage(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-471-\ninclude/linux/highmem.h:472:#ifdef copy_mc_to_kernel_nt\ninclude/linux/highmem.h-473-static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-479-\tvto = kmap_local_page(to);\ninclude/linux/highmem.h:480:\tret = copy_mc_to_kernel_nt(vto, vfrom, PAGE_SIZE);\ninclude/linux/highmem.h-481-\tif (!ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 20597
							output: 20
							thoughts: 110
						

**Analyzing the `copy_mc_highpage_nt` Function**

Okay, so I'm digging into this `copy_mc_highpage_nt` function. My initial thought process is to trace its usage. From what I can tell, it's exclusively called within `copy_mc_highpage_nt`, which in turn is called by `folio_mc_copy_nt`. And that leads me all the way back to `__migrate_folio`, specifically when the `mode` parameter is set to `MIGRATE_ASYNC_NON_TEMPORAL_STORES`. That's the crucial path.

Now the interesting thing is this entire chain seems to be tied to `MR_DEMOTION`. That's the real key to the situation. My question becomes: is memory demotion actually enabled by default within the kernel itself? That's what I need to establish. To figure that out I'll need to check the configuration options. I'll need to confirm whether `CONFIG_NUMA_BALANCING` or `CONFIG_MEMORY_TIERING` are enabled. That will tell me if we're dealing with a system that even has this feature available.

no matches

{
  "Expression": "config MEMORY_TIERING"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 20994
							output: 26
							thoughts: 14
						

Okay, here's my summary, tailored for an expert audience, as if I'm thinking these things myself:

**Tiering Configuration - Let's Dig In**

Alright, I need to get a handle on how this tiering is configured within the system. My first instinct is always to hit the `mm/Kconfig` file. That's the likely spot for the core options related to memory management and, specifically, tiering if it's been implemented with any degree of sophistication. I'm expecting to find conditional compilation options (`CONFIG_*` symbols) that enable or disable tiering, likely with some supporting options to control behavior, perhaps related to the characteristics of different memory tiers (speed, size, cost, etc.). I'll be looking for things that might control things such as whether we are caching data into faster tiers, migrating data around, or how we determine which data moves where. This initial check will probably give me a good lay of the land, providing the basic framework or structure around the tiering logic. Time to get this show on the road.

{
  "Expression": "MEMORY_TIERING",
  "PathPrefix": "mm/"
}

{
  "Output": "mm/memory-tiers.c=65=bool folio_use_access_time(struct folio *folio)\nmm/memory-tiers.c-66-{\nmm/memory-tiers.c:67:\treturn (sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING) \u0026\u0026\nmm/memory-tiers.c-68-\t       !node_is_toptier(folio_nid(folio));\n--\nmm/migrate.c=760=void folio_migrate_flags(struct folio *newfolio, struct folio *folio)\n--\nmm/migrate.c-805-\t */\nmm/migrate.c:806:\tif (sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING) {\nmm/migrate.c-807-\t\tbool f_toptier = node_is_toptier(folio_nid(folio));\n--\nmm/migrate.c=2665=int migrate_misplaced_folio_prepare(struct folio *folio,\n--\nmm/migrate.c-2695-\nmm/migrate.c:2696:\t\tif (!(sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING))\nmm/migrate.c-2697-\t\t\treturn -EAGAIN;\n--\nmm/migrate.c=2730=int migrate_misplaced_folio(struct folio *folio, int node)\n--\nmm/migrate.c-2747-\t\tcount_memcg_events(memcg, NUMA_PAGE_MIGRATE, nr_succeeded);\nmm/migrate.c:2748:\t\tif ((sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING)\nmm/migrate.c-2749-\t\t    \u0026\u0026 !node_is_toptier(folio_nid(folio))\n--\nmm/vmscan.c=4837=static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)\n--\nmm/vmscan.c-4852-\nmm/vmscan.c:4853:\tmark = sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING ?\nmm/vmscan.c-4854-\t       WMARK_PROMO : WMARK_HIGH;\n--\nmm/vmscan.c=6756=static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)\n--\nmm/vmscan.c-6769-\nmm/vmscan.c:6770:\t\tif (sysctl_numa_balancing_mode \u0026 NUMA_BALANCING_MEMORY_TIERING)\nmm/vmscan.c-6771-\t\t\tmark = promo_wmark_pages(zone);\n"
}

gemini-3.1-pro-preview

null

null

							input: 21962
							output: 32
							thoughts: 69
						

Okay, let's see what I'm thinking here.

**Deconstructing Memory Tiering in the Kernel**

Right, so I'm looking at `NUMA_BALANCING_MEMORY_TIERING`. My initial thought is that it's just another sysctl mode. Fine, that makes sense. But then I see `demote_folio_list` being called from `shrink_folio_list`. That's interesting. I know `shrink_folio_list` is key in managing memory pressure, which naturally leads me to memory tiering as well. So, to really understand this relationship, I need to understand when `demote_folio_list` is actually *called*. The next logical step is to dive into `shrink_folio_list` itself. I need to see what conditions trigger that function and then how it specifically utilizes `demote_folio_list`. That'll give me the full picture.

{
  "Expression": "demote_folio_list",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=986=static struct folio *alloc_demote_folio(struct folio *src,\n--\nmm/vmscan.c-1020- */\nmm/vmscan.c:1021:static unsigned int demote_folio_list(struct list_head *demote_folios,\nmm/vmscan.c-1022-\t\t\t\t      struct pglist_data *pgdat,\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1575-\t/* Migrate folios selected for demotion */\nmm/vmscan.c:1576:\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\nmm/vmscan.c-1577-\tnr_reclaimed += nr_demoted;\n"
}

gemini-3.1-pro-preview

null

null

							input: 22491
							output: 35
							thoughts: 21
						

Here's my analysis of the provided snippet, framed as my internal thought process:

**Deconstructing `shrink_folio_list` and `demote_folios`**

Alright, let's dive into this code. My immediate concern is how the `demote_folios` variable is being populated within the `shrink_folio_list` function. That's where the critical logic lies, the mechanism by which folios are being potentially down-graded or moved. I need to understand what factors influence the population of `demote_folios`. Are there certain criteria for folios to meet before they are considered candidates for demotion? Is this driven by size, frequency of access, a specific ordering scheme, or some other factor entirely? I'm going to carefully trace the data flow to uncover how this collection of folios is being built. The ultimate goal is understanding the algorithm's behavior. The way it identifies folios to `demote` is key to optimizing this function.

{
  "File": "mm/vmscan.c",
  "FirstLine": 1200,
  "LineCount": 50
}

{
  "Contents": "1200:\t\t\t *    folios are in writeback and there is nothing else to\n1201:\t\t\t *    reclaim. Wait for the writeback to complete.\n1202:\t\t\t *\n1203:\t\t\t * In cases 1) and 2) we activate the folios to get them out of\n1204:\t\t\t * the way while we continue scanning for clean folios on the\n1205:\t\t\t * inactive list and refilling from the active list. The\n1206:\t\t\t * observation here is that waiting for disk writes is more\n1207:\t\t\t * expensive than potentially causing reloads down the line.\n1208:\t\t\t * Since they're marked for immediate reclaim, they won't put\n1209:\t\t\t * memory pressure on the cache working set any longer than it\n1210:\t\t\t * takes to write them to disk.\n1211:\t\t\t */\n1212:\t\t\tif (folio_test_writeback(folio)) {\n1213:\t\t\t\tmapping = folio_mapping(folio);\n1214:\t\n1215:\t\t\t\t/* Case 1 above */\n1216:\t\t\t\tif (current_is_kswapd() \u0026\u0026\n1217:\t\t\t\t    folio_test_reclaim(folio) \u0026\u0026\n1218:\t\t\t\t    test_bit(PGDAT_WRITEBACK, \u0026pgdat-\u003eflags)) {\n1219:\t\t\t\t\tstat-\u003enr_immediate += nr_pages;\n1220:\t\t\t\t\tgoto activate_locked;\n1221:\t\n1222:\t\t\t\t/* Case 2 above */\n1223:\t\t\t\t} else if (writeback_throttling_sane(sc) ||\n1224:\t\t\t\t    !folio_test_reclaim(folio) ||\n1225:\t\t\t\t    !may_enter_fs(folio, sc-\u003egfp_mask) ||\n1226:\t\t\t\t    (mapping \u0026\u0026\n1227:\t\t\t\t     mapping_writeback_may_deadlock_on_reclaim(mapping))) {\n1228:\t\t\t\t\t/*\n1229:\t\t\t\t\t * This is slightly racy -\n1230:\t\t\t\t\t * folio_end_writeback() might have\n1231:\t\t\t\t\t * just cleared the reclaim flag, then\n1232:\t\t\t\t\t * setting the reclaim flag here ends up\n1233:\t\t\t\t\t * interpreted as the readahead flag - but\n1234:\t\t\t\t\t * that does not matter enough to care.\n1235:\t\t\t\t\t * What we do want is for this folio to\n1236:\t\t\t\t\t * have the reclaim flag set next time\n1237:\t\t\t\t\t * memcg reclaim reaches the tests above,\n1238:\t\t\t\t\t * so it will then wait for writeback to\n1239:\t\t\t\t\t * avoid OOM; and it's also appropriate\n1240:\t\t\t\t\t * in global reclaim.\n1241:\t\t\t\t\t */\n1242:\t\t\t\t\tfolio_set_reclaim(folio);\n1243:\t\t\t\t\tstat-\u003enr_writeback += nr_pages;\n1244:\t\t\t\t\tgoto activate_locked;\n1245:\t\n1246:\t\t\t\t/* Case 3 above */\n1247:\t\t\t\t} else {\n1248:\t\t\t\t\tfolio_unlock(folio);\n1249:\t\t\t\t\tfolio_wait_writeback(folio);\n"
}

gemini-3.1-pro-preview

null

null

							input: 23558
							output: 30
							thoughts: 20
						

Okay, here's my summary, taking on the persona you requested:

**Digging into `demote_folios`**

Alright, time to dive in. I need to understand what's happening with `demote_folios`, so my first move is to pinpoint its location in the kernel. Let's see...I'll start by searching for `demote_folios` specifically within `mm/vmscan.c`. That seems the most likely place, given my existing knowledge of memory management and scanning processes. This targeted search should give me a good jumping-off point to grasp its context and functionality. With any luck, it's a relatively straightforward function. I'm hoping I can quickly identify the key variables it operates on, the conditions that trigger its execution, and its overall impact on the system's memory management.

{
  "Expression": "demote_folios",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=986=static struct folio *alloc_demote_folio(struct folio *src,\n--\nmm/vmscan.c-1017-/*\nmm/vmscan.c:1018: * Take folios on @demote_folios and attempt to demote them to another node.\nmm/vmscan.c:1019: * Folios which are not demoted are left on @demote_folios.\nmm/vmscan.c-1020- */\nmm/vmscan.c:1021:static unsigned int demote_folio_list(struct list_head *demote_folios,\nmm/vmscan.c-1022-\t\t\t\t      struct pglist_data *pgdat,\n--\nmm/vmscan.c-1040-\nmm/vmscan.c:1041:\tif (list_empty(demote_folios))\nmm/vmscan.c-1042-\t\treturn 0;\n--\nmm/vmscan.c-1056-\t/* Demotion ignores all cpuset and mempolicy settings */\nmm/vmscan.c:1057:\tmigrate_pages(demote_folios, alloc_demote_folio, NULL,\nmm/vmscan.c-1058-\t\t      (unsigned long)\u0026mtc, MIGRATE_ASYNC, MR_DEMOTION,\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1089-\tLIST_HEAD(ret_folios);\nmm/vmscan.c:1090:\tLIST_HEAD(demote_folios);\nmm/vmscan.c-1091-\tunsigned int nr_reclaimed = 0, nr_demoted = 0;\n--\nmm/vmscan.c-1275-\t\t    (thp_migration_supported() || !folio_test_large(folio))) {\nmm/vmscan.c:1276:\t\t\tlist_add(\u0026folio-\u003elru, \u0026demote_folios);\nmm/vmscan.c-1277-\t\t\tfolio_unlock(folio);\n--\nmm/vmscan.c-1575-\t/* Migrate folios selected for demotion */\nmm/vmscan.c:1576:\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\nmm/vmscan.c-1577-\tnr_reclaimed += nr_demoted;\nmm/vmscan.c-1578-\tstat-\u003enr_demoted += nr_demoted;\nmm/vmscan.c:1579:\t/* Folios that could not be demoted are still in @demote_folios */\nmm/vmscan.c:1580:\tif (!list_empty(\u0026demote_folios)) {\nmm/vmscan.c-1581-\t\t/* Folios which weren't demoted go back on @folio_list */\nmm/vmscan.c:1582:\t\tlist_splice_init(\u0026demote_folios, folio_list);\nmm/vmscan.c-1583-\n"
}

gemini-3.1-pro-preview

null

null

							input: 24565
							output: 35
							thoughts: 14
						

Okay, here's my understanding, tailored for an expert audience, and written as a first-person summary of the described thought process:

**Diving into the Code: Line 1275**

Alright, I need to get my bearings and understand the current state of this system. I'm focusing in on the logic around line 1275, let's take a look there. My hypothesis is that a condition there is causing the issue I'm seeing and I need to assess the surrounding code to grasp the context. Let's see what that condition *actually* says, how it evaluates, and the consequences of its evaluation. Hopefully, I can pick up enough context just from that section.

{
  "File": "mm/vmscan.c",
  "FirstLine": 1260,
  "LineCount": 30
}

{
  "Contents": "1260:\t\t\tcase FOLIOREF_ACTIVATE:\n1261:\t\t\t\tgoto activate_locked;\n1262:\t\t\tcase FOLIOREF_KEEP:\n1263:\t\t\t\tstat-\u003enr_ref_keep += nr_pages;\n1264:\t\t\t\tgoto keep_locked;\n1265:\t\t\tcase FOLIOREF_RECLAIM:\n1266:\t\t\tcase FOLIOREF_RECLAIM_CLEAN:\n1267:\t\t\t\t; /* try to reclaim the folio below */\n1268:\t\t\t}\n1269:\t\n1270:\t\t\t/*\n1271:\t\t\t * Before reclaiming the folio, try to relocate\n1272:\t\t\t * its contents to another node.\n1273:\t\t\t */\n1274:\t\t\tif (do_demote_pass \u0026\u0026\n1275:\t\t\t    (thp_migration_supported() || !folio_test_large(folio))) {\n1276:\t\t\t\tlist_add(\u0026folio-\u003elru, \u0026demote_folios);\n1277:\t\t\t\tfolio_unlock(folio);\n1278:\t\t\t\tcontinue;\n1279:\t\t\t}\n1280:\t\n1281:\t\t\t/*\n1282:\t\t\t * Anonymous process memory has backing store?\n1283:\t\t\t * Try to allocate it some swap space here.\n1284:\t\t\t * Lazyfree folio could be freed directly\n1285:\t\t\t */\n1286:\t\t\tif (folio_test_anon(folio) \u0026\u0026 folio_test_swapbacked(folio) \u0026\u0026\n1287:\t\t\t\t\t!folio_test_swapcache(folio)) {\n1288:\t\t\t\tif (!(sc-\u003egfp_mask \u0026 __GFP_IO))\n1289:\t\t\t\t\tgoto keep_locked;\n"
}

gemini-3.1-pro-preview

null

null

							input: 25203
							output: 32
							thoughts: 27
						

Okay, here's my interpretation of that thought process, assuming I'm an expert in this field, and speaking from the first person perspective:

**Investigating the Demotion Pass**

Alright, I see we're at a point where `do_demote_pass` is being checked. My immediate thought is, "Okay, we're demoting *something*. This is a critical point. Now, the key here is, I need to understand *why* this pass is happening and what conditions are triggering it." So, my mind immediately jumps to the question of *how* `do_demote_pass` got set in the first place. I need to trace back through the code, find the assignment or conditional logic that determines the value of that variable. Is it based on certain data characteristics? Algorithm parameters? Specific states of the execution? That's what I need to figure out. I need to understand the causal link. The goal is to fully understand the circumstances under which the demotion pass is active, so I can ensure it's behaving as expected.

{
  "Expression": "do_demote_pass",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1092-\tunsigned int pgactivate = 0;\nmm/vmscan.c:1093:\tbool do_demote_pass;\nmm/vmscan.c-1094-\tstruct swap_iocb *plug = NULL;\n--\nmm/vmscan.c-1098-\tcond_resched();\nmm/vmscan.c:1099:\tdo_demote_pass = can_demote(pgdat-\u003enode_id, sc, memcg);\nmm/vmscan.c-1100-\n--\nmm/vmscan.c-1273-\t\t */\nmm/vmscan.c:1274:\t\tif (do_demote_pass \u0026\u0026\nmm/vmscan.c-1275-\t\t    (thp_migration_supported() || !folio_test_large(folio))) {\n--\nmm/vmscan.c-1600-\t\tif (!sc-\u003eproactive) {\nmm/vmscan.c:1601:\t\t\tdo_demote_pass = false;\nmm/vmscan.c-1602-\t\t\tgoto retry;\n"
}

gemini-3.1-pro-preview

null

null

							input: 25810
							output: 30
							thoughts: 10
						

Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:

**Checking `can_demote`**

Alright, before I proceed with any user role modifications, I need to verify a fundamental condition: can this particular user be demoted? This isn't just a generic permission check; it likely involves more nuanced logic. I'm thinking about potential implications here. Are there dependencies on their current role? Are there any data integrity concerns if their access level is reduced? Are there any specific contractual obligations or internal policies I need to account for?

I need to make sure `can_demote` function accounts for all of these things.

{
  "Expression": "can_demote",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=307=static void flush_reclaim_state(struct scan_control *sc)\n--\nmm/vmscan.c-342-\nmm/vmscan.c:343:static bool can_demote(int nid, struct scan_control *sc,\nmm/vmscan.c-344-\t\t       struct mem_cgroup *memcg)\n--\nmm/vmscan.c=363=static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,\n--\nmm/vmscan.c-384-\t */\nmm/vmscan.c:385:\treturn can_demote(nid, sc, memcg);\nmm/vmscan.c-386-}\n--\nmm/vmscan.c=1083=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1098-\tcond_resched();\nmm/vmscan.c:1099:\tdo_demote_pass = can_demote(pgdat-\u003enode_id, sc, memcg);\nmm/vmscan.c-1100-\n--\nmm/vmscan.c=2647=static bool can_age_anon_pages(struct lruvec *lruvec,\n--\nmm/vmscan.c-2654-\t/* Also valuable if anon pages can be demoted: */\nmm/vmscan.c:2655:\treturn can_demote(lruvec_pgdat(lruvec)-\u003enode_id, sc,\nmm/vmscan.c-2656-\t\t\t  lruvec_memcg(lruvec));\n--\nmm/vmscan.c=2730=static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc)\n--\nmm/vmscan.c-2737-\nmm/vmscan.c:2738:\tif (!can_demote(pgdat-\u003enode_id, sc, memcg) \u0026\u0026\nmm/vmscan.c-2739-\t    mem_cgroup_get_nr_swap_pages(memcg) \u003c MIN_LRU_BATCH)\n"
}

gemini-3.1-pro-preview

null

null

							input: 26548
							output: 34
							thoughts: 12
						

Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:

**Analyzing the Demotion Logic**

Alright, the focus is on the `can_demote` implementation. I need to understand the constraints and conditions that govern when something can be demoted. The function signature and any associated documentation are crucial here. I'll need to dissect the code to grasp the underlying logic. Are there specific roles, states, or permissions involved? Are there edge cases I should be aware of, perhaps related to cascading demotions or data integrity? I'm looking for the core principles that dictate whether a demotion is permissible. I'll probably start by identifying any preconditions the function checks before allowing a demotion to proceed. Then, I'll need to think about the post-demotion implications – what happens to related data, permissions, or dependencies? Are there any potential vulnerabilities or logical flaws in the process? This investigation should unveil the criteria and implications of a demotion.

{
  "File": "mm/vmscan.c",
  "FirstLine": 340,
  "LineCount": 30
}

{
  "Contents": " 340:\t\t}\n 341:\t}\n 342:\t\n 343:\tstatic bool can_demote(int nid, struct scan_control *sc,\n 344:\t\t\t       struct mem_cgroup *memcg)\n 345:\t{\n 346:\t\tstruct pglist_data *pgdat = NODE_DATA(nid);\n 347:\t\tnodemask_t allowed_mask;\n 348:\t\n 349:\t\tif (!pgdat || !numa_demotion_enabled)\n 350:\t\t\treturn false;\n 351:\t\tif (sc \u0026\u0026 sc-\u003eno_demotion)\n 352:\t\t\treturn false;\n 353:\t\n 354:\t\tnode_get_allowed_targets(pgdat, \u0026allowed_mask);\n 355:\t\tif (nodes_empty(allowed_mask))\n 356:\t\t\treturn false;\n 357:\t\n 358:\t\t/* Filter out nodes that are not in cgroup's mems_allowed. */\n 359:\t\tmem_cgroup_node_filter_allowed(memcg, \u0026allowed_mask);\n 360:\t\treturn !nodes_empty(allowed_mask);\n 361:\t}\n 362:\t\n 363:\tstatic inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,\n 364:\t\t\t\t\t\t  int nid,\n 365:\t\t\t\t\t\t  struct scan_control *sc)\n 366:\t{\n 367:\t\tif (memcg == NULL) {\n 368:\t\t\t/*\n 369:\t\t\t * For non-memcg reclaim, is there\n"
}

gemini-3.1-pro-preview

null

null

							input: 27245
							output: 21
							thoughts: 31
						

Okay, here's my take on those thoughts, framed from my perspective:

**Debugging NUMA Demotion**

Alright, the first thing I need to confirm is that `numa_demotion_enabled` is actually set to true. Seems obvious, but you have to start somewhere, and a quick sanity check never hurts. Now, where is this flag being initialized and/or modified? I need to trace back its path to see what could potentially be influencing it. Let's dig into the code and see where `numa_demotion_enabled` is declared and if there is any assignment or manipulation of the variable. I need to understand its lifecycle to see what might be happening during execution.

{
  "Expression": "numa_demotion_enabled"
}

{
  "Output": "include/linux/memory-tiers.h=36=struct access_coordinate;\n--\ninclude/linux/memory-tiers.h-38-#ifdef CONFIG_NUMA\ninclude/linux/memory-tiers.h:39:extern bool numa_demotion_enabled;\ninclude/linux/memory-tiers.h-40-extern struct memory_dev_type *default_dram_type;\n--\ninclude/linux/memory-tiers.h=70=static inline bool node_is_toptier(int node)\n--\ninclude/linux/memory-tiers.h-77-\ninclude/linux/memory-tiers.h:78:#define numa_demotion_enabled\tfalse\ninclude/linux/memory-tiers.h-79-#define default_dram_type\tNULL\n--\nmm/memory-tiers.c=937=subsys_initcall(memory_tier_init);\nmm/memory-tiers.c-938-\nmm/memory-tiers.c:939:bool numa_demotion_enabled = false;\nmm/memory-tiers.c-940-\n--\nmm/memory-tiers.c=943=static ssize_t demotion_enabled_show(struct kobject *kobj,\n--\nmm/memory-tiers.c-945-{\nmm/memory-tiers.c:946:\treturn sysfs_emit(buf, \"%s\\n\", str_true_false(numa_demotion_enabled));\nmm/memory-tiers.c-947-}\n--\nmm/memory-tiers.c=949=static ssize_t demotion_enabled_store(struct kobject *kobj,\n--\nmm/memory-tiers.c-953-\tssize_t ret;\nmm/memory-tiers.c:954:\tbool before = numa_demotion_enabled;\nmm/memory-tiers.c-955-\nmm/memory-tiers.c:956:\tret = kstrtobool(buf, \u0026numa_demotion_enabled);\nmm/memory-tiers.c-957-\tif (ret)\n--\nmm/memory-tiers.c-963-\t */\nmm/memory-tiers.c:964:\tif (before == false \u0026\u0026 numa_demotion_enabled == true) {\nmm/memory-tiers.c-965-\t\tstruct pglist_data *pgdat;\n--\nmm/memory-tiers.c-973-\nmm/memory-tiers.c:974:static struct kobj_attribute numa_demotion_enabled_attr =\nmm/memory-tiers.c-975-\t__ATTR_RW(demotion_enabled);\n--\nmm/memory-tiers.c=977=static struct attribute *numa_attrs[] = {\nmm/memory-tiers.c:978:\t\u0026numa_demotion_enabled_attr.attr,\nmm/memory-tiers.c-979-\tNULL,\n--\nmm/vmscan.c=343=static bool can_demote(int nid, struct scan_control *sc,\n--\nmm/vmscan.c-348-\nmm/vmscan.c:349:\tif (!pgdat || !numa_demotion_enabled)\nmm/vmscan.c-350-\t\treturn false;\n"
}

gemini-3.1-pro-preview

null

null

							input: 28254
							output: 35
							thoughts: 134
						

**Analyzing the `numa_demotion_enabled` Flag**

Okay, so the `numa_demotion_enabled` flag is false by default. Right, that makes sense. Hmm, I know it can be enabled through the `demotion_enabled` entry in sysfs. But wait a minute... if it's off by default, the syzkaller fuzzer won't trigger this functionality unless it explicitly writes to that `/sys/kernel/mm/numa/demotion_enabled` file, which is the mechanism to change the flag. I need to make sure this is actually getting tested.

Does syzkaller target sysfs at all? Yes, it's capable of sysfs fuzzing, that's certain, but is it guaranteed to enable *this* particular flag? Probably not, as it may be targeting other sysfs entries, or have a random generation of sysfs calls, or be testing different kernel versions. It's not a sure thing. So, I need to know if there's any other way this `numa_demotion_enabled` flag can become true, any other code path that would change the value. Let me dig into the source... Let's start with `mm/memory-tiers.c`. That seems like the logical place to start.

{
  "Expression": "numa_demotion_enabled =",
  "PathPrefix": "mm/memory-tiers.c"
}

{
  "Output": "mm/memory-tiers.c=937=subsys_initcall(memory_tier_init);\nmm/memory-tiers.c-938-\nmm/memory-tiers.c:939:bool numa_demotion_enabled = false;\nmm/memory-tiers.c-940-\n--\nmm/memory-tiers.c=949=static ssize_t demotion_enabled_store(struct kobject *kobj,\n--\nmm/memory-tiers.c-963-\t */\nmm/memory-tiers.c:964:\tif (before == false \u0026\u0026 numa_demotion_enabled == true) {\nmm/memory-tiers.c-965-\t\tstruct pglist_data *pgdat;\n"
}

gemini-3.1-pro-preview

null

null

							input: 28889
							output: 34
							thoughts: 47
						

Okay, let's see...

**Investigating Automatic NUMA Demotion**

Hmm, I seem to recall something about `numa_demotion_enabled` possibly being activated automatically, maybe if there's some kind of persistent memory involved? I should verify that. I need to get a clearer understanding of the conditions that trigger this feature. Right, the code for memory tiers would be the place to look for that logic. I'll need to go to `mm/memory-tiers.c` and dig into the implementation details of `numa_demotion_enabled`. I'll start with a quick search within that file, see what I can find.

{
  "Expression": "numa_demotion_enabled",
  "PathPrefix": "mm/memory-tiers.c"
}

{
  "Output": "mm/memory-tiers.c=937=subsys_initcall(memory_tier_init);\nmm/memory-tiers.c-938-\nmm/memory-tiers.c:939:bool numa_demotion_enabled = false;\nmm/memory-tiers.c-940-\n--\nmm/memory-tiers.c=943=static ssize_t demotion_enabled_show(struct kobject *kobj,\n--\nmm/memory-tiers.c-945-{\nmm/memory-tiers.c:946:\treturn sysfs_emit(buf, \"%s\\n\", str_true_false(numa_demotion_enabled));\nmm/memory-tiers.c-947-}\n--\nmm/memory-tiers.c=949=static ssize_t demotion_enabled_store(struct kobject *kobj,\n--\nmm/memory-tiers.c-953-\tssize_t ret;\nmm/memory-tiers.c:954:\tbool before = numa_demotion_enabled;\nmm/memory-tiers.c-955-\nmm/memory-tiers.c:956:\tret = kstrtobool(buf, \u0026numa_demotion_enabled);\nmm/memory-tiers.c-957-\tif (ret)\n--\nmm/memory-tiers.c-963-\t */\nmm/memory-tiers.c:964:\tif (before == false \u0026\u0026 numa_demotion_enabled == true) {\nmm/memory-tiers.c-965-\t\tstruct pglist_data *pgdat;\n--\nmm/memory-tiers.c-973-\nmm/memory-tiers.c:974:static struct kobj_attribute numa_demotion_enabled_attr =\nmm/memory-tiers.c-975-\t__ATTR_RW(demotion_enabled);\n--\nmm/memory-tiers.c=977=static struct attribute *numa_attrs[] = {\nmm/memory-tiers.c:978:\t\u0026numa_demotion_enabled_attr.attr,\nmm/memory-tiers.c-979-\tNULL,\n"
}

gemini-3.1-pro-preview

null

null

							input: 29646
							output: 22
							thoughts: 41
						

**Investigating NUMA Demotion Settings**

Okay, so it looks like the current setting is only accessible and modifiable through the `sysfs` filesystem. That's... interesting. I'm wondering if this is the *only* place it's managed. It would be a bit of a surprise if there weren't other potential control points or configuration files. I need to make sure I haven't missed something crucial. Let me quickly scan the system for any other instances where `numa_demotion_enabled` might be defined or set to "true". I want to be thorough and confirm this assumption. I'll need to double-check my understanding of how this feature is configured on this particular platform.

{
  "Expression": "numa_demotion_enabled ="
}

{
  "Output": "mm/memory-tiers.c=937=subsys_initcall(memory_tier_init);\nmm/memory-tiers.c-938-\nmm/memory-tiers.c:939:bool numa_demotion_enabled = false;\nmm/memory-tiers.c-940-\n--\nmm/memory-tiers.c=949=static ssize_t demotion_enabled_store(struct kobject *kobj,\n--\nmm/memory-tiers.c-963-\t */\nmm/memory-tiers.c:964:\tif (before == false \u0026\u0026 numa_demotion_enabled == true) {\nmm/memory-tiers.c-965-\t\tstruct pglist_data *pgdat;\n"
}

gemini-3.1-pro-preview

null

null

							input: 30049
							output: 35
							thoughts: 44
						

Okay, let me think this through.

**Investigating Potential Default Tiering Configuration**

Wait a minute, I think I might have an idea. In `mm/memory-tiers.c`, isn't there a possibility that the multi-tier configuration flag is actually set to true by *default* if the system detects multiple memory tiers? It would make sense. Let's dig into that... I need to look closer at the initialization routine, something like `memory_tier_init`, or a similarly named function, to confirm whether or not this is the case and how it's handled. That should clarify this.

{
  "File": "mm/memory-tiers.c",
  "FirstLine": 900,
  "LineCount": 50
}

{
  "Contents": " 900:\t\t\tbreak;\n 901:\t\t}\n 902:\t\n 903:\t\treturn notifier_from_errno(0);\n 904:\t}\n 905:\t\n 906:\tstatic int __init memory_tier_init(void)\n 907:\t{\n 908:\t\tint ret;\n 909:\t\n 910:\t\tret = subsys_virtual_register(\u0026memory_tier_subsys, NULL);\n 911:\t\tif (ret)\n 912:\t\t\tpanic(\"%s() failed to register memory tier subsystem\\n\", __func__);\n 913:\t\n 914:\t#ifdef CONFIG_MIGRATION\n 915:\t\tnode_demotion = kzalloc_objs(struct demotion_nodes, nr_node_ids);\n 916:\t\tWARN_ON(!node_demotion);\n 917:\t#endif\n 918:\t\n 919:\t\tmutex_lock(\u0026memory_tier_lock);\n 920:\t\t/*\n 921:\t\t * For now we can have 4 faster memory tiers with smaller adistance\n 922:\t\t * than default DRAM tier.\n 923:\t\t */\n 924:\t\tdefault_dram_type = mt_find_alloc_memory_type(MEMTIER_ADISTANCE_DRAM,\n 925:\t\t\t\t\t\t\t      \u0026default_memory_types);\n 926:\t\tmutex_unlock(\u0026memory_tier_lock);\n 927:\t\tif (IS_ERR(default_dram_type))\n 928:\t\t\tpanic(\"%s() failed to allocate default DRAM tier\\n\", __func__);\n 929:\t\n 930:\t\t/* Record nodes with memory and CPU to set default DRAM performance. */\n 931:\t\tnodes_and(default_dram_nodes, node_states[N_MEMORY],\n 932:\t\t\t  node_states[N_CPU]);\n 933:\t\n 934:\t\thotplug_node_notifier(memtier_hotplug_callback, MEMTIER_HOTPLUG_PRI);\n 935:\t\treturn 0;\n 936:\t}\n 937:\tsubsys_initcall(memory_tier_init);\n 938:\t\n 939:\tbool numa_demotion_enabled = false;\n 940:\t\n 941:\t#ifdef CONFIG_MIGRATION\n 942:\t#ifdef CONFIG_SYSFS\n 943:\tstatic ssize_t demotion_enabled_show(struct kobject *kobj,\n 944:\t\t\t\t\t     struct kobj_attribute *attr, char *buf)\n 945:\t{\n 946:\t\treturn sysfs_emit(buf, \"%s\\n\", str_true_false(numa_demotion_enabled));\n 947:\t}\n 948:\t\n 949:\tstatic ssize_t demotion_enabled_store(struct kobject *kobj,\n"
}

gemini-3.1-pro-preview

null

null

							input: 31020
							output: 23
							thoughts: 89
						

**Investigating Potential `copy_mc_to_kernel_nt` Triggers**

Okay, so I'm digging into this code and it looks like `numa_demotion_enabled` is disabled by default. That's the baseline, pretty standard. But then a thought hits me – syzkaller. It's fuzzing sysfs, right? Specifically, it's capable of writing to `/sys/kernel/mm/numa/demotion_enabled`. So, that's one potential path to changing the default and, by extension, triggering related code paths. I need to keep that in mind.

Now, the core question is whether that's the *only* way to get to `copy_mc_to_kernel_nt`. It seems like a pretty specific function, and I doubt it's called willy-nilly. Time to do a quick code dive. I'll search the codebase to see if `copy_mc_to_kernel_nt` is used anywhere else. That'll be crucial to understand the function's potential exposure and how it might be exercised. Knowing all potential call sites will give me a comprehensive picture of potential vulnerabilities and how to trigger them.

{
  "Expression": "copy_mc_to_kernel_nt"
}

{
  "Output": "arch/x86/include/asm/uaccess.h=497=unsigned long __must_check\narch/x86/include/asm/uaccess.h:498:copy_mc_to_kernel_nt(void *to, const void *from, unsigned len);\narch/x86/include/asm/uaccess.h:499:#define copy_mc_to_kernel_nt copy_mc_to_kernel_nt\narch/x86/include/asm/uaccess.h-500-\n--\narch/x86/lib/copy_mc.c=82=EXPORT_SYMBOL_GPL(copy_mc_to_kernel);\n--\narch/x86/lib/copy_mc.c-84-/**\narch/x86/lib/copy_mc.c:85: * copy_mc_to_kernel_nt - memory copy that handles source exceptions\narch/x86/lib/copy_mc.c-86- * if enabled, otherwise uses non-temporal stores\n--\narch/x86/lib/copy_mc.c-93- */\narch/x86/lib/copy_mc.c:94:unsigned long __must_check copy_mc_to_kernel_nt(void *dst, const void *src, unsigned len)\narch/x86/lib/copy_mc.c-95-{\n--\narch/x86/lib/copy_mc.c-107-}\narch/x86/lib/copy_mc.c:108:EXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt);\narch/x86/lib/copy_mc.c-109-\n--\ninclude/linux/highmem.h=453=static inline int copy_mc_highpage(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-471-\ninclude/linux/highmem.h:472:#ifdef copy_mc_to_kernel_nt\ninclude/linux/highmem.h-473-static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-479-\tvto = kmap_local_page(to);\ninclude/linux/highmem.h:480:\tret = copy_mc_to_kernel_nt(vto, vfrom, PAGE_SIZE);\ninclude/linux/highmem.h-481-\tif (!ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 32004
							output: 22
							thoughts: 30
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, presented in the first person:

**Focusing on a Specific Function**

Alright, so the clue here is that this specific piece of logic is only referenced within `copy_mc_highpage_nt`. That's the key. My first move will be to dive into the implementation of `copy_mc_highpage_nt` and understand precisely how and why it's using the code in question. This strongly suggests the answer lies within the context of that function, the assumptions it makes, and the data it operates on. Knowing *how* it's used is half the battle in understanding *why* it exists in the first place. This narrowing of focus allows me to quickly home in on the relevant section of the codebase and its role in the greater scheme of things.

{
  "Expression": "copy_mc_highpage_nt"
}

{
  "Output": "include/linux/highmem.h=453=static inline int copy_mc_highpage(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-472-#ifdef copy_mc_to_kernel_nt\ninclude/linux/highmem.h:473:static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\ninclude/linux/highmem.h-474-{\n--\ninclude/linux/highmem.h-491-#else\ninclude/linux/highmem.h:492:static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\ninclude/linux/highmem.h-493-{\n--\ninclude/linux/highmem.h=505=static inline int copy_mc_highpage(struct page *to, struct page *from)\n--\ninclude/linux/highmem.h-510-\ninclude/linux/highmem.h:511:static inline int copy_mc_highpage_nt(struct page *to, struct page *from)\ninclude/linux/highmem.h-512-{\n--\nmm/util.c=752=int folio_mc_copy_nt(struct folio *dst, struct folio *src)\n--\nmm/util.c-757-\tfor (;;) {\nmm/util.c:758:\t\tif (copy_mc_highpage_nt(folio_page(dst, i), folio_page(src, i)))\nmm/util.c-759-\t\t\treturn -EHWPOISON;\n"
}

gemini-3.1-pro-preview

null

null

							input: 32634
							output: 21
							thoughts: 28
						

Okay, here's my take on those thoughts, framed as an expert's inner monologue:

**Focusing on `folio_mc_copy_nt`**

Alright, so the clue is that this function, whatever it is, is *only* used in `folio_mc_copy_nt`. That's a pretty significant constraint. It means any deeper investigation should naturally start there. Let's see what we're dealing with in that function; the context is going to be key to understanding the purpose and potential issues. Let me go take a look at it...

{
  "Expression": "folio_mc_copy_nt"
}

{
  "Output": "include/linux/mm.h=1646=int folio_mc_copy(struct folio *dst, struct folio *src);\ninclude/linux/mm.h:1647:int folio_mc_copy_nt(struct folio *dst, struct folio *src);\ninclude/linux/mm.h-1648-\n--\nmm/migrate.c=855=static int __migrate_folio(struct address_space *mapping, struct folio *dst,\n--\nmm/migrate.c-865-\tif (mode == MIGRATE_ASYNC_NON_TEMPORAL_STORES)\nmm/migrate.c:866:\t\trc = folio_mc_copy_nt(dst, src);\nmm/migrate.c-867-\telse\n--\nmm/util.c=750=EXPORT_SYMBOL(folio_mc_copy);\nmm/util.c-751-\nmm/util.c:752:int folio_mc_copy_nt(struct folio *dst, struct folio *src)\nmm/util.c-753-{\n--\nmm/util.c-766-}\nmm/util.c:767:EXPORT_SYMBOL(folio_mc_copy_nt);\nmm/util.c-768-\n"
}

gemini-3.1-pro-preview

null

null

							input: 33121
							output: 18
							thoughts: 22
						

Okay, here's my interpretation of those thoughts, crafted with the understanding that I'm speaking to a fellow expert:

**Narrowing the Focus: Understanding Folio Migration**

Alright, I'm zeroing in on this `__migrate_folio` function. The code's usage is pretty limited, isn't it? Just the one instance mentioned. That's good, that simplifies things a bit. So, the question becomes, what exactly *is* going on within `__migrate_folio`? Given the naming, I'm guessing it handles some kind of data transition or update, probably related to a folio or series of folios, but I need to dig deeper. Let's get into it and see what we're really dealing with in there.

{
  "Expression": "__migrate_folio"
}

{
  "Output": "mm/migrate.c=849=EXPORT_SYMBOL(folio_migrate_flags);\n--\nmm/migrate.c-854-\nmm/migrate.c:855:static int __migrate_folio(struct address_space *mapping, struct folio *dst,\nmm/migrate.c-856-\t\t\t   struct folio *src, void *src_private,\n--\nmm/migrate.c=895=int migrate_folio(struct address_space *mapping, struct folio *dst,\n--\nmm/migrate.c-898-\tBUG_ON(folio_test_writeback(src));\t/* Writeback must be complete */\nmm/migrate.c:899:\treturn __migrate_folio(mapping, dst, src, NULL, mode);\nmm/migrate.c-900-}\n--\nmm/migrate.c=1052=int filemap_migrate_folio(struct address_space *mapping,\n--\nmm/migrate.c-1054-{\nmm/migrate.c:1055:\treturn __migrate_folio(mapping, dst, src, folio_get_private(src), mode);\nmm/migrate.c-1056-}\n--\nmm/migrate.c=1138=enum {\n--\nmm/migrate.c-1143-\nmm/migrate.c:1144:static void __migrate_folio_record(struct folio *dst,\nmm/migrate.c-1145-\t\t\t\t   int old_page_state,\n--\nmm/migrate.c-1150-\nmm/migrate.c:1151:static void __migrate_folio_extract(struct folio *dst,\nmm/migrate.c-1152-\t\t\t\t   int *old_page_state,\n--\nmm/migrate.c=1206=static int migrate_folio_unmap(new_folio_t get_new_folio,\n--\nmm/migrate.c-1305-\tif (unlikely(page_has_movable_ops(\u0026src-\u003epage))) {\nmm/migrate.c:1306:\t\t__migrate_folio_record(dst, old_page_state, anon_vma);\nmm/migrate.c-1307-\t\treturn 0;\n--\nmm/migrate.c-1335-\tif (!folio_mapped(src)) {\nmm/migrate.c:1336:\t\t__migrate_folio_record(dst, old_page_state, anon_vma);\nmm/migrate.c-1337-\t\treturn 0;\n--\nmm/migrate.c=1356=static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,\n--\nmm/migrate.c-1365-\nmm/migrate.c:1366:\t__migrate_folio_extract(dst, \u0026old_page_state, \u0026anon_vma);\nmm/migrate.c-1367-\tprev = dst-\u003elru.prev;\n--\nmm/migrate.c-1425-\t\tlist_add(\u0026dst-\u003elru, prev);\nmm/migrate.c:1426:\t\t__migrate_folio_record(dst, old_page_state, anon_vma);\nmm/migrate.c-1427-\t\treturn rc;\n--\nmm/migrate.c=1754=static void migrate_folios_undo(struct list_head *src_folios,\n--\nmm/migrate.c-1766-\nmm/migrate.c:1767:\t\t__migrate_folio_extract(dst, \u0026old_page_state, \u0026anon_vma);\nmm/migrate.c-1768-\t\tmigrate_folio_undo_src(folio, old_page_state \u0026 PAGE_WAS_MAPPED,\n"
}

gemini-3.1-pro-preview

null

null

							input: 34248
							output: 17
							thoughts: 44
						

Okay, let's see what's going on here.

**Deconstructing the `migrate_folio` Call Chain**

Right, so `__migrate_folio` is definitely a core component of this migration process, as it is called by both `migrate_folio` and `filemap_migrate_folio`. It's good practice to understand the call graph, as you know. The relationship between these functions is key to understanding how data is actually moved around and managed at the folio level.

The logical next step is to trace back and identify all the calling functions. Finding all the calls to both `migrate_folio` and `filemap_migrate_folio` will give a comprehensive picture of how this migration is initiated and integrated within the broader system. I need to understand what's triggering these migration operations to grasp the complete workflow.

{
  "Expression": "migrate_folio"
}

{
  "Output": "\nFull output is too long, showing 500 out of 824 lines.\nUse more precise expression if possible.\n\nDocumentation/filesystems/locking.rst=245=prototypes::\n--\nDocumentation/filesystems/locking.rst-261-\tint (*direct_IO)(struct kiocb *, struct iov_iter *iter);\nDocumentation/filesystems/locking.rst:262:\tint (*migrate_folio)(struct address_space *, struct folio *dst,\nDocumentation/filesystems/locking.rst-263-\t\t\tstruct folio *src, enum migrate_mode);\n--\nDocumentation/filesystems/locking.rst=287=direct_IO:\nDocumentation/filesystems/locking.rst:288:migrate_folio:\t\tyes (both)\nDocumentation/filesystems/locking.rst-289-launder_folio:\t\tyes\n--\nDocumentation/filesystems/vfs.rst=749=cache in your filesystem.  The following members are defined:\n--\nDocumentation/filesystems/vfs.rst-768-\t\tssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);\nDocumentation/filesystems/vfs.rst:769:\t\tint (*migrate_folio)(struct mapping *, struct folio *dst,\nDocumentation/filesystems/vfs.rst-770-\t\t\t\tstruct folio *src, enum migrate_mode);\n--\nDocumentation/filesystems/vfs.rst-937-\nDocumentation/filesystems/vfs.rst:938:``migrate_folio``\nDocumentation/filesystems/vfs.rst-939-\tThis is used to compact the physical memory usage.  If the VM\n--\nDocumentation/filesystems/vfs.rst-941-\tsignalling imminent failure) it will pass a new folio and an old\nDocumentation/filesystems/vfs.rst:942:\tfolio to this function.  migrate_folio should transfer any private\nDocumentation/filesystems/vfs.rst-943-\tdata across and update any references that it has to the folio.\n--\nblock/fops.c=524=const struct address_space_operations def_blk_aops = {\n--\nblock/fops.c-531-\t.write_end\t= blkdev_write_end,\nblock/fops.c:532:\t.migrate_folio\t= buffer_migrate_folio_norefs,\nblock/fops.c-533-\t.is_dirty_writeback = buffer_check_dirty_writeback,\n--\nblock/fops.c=585=const struct address_space_operations def_blk_aops = {\n--\nblock/fops.c-593-\t.error_remove_folio\t= generic_error_remove_folio,\nblock/fops.c:594:\t.migrate_folio\t\t= filemap_migrate_folio,\nblock/fops.c-595-};\n--\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c=493=svm_migrate_ram_to_vram(struct svm_range *prange, uint32_t best_loc,\n--\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c-575-\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c:576:static void svm_migrate_folio_free(struct folio *folio)\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c-577-{\n--\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c=1017=static const struct dev_pagemap_ops svm_migrate_pgmap_ops = {\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c:1018:\t.folio_free\t\t= svm_migrate_folio_free,\ndrivers/gpu/drm/amd/amdkfd/kfd_migrate.c-1019-\t.migrate_to_ram\t\t= svm_migrate_to_ram,\n--\ndrivers/gpu/drm/i915/gem/i915_gem_userptr.c=159=i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,\n--\ndrivers/gpu/drm/i915/gem/i915_gem_userptr.c-191-\t\t\t * The mmu-notifier can be invalidated for a\ndrivers/gpu/drm/i915/gem/i915_gem_userptr.c:192:\t\t\t * migrate_folio, that is alreadying holding the lock\ndrivers/gpu/drm/i915/gem/i915_gem_userptr.c-193-\t\t\t * on the folio. Such a try_to_unmap() will result\n--\nfs/9p/vfs_addr.c=160=const struct address_space_operations v9fs_addr_operations = {\n--\nfs/9p/vfs_addr.c-167-\t.writepages\t\t= netfs_writepages,\nfs/9p/vfs_addr.c:168:\t.migrate_folio\t\t= filemap_migrate_folio,\nfs/9p/vfs_addr.c-169-};\n--\nfs/adfs/inode.c=77=static const struct address_space_operations adfs_aops = {\n--\nfs/adfs/inode.c-83-\t.write_end\t= generic_write_end,\nfs/adfs/inode.c:84:\t.migrate_folio\t= buffer_migrate_folio,\nfs/adfs/inode.c-85-\t.bmap\t\t= _adfs_bmap,\n--\nfs/affs/file.c=459=const struct address_space_operations affs_aops = {\n--\nfs/affs/file.c-466-\t.direct_IO = affs_direct_IO,\nfs/affs/file.c:467:\t.migrate_folio = buffer_migrate_folio,\nfs/affs/file.c-468-\t.bmap = _affs_bmap\n--\nfs/affs/file.c=840=const struct address_space_operations affs_aops_ofs = {\n--\nfs/affs/file.c-846-\t.write_end = affs_write_end_ofs,\nfs/affs/file.c:847:\t.migrate_folio = filemap_migrate_folio,\nfs/affs/file.c-848-};\n--\nfs/afs/file.c=52=const struct address_space_operations afs_file_aops = {\n--\nfs/afs/file.c-58-\t.invalidate_folio = netfs_invalidate_folio,\nfs/afs/file.c:59:\t.migrate_folio\t= filemap_migrate_folio,\nfs/afs/file.c-60-\t.writepages\t= afs_writepages,\n--\nfs/aio.c=402=static const struct file_operations aio_ring_fops = {\n--\nfs/aio.c-406-#if IS_ENABLED(CONFIG_MIGRATION)\nfs/aio.c:407:static int aio_migrate_folio(struct address_space *mapping, struct folio *dst,\nfs/aio.c-408-\t\t\tstruct folio *src, enum migrate_mode mode)\n--\nfs/aio.c-473-#else\nfs/aio.c:474:#define aio_migrate_folio NULL\nfs/aio.c-475-#endif\n--\nfs/aio.c=477=static const struct address_space_operations aio_ctx_aops = {\nfs/aio.c-478-\t.dirty_folio\t= noop_dirty_folio,\nfs/aio.c:479:\t.migrate_folio\t= aio_migrate_folio,\nfs/aio.c-480-};\n--\nfs/bfs/file.c=192=const struct address_space_operations bfs_aops = {\n--\nfs/bfs/file.c-198-\t.write_end\t= generic_write_end,\nfs/bfs/file.c:199:\t.migrate_folio\t= buffer_migrate_folio,\nfs/bfs/file.c-200-\t.bmap\t\t= bfs_bmap,\n--\nfs/btrfs/disk-io.c=354=int btrfs_validate_extent_buffer(struct extent_buffer *eb,\n--\nfs/btrfs/disk-io.c-457-#ifdef CONFIG_MIGRATION\nfs/btrfs/disk-io.c:458:static int btree_migrate_folio(struct address_space *mapping,\nfs/btrfs/disk-io.c-459-\t\tstruct folio *dst, struct folio *src, enum migrate_mode mode)\n--\nfs/btrfs/disk-io.c-473-\t\treturn -EAGAIN;\nfs/btrfs/disk-io.c:474:\treturn migrate_folio(mapping, dst, src, mode);\nfs/btrfs/disk-io.c-475-}\nfs/btrfs/disk-io.c-476-#else\nfs/btrfs/disk-io.c:477:#define btree_migrate_folio NULL\nfs/btrfs/disk-io.c-478-#endif\n--\nfs/btrfs/disk-io.c=556=static const struct address_space_operations btree_aops = {\n--\nfs/btrfs/disk-io.c-559-\t.invalidate_folio = btree_invalidate_folio,\nfs/btrfs/disk-io.c:560:\t.migrate_folio\t= btree_migrate_folio,\nfs/btrfs/disk-io.c-561-\t.dirty_folio\t= btree_dirty_folio,\n--\nfs/btrfs/inode.c=7611=static bool btrfs_release_folio(struct folio *folio, gfp_t gfp_flags)\n--\nfs/btrfs/inode.c-7618-#ifdef CONFIG_MIGRATION\nfs/btrfs/inode.c:7619:static int btrfs_migrate_folio(struct address_space *mapping,\nfs/btrfs/inode.c-7620-\t\t\t     struct folio *dst, struct folio *src,\n--\nfs/btrfs/inode.c-7622-{\nfs/btrfs/inode.c:7623:\tint ret = filemap_migrate_folio(mapping, dst, src, mode);\nfs/btrfs/inode.c-7624-\n--\nfs/btrfs/inode.c-7635-#else\nfs/btrfs/inode.c:7636:#define btrfs_migrate_folio NULL\nfs/btrfs/inode.c-7637-#endif\n--\nfs/btrfs/inode.c=10695=static const struct address_space_operations btrfs_aops = {\n--\nfs/btrfs/inode.c-10701-\t.release_folio\t= btrfs_release_folio,\nfs/btrfs/inode.c:10702:\t.migrate_folio\t= btrfs_migrate_folio,\nfs/btrfs/inode.c-10703-\t.dirty_folio\t= filemap_dirty_folio,\n--\nfs/ceph/addr.c=1920=const struct address_space_operations ceph_aops = {\n--\nfs/ceph/addr.c-1929-\t.direct_IO = noop_direct_IO,\nfs/ceph/addr.c:1930:\t.migrate_folio = filemap_migrate_folio,\nfs/ceph/addr.c-1931-};\n--\nfs/ecryptfs/mmap.c=515=const struct address_space_operations ecryptfs_aops = {\n--\nfs/ecryptfs/mmap.c-531-\t.write_end = ecryptfs_write_end,\nfs/ecryptfs/mmap.c:532:\t.migrate_folio = filemap_migrate_folio,\nfs/ecryptfs/mmap.c-533-\t.bmap = ecryptfs_bmap,\n--\nfs/exfat/inode.c=544=static const struct address_space_operations exfat_aops = {\n--\nfs/exfat/inode.c-553-\t.bmap\t\t= exfat_aop_bmap,\nfs/exfat/inode.c:554:\t.migrate_folio\t= buffer_migrate_folio,\nfs/exfat/inode.c-555-};\n--\nfs/ext2/inode.c=971=const struct address_space_operations ext2_aops = {\n--\nfs/ext2/inode.c-979-\t.writepages\t\t= ext2_writepages,\nfs/ext2/inode.c:980:\t.migrate_folio\t\t= buffer_migrate_folio,\nfs/ext2/inode.c-981-\t.is_partially_uptodate\t= block_is_partially_uptodate,\n--\nfs/ext4/inode.c=3924=static const struct address_space_operations ext4_aops = {\n--\nfs/ext4/inode.c-3933-\t.release_folio\t\t= ext4_release_folio,\nfs/ext4/inode.c:3934:\t.migrate_folio\t\t= buffer_migrate_folio,\nfs/ext4/inode.c-3935-\t.is_partially_uptodate  = block_is_partially_uptodate,\n--\nfs/ext4/inode.c=3940=static const struct address_space_operations ext4_journalled_aops = {\n--\nfs/ext4/inode.c-3949-\t.release_folio\t\t= ext4_release_folio,\nfs/ext4/inode.c:3950:\t.migrate_folio\t\t= buffer_migrate_folio_norefs,\nfs/ext4/inode.c-3951-\t.is_partially_uptodate  = block_is_partially_uptodate,\n--\nfs/ext4/inode.c=3956=static const struct address_space_operations ext4_da_aops = {\n--\nfs/ext4/inode.c-3965-\t.release_folio\t\t= ext4_release_folio,\nfs/ext4/inode.c:3966:\t.migrate_folio\t\t= buffer_migrate_folio,\nfs/ext4/inode.c-3967-\t.is_partially_uptodate  = block_is_partially_uptodate,\n--\nfs/f2fs/checkpoint.c=701=const struct address_space_operations f2fs_meta_aops = {\n--\nfs/f2fs/checkpoint.c-705-\t.release_folio\t= f2fs_release_folio,\nfs/f2fs/checkpoint.c:706:\t.migrate_folio\t= filemap_migrate_folio,\nfs/f2fs/checkpoint.c-707-};\n--\nfs/f2fs/compress.c=1909=const struct address_space_operations f2fs_compress_aops = {\n--\nfs/f2fs/compress.c-1911-\t.invalidate_folio = f2fs_invalidate_folio,\nfs/f2fs/compress.c:1912:\t.migrate_folio\t= filemap_migrate_folio,\nfs/f2fs/compress.c-1913-};\n--\nfs/f2fs/data.c=4405=const struct address_space_operations f2fs_dblock_aops = {\n--\nfs/f2fs/data.c-4411-\t.dirty_folio\t= f2fs_dirty_data_folio,\nfs/f2fs/data.c:4412:\t.migrate_folio\t= filemap_migrate_folio,\nfs/f2fs/data.c-4413-\t.invalidate_folio = f2fs_invalidate_folio,\n--\nfs/f2fs/node.c=2308=const struct address_space_operations f2fs_node_aops = {\n--\nfs/f2fs/node.c-2312-\t.release_folio\t= f2fs_release_folio,\nfs/f2fs/node.c:2313:\t.migrate_folio\t= filemap_migrate_folio,\nfs/f2fs/node.c-2314-};\n--\nfs/fat/inode.c=340=static const struct address_space_operations fat_aops = {\n--\nfs/fat/inode.c-349-\t.bmap\t\t= _fat_bmap,\nfs/fat/inode.c:350:\t.migrate_folio\t= buffer_migrate_folio,\nfs/fat/inode.c-351-};\n--\nfs/fuse/file.c=3183=static const struct address_space_operations fuse_file_aops  = {\n--\nfs/fuse/file.c-3191-\t.is_partially_uptodate = iomap_is_partially_uptodate,\nfs/fuse/file.c:3192:\t.migrate_folio\t= filemap_migrate_folio,\nfs/fuse/file.c-3193-\t.bmap\t\t= fuse_bmap,\n--\nfs/gfs2/aops.c=710=static const struct address_space_operations gfs2_aops = {\n--\nfs/gfs2/aops.c-717-\t.bmap = gfs2_bmap,\nfs/gfs2/aops.c:718:\t.migrate_folio = filemap_migrate_folio,\nfs/gfs2/aops.c-719-\t.is_partially_uptodate = iomap_is_partially_uptodate,\n--\nfs/gfs2/aops.c=723=static const struct address_space_operations gfs2_jdata_aops = {\n--\nfs/gfs2/aops.c-728-\t.bmap = gfs2_bmap,\nfs/gfs2/aops.c:729:\t.migrate_folio = buffer_migrate_folio,\nfs/gfs2/aops.c-730-\t.invalidate_folio = gfs2_invalidate_folio,\n--\nfs/gfs2/meta_io.c=101=const struct address_space_operations gfs2_meta_aops = {\n--\nfs/gfs2/meta_io.c-105-\t.release_folio = gfs2_release_folio,\nfs/gfs2/meta_io.c:106:\t.migrate_folio = buffer_migrate_folio_norefs,\nfs/gfs2/meta_io.c-107-};\n--\nfs/gfs2/meta_io.c=109=const struct address_space_operations gfs2_rgrp_aops = {\n--\nfs/gfs2/meta_io.c-113-\t.release_folio = gfs2_release_folio,\nfs/gfs2/meta_io.c:114:\t.migrate_folio = buffer_migrate_folio_norefs,\nfs/gfs2/meta_io.c-115-};\n--\nfs/hfs/inode.c=156=const struct address_space_operations hfs_btree_aops = {\n--\nfs/hfs/inode.c-162-\t.write_end\t= generic_write_end,\nfs/hfs/inode.c:163:\t.migrate_folio\t= buffer_migrate_folio,\nfs/hfs/inode.c-164-\t.bmap\t\t= hfs_bmap,\n--\nfs/hfs/inode.c=168=const struct address_space_operations hfs_aops = {\n--\nfs/hfs/inode.c-176-\t.writepages\t= hfs_writepages,\nfs/hfs/inode.c:177:\t.migrate_folio\t= buffer_migrate_folio,\nfs/hfs/inode.c-178-};\n--\nfs/hfsplus/inode.c=154=const struct address_space_operations hfsplus_btree_aops = {\n--\nfs/hfsplus/inode.c-160-\t.write_end\t= generic_write_end,\nfs/hfsplus/inode.c:161:\t.migrate_folio\t= buffer_migrate_folio,\nfs/hfsplus/inode.c-162-\t.bmap\t\t= hfsplus_bmap,\n--\nfs/hfsplus/inode.c=166=const struct address_space_operations hfsplus_aops = {\n--\nfs/hfsplus/inode.c-174-\t.writepages\t= hfsplus_writepages,\nfs/hfsplus/inode.c:175:\t.migrate_folio\t= buffer_migrate_folio,\nfs/hfsplus/inode.c-176-};\n--\nfs/hostfs/hostfs_kern.c=491=static const struct address_space_operations hostfs_aops = {\n--\nfs/hostfs/hostfs_kern.c-496-\t.write_end\t= hostfs_write_end,\nfs/hostfs/hostfs_kern.c:497:\t.migrate_folio\t= filemap_migrate_folio,\nfs/hostfs/hostfs_kern.c-498-};\n--\nfs/hpfs/file.c=245=const struct address_space_operations hpfs_aops = {\n--\nfs/hpfs/file.c-253-\t.bmap = _hpfs_bmap,\nfs/hpfs/file.c:254:\t.migrate_folio = buffer_migrate_folio,\nfs/hpfs/file.c-255-};\n--\nfs/hugetlbfs/inode.c=1032=static int hugetlbfs_symlink(struct mnt_idmap *idmap,\n--\nfs/hugetlbfs/inode.c-1054-#ifdef CONFIG_MIGRATION\nfs/hugetlbfs/inode.c:1055:static int hugetlbfs_migrate_folio(struct address_space *mapping,\nfs/hugetlbfs/inode.c-1056-\t\t\t\tstruct folio *dst, struct folio *src,\n--\nfs/hugetlbfs/inode.c-1075-#else\nfs/hugetlbfs/inode.c:1076:#define hugetlbfs_migrate_folio NULL\nfs/hugetlbfs/inode.c-1077-#endif\n--\nfs/hugetlbfs/inode.c=1223=static const struct address_space_operations hugetlbfs_aops = {\n--\nfs/hugetlbfs/inode.c-1226-\t.dirty_folio\t= noop_dirty_folio,\nfs/hugetlbfs/inode.c:1227:\t.migrate_folio  = hugetlbfs_migrate_folio,\nfs/hugetlbfs/inode.c-1228-\t.error_remove_folio\t= hugetlbfs_error_remove_folio,\n--\nfs/jfs/inode.c=356=const struct address_space_operations jfs_aops = {\n--\nfs/jfs/inode.c-365-\t.direct_IO\t= jfs_direct_IO,\nfs/jfs/inode.c:366:\t.migrate_folio\t= buffer_migrate_folio,\nfs/jfs/inode.c-367-};\n--\nfs/jfs/jfs_metapage.c=143=static inline void dec_io(struct folio *folio, blk_status_t status,\n--\nfs/jfs/jfs_metapage.c-155-#ifdef CONFIG_MIGRATION\nfs/jfs/jfs_metapage.c:156:static int __metapage_migrate_folio(struct address_space *mapping,\nfs/jfs/jfs_metapage.c-157-\t\t\t\t    struct folio *dst, struct folio *src,\n--\nfs/jfs/jfs_metapage.c-170-\nfs/jfs/jfs_metapage.c:171:\trc = filemap_migrate_folio(mapping, dst, src, mode);\nfs/jfs/jfs_metapage.c-172-\tif (rc)\n--\nfs/jfs/jfs_metapage.c=222=static inline void remove_metapage(struct folio *folio, struct metapage *mp)\n--\nfs/jfs/jfs_metapage.c-231-#ifdef CONFIG_MIGRATION\nfs/jfs/jfs_metapage.c:232:static int __metapage_migrate_folio(struct address_space *mapping,\nfs/jfs/jfs_metapage.c-233-\t\t\t\t    struct folio *dst, struct folio *src,\n--\nfs/jfs/jfs_metapage.c-243-\nfs/jfs/jfs_metapage.c:244:\trc = filemap_migrate_folio(mapping, dst, src, mode);\nfs/jfs/jfs_metapage.c-245-\tif (rc)\n--\nfs/jfs/jfs_metapage.c=612=static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)\n--\nfs/jfs/jfs_metapage.c-642-/*\nfs/jfs/jfs_metapage.c:643: * metapage_migrate_folio - Migration function for JFS metapages\nfs/jfs/jfs_metapage.c-644- */\nfs/jfs/jfs_metapage.c:645:static int metapage_migrate_folio(struct address_space *mapping,\nfs/jfs/jfs_metapage.c-646-\t\t\t\t  struct folio *dst, struct folio *src,\n--\nfs/jfs/jfs_metapage.c-651-\tif (!src-\u003eprivate)\nfs/jfs/jfs_metapage.c:652:\t\treturn filemap_migrate_folio(mapping, dst, src, mode);\nfs/jfs/jfs_metapage.c-653-\n--\nfs/jfs/jfs_metapage.c-657-\t\treturn -EAGAIN;\nfs/jfs/jfs_metapage.c:658:\treturn __metapage_migrate_folio(mapping, dst, src, mode);\nfs/jfs/jfs_metapage.c-659-}\nfs/jfs/jfs_metapage.c-660-#else\nfs/jfs/jfs_metapage.c:661:#define metapage_migrate_folio NULL\nfs/jfs/jfs_metapage.c-662-#endif\t/* CONFIG_MIGRATION */\n--\nfs/jfs/jfs_metapage.c=674=const struct address_space_operations jfs_metapage_aops = {\n--\nfs/jfs/jfs_metapage.c-679-\t.dirty_folio\t= filemap_dirty_folio,\nfs/jfs/jfs_metapage.c:680:\t.migrate_folio\t= metapage_migrate_folio,\nfs/jfs/jfs_metapage.c-681-};\n--\nfs/minix/inode.c=488=static const struct address_space_operations minix_aops = {\n--\nfs/minix/inode.c-494-\t.write_end = generic_write_end,\nfs/minix/inode.c:495:\t.migrate_folio = buffer_migrate_folio,\nfs/minix/inode.c-496-\t.bmap = minix_bmap,\n--\nfs/nfs/file.c=618=const struct address_space_operations nfs_file_aops = {\n--\nfs/nfs/file.c-626-\t.release_folio = nfs_release_folio,\nfs/nfs/file.c:627:\t.migrate_folio = nfs_migrate_folio,\nfs/nfs/file.c-628-\t.launder_folio = nfs_launder_folio,\n--\nfs/nfs/internal.h=661=void nfs_clear_pnfs_ds_commit_verifiers(struct pnfs_ds_commit_info *cinfo)\n--\nfs/nfs/internal.h-666-#ifdef CONFIG_MIGRATION\nfs/nfs/internal.h:667:int nfs_migrate_folio(struct address_space *, struct folio *dst,\nfs/nfs/internal.h-668-\t\tstruct folio *src, enum migrate_mode);\nfs/nfs/internal.h-669-#else\nfs/nfs/internal.h:670:#define nfs_migrate_folio NULL\nfs/nfs/internal.h-671-#endif\n--\nfs/nfs/write.c=2068=int nfs_wb_folio(struct inode *inode, struct folio *folio)\n--\nfs/nfs/write.c-2102-#ifdef CONFIG_MIGRATION\nfs/nfs/write.c:2103:int nfs_migrate_folio(struct address_space *mapping, struct folio *dst,\nfs/nfs/write.c-2104-\t\tstruct folio *src, enum migrate_mode mode)\n--\nfs/nfs/write.c-2126-\nfs/nfs/write.c:2127:\treturn migrate_folio(mapping, dst, src, mode);\nfs/nfs/write.c-2128-}\n--\nfs/nilfs2/inode.c=272=const struct address_space_operations nilfs_aops = {\n--\nfs/nilfs2/inode.c-280-\t.direct_IO\t\t= nilfs_direct_IO,\nfs/nilfs2/inode.c:281:\t.migrate_folio\t\t= buffer_migrate_folio_norefs,\nfs/nilfs2/inode.c-282-\t.is_partially_uptodate  = block_is_partially_uptodate,\n--\nfs/nilfs2/mdt.c=441=static const struct address_space_operations def_mdt_aops = {\n--\nfs/nilfs2/mdt.c-444-\t.writepages\t\t= nilfs_mdt_writeback,\nfs/nilfs2/mdt.c:445:\t.migrate_folio\t\t= buffer_migrate_folio_norefs,\nfs/nilfs2/mdt.c-446-};\n--\nfs/ntfs3/inode.c=2149=const struct address_space_operations ntfs_aops = {\n--\nfs/ntfs3/inode.c-2154-\t.dirty_folio\t= iomap_dirty_folio,\nfs/ntfs3/inode.c:2155:\t.migrate_folio\t= filemap_migrate_folio,\nfs/ntfs3/inode.c-2156-\t.release_folio\t= iomap_release_folio,\n--\nfs/ocfs2/aops.c=2445=const struct address_space_operations ocfs2_aops = {\n--\nfs/ocfs2/aops.c-2455-\t.release_folio\t\t= ocfs2_release_folio,\nfs/ocfs2/aops.c:2456:\t.migrate_folio\t\t= buffer_migrate_folio,\nfs/ocfs2/aops.c-2457-\t.is_partially_uptodate\t= block_is_partially_uptodate,\n--\nfs/omfs/file.c=369=const struct address_space_operations omfs_aops = {\n--\nfs/omfs/file.c-377-\t.bmap = omfs_bmap,\nfs/omfs/file.c:378:\t.migrate_folio = buffer_migrate_folio,\nfs/omfs/file.c-379-};\n--\nfs/orangefs/inode.c=590=static const struct address_space_operations orangefs_address_operations = {\n--\nfs/orangefs/inode.c-599-\t.free_folio = orangefs_free_folio,\nfs/orangefs/inode.c:600:\t.migrate_folio = filemap_migrate_folio,\nfs/orangefs/inode.c-601-\t.launder_folio = orangefs_launder_folio,\n--\nfs/smb/client/file.c=3328=const struct address_space_operations cifs_addr_ops = {\n--\nfs/smb/client/file.c-3335-\t.invalidate_folio = netfs_invalidate_folio,\nfs/smb/client/file.c:3336:\t.migrate_folio\t= filemap_migrate_folio,\nfs/smb/client/file.c-3337-\t/*\n--\nfs/smb/client/file.c=3351=const struct address_space_operations cifs_addr_ops_smallbuf = {\n--\nfs/smb/client/file.c-3356-\t.invalidate_folio = netfs_invalidate_folio,\nfs/smb/client/file.c:3357:\t.migrate_folio\t= filemap_migrate_folio,\nfs/smb/client/file.c-3358-};\n--\nfs/ubifs/file.c=1625=const struct address_space_operations ubifs_file_address_operations = {\n--\nfs/ubifs/file.c-1631-\t.dirty_folio\t= ubifs_dirty_folio,\nfs/ubifs/file.c:1632:\t.migrate_folio\t= filemap_migrate_folio,\nfs/ubifs/file.c-1633-\t.release_folio\t= ubifs_release_folio,\n--\nfs/udf/inode.c=327=const struct address_space_operations udf_aops = {\n--\nfs/udf/inode.c-336-\t.bmap\t\t= udf_bmap,\nfs/udf/inode.c:337:\t.migrate_folio\t= buffer_migrate_folio,\nfs/udf/inode.c-338-};\n--\nfs/ufs/inode.c=509=const struct address_space_operations ufs_aops = {\n--\nfs/ufs/inode.c-515-\t.write_end = ufs_write_end,\nfs/ufs/inode.c:516:\t.migrate_folio = buffer_migrate_folio,\nfs/ufs/inode.c-517-\t.bmap = ufs_bmap\n--\nfs/vboxsf/file.c=350=const struct address_space_operations vboxsf_reg_aops = {\n--\nfs/vboxsf/file.c-355-\t.write_end = vboxsf_write_end,\nfs/vboxsf/file.c:356:\t.migrate_folio = filemap_migrate_folio,\nfs/vboxsf/file.c-357-};\n--\nfs/xfs/xfs_aops.c=806=const struct address_space_operations xfs_address_space_operations = {\n--\nfs/xfs/xfs_aops.c-813-\t.bmap\t\t\t= xfs_vm_bmap,\nfs/xfs/xfs_aops.c:814:\t.migrate_folio\t\t= filemap_migrate_folio,\nfs/xfs/xfs_aops.c-815-\t.is_partially_uptodate  = iomap_is_partially_uptodate,\n--\nfs/zonefs/file.c=185=const struct address_space_operations zonefs_file_aops = {\n--\nfs/zonefs/file.c-191-\t.invalidate_folio\t= iomap_invalidate_folio,\nfs/zonefs/file.c:192:\t.migrate_folio\t\t= filemap_migrate_folio,\nfs/zonefs/file.c-193-\t.is_partially_uptodate\t= iomap_is_partially_uptodate,\n--\ninclude/linux/buffer_head.h=278=int block_truncate_page(struct address_space *, loff_t, get_block_t *);\n--\ninclude/linux/buffer_head.h-280-#ifdef CONFIG_MIGRATION\ninclude/linux/buffer_head.h:281:extern int buffer_migrate_folio(struct address_space *,\ninclude/linux/buffer_head.h-282-\t\tstruct folio *dst, struct folio *src, enum migrate_mode);\ninclude/linux/buffer_head.h:283:extern int buffer_migrate_folio_norefs(struct address_space *,\ninclude/linux/buffer_head.h-284-\t\tstruct folio *dst, struct folio *src, enum migrate_mode);\ninclude/linux/buffer_head.h-285-#else\ninclude/linux/buffer_head.h:286:#define buffer_migrate_folio NULL\ninclude/linux/buffer_head.h:287:#define buffer_migrate_folio_norefs NULL\ninclude/linux/buffer_head.h-288-#endif\n--\ninclude/linux/fs.h=403=struct address_space_operations {\n--\ninclude/linux/fs.h-430-\t */\ninclude/linux/fs.h:431:\tint (*migrate_folio)(struct address_space *, struct folio *dst,\ninclude/linux/fs.h-432-\t\t\tstruct folio *src, enum migrate_mode);\n--\ninclude/linux/migrate.h=56=void putback_movable_pages(struct list_head *l);\ninclude/linux/migrate.h:57:int migrate_folio(struct address_space *mapping, struct folio *dst,\ninclude/linux/migrate.h-58-\t\tstruct folio *src, enum migrate_mode mode);\n--\ninclude/linux/pagemap.h=1276=bool noop_dirty_folio(struct address_space *mapping, struct folio *folio);\n--\ninclude/linux/pagemap.h-1278-#ifdef CONFIG_MIGRATION\ninclude/linux/pagemap.h:1279:int filemap_migrate_folio(struct address_space *mapping, struct folio *dst,\ninclude/linux/pagemap.h-1280-\t\tstruct folio *src, enum migrate_mode mode);\ninclude/linux/pagemap.h-1281-#else\ninclude/linux/pagemap.h:1282:#define filemap_migrate_folio NULL\ninclude/linux/pagemap.h-1283-#endif\n--\nmm/compaction.c=837=isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,\n--\nmm/compaction.c-1121-\t\t\t * Only folios without mappings or that have\nmm/compaction.c:1122:\t\t\t * a -\u003emigrate_folio callback are possible to migrate\nmm/compaction.c-1123-\t\t\t * without blocking.\n--\nmm/compaction.c-1143-\t\t\t\tmigrate_dirty = !mapping ||\n\n"
}

gemini-3.1-pro-preview

null

null

							input: 44455
							output: 20
							thoughts: 927
						

**Analyzing the Async Folio Migration Path**

Okay, let's break this down. My initial observation is that `migrate_folio` is a key function called from several places: `btrfs`, `nfs`, and the core memory management code via `__migrate_folio`. It appears `__migrate_folio` is the entry point that employs `MIGRATE_ASYNC_NON_TEMPORAL_STORES`, which is interesting. This flag propagates down through a call chain I’ve traced: `migrate_pages_batch` -> `migrate_folio_unmap` -> `__migrate_folio`. Essentially, `MIGRATE_ASYNC_NON_TEMPORAL_STORES` is passed to filesystems, via the filesystem's `migrate_folio` function.

Now, the patch modifies `nfs_migrate_folio` to check if `migrate_mode_is_async(mode)` instead of `mode == MIGRATE_ASYNC`, which suggests that `MIGRATE_ASYNC_NON_TEMPORAL_STORES` is effectively treated as `MIGRATE_ASYNC`. This is crucial. I need to understand where `MIGRATE_ASYNC_NON_TEMPORAL_STORES` actually gets set. Tracing back, it seems to be solely generated within `migrate_pages` when the `reason` is `MR_DEMOTION` and the `mode` is `MIGRATE_ASYNC`.

`MR_DEMOTION` is exclusively used within `demote_folio_list`. This implies this "async non-temporal store" behavior is only triggered during memory demotion. Demotion requires `numa_demotion_enabled` to be true. So the feature depends on memory demotion being enabled.

Let's see if we can trigger this path with Syzkaller. It appears it can manipulate `/sys/kernel/mm/numa/demotion_enabled` to enable it, triggering page reclaim (e.g., allocating lots of memory) in the process. This likely invokes `shrink_folio_list` -> `demote_folio_list` -> `migrate_pages` with `MR_DEMOTION`, thus firing up the new logic introduced by the patch in `migrate_pages` and `copy_mc_to_kernel_nt`.

Consequently, this path is indeed reachable and functional, assuming the correct configurations are in place. The necessary configurations are: `CONFIG_NUMA`, `CONFIG_MIGRATION`, and `CONFIG_X86_64` (for `copy_mc_to_kernel_nt` and `ARCH_HAS_UACCESS_FLUSHCACHE`, that is because `copy_mc_to_kernel_nt` is defined in `arch/x86/lib/copy_mc.c`, which is compiled if `CONFIG_ARCH_HAS_COPY_MC` is set, and this is selected by `X86_64`). And it appears `CONFIG_MEMORY_TIERING` is unrelated.

no matches

{
  "Expression": "config MEMORY_TIERING"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 46064
							output: 30
							thoughts: 40
						

Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of kernel configuration:

**Kernel Configuration Hunting**

Alright, hang on a second. I swear I searched for `config MEMORY_TIERING` not too long ago and came up completely dry. That's odd. It's got to be in there *somewhere*. Time to go back to basics, though. If memory tiering isn't a direct config symbol, it's likely related to NUMA or some broader memory management feature. So, let me just quickly glance through `mm/Kconfig`. That's the likely spot for anything related to memory management, NUMA concepts, or tiering approaches. I'll search that file for keywords. It is a good place to start.

no matches

{
  "Expression": "NUMA_BALANCING",
  "PathPrefix": "mm/Kconfig"
}

{
  "error": "no matches"
}

gemini-3.1-pro-preview

null

null

							input: 46316
							output: 21
							thoughts: 24
						

Okay, here's my interpretation of that thought process, from an expert's perspective:

**Finding the NUMA_BALANCING Configuration**

Right, so I need to track down the configuration option for `NUMA_BALANCING`. The most logical place to start, given my experience, is within the kernel's Kconfig system. Specifically, I'm thinking I'll find it either directly in the top-level `Kconfig` file, or perhaps nested deeper within the `init/` subdirectory's `Kconfig`. That's where a lot of the initial setup and core system configurations reside, so it's a good bet. My initial instinct is to check `init/Kconfig` first, given it seems the most appropriate place, but if I don't find it there, then I will immediately search the top-level `Kconfig` next. This seems a pretty straight-forward search, so I don't anticipate any issues!

{
  "Expression": "config NUMA_BALANCING"
}

{
  "Output": "init/Kconfig=993=config ARCH_WANT_NUMA_VARIABLE_LOCALITY\n--\ninit/Kconfig-995-\ninit/Kconfig:996:config NUMA_BALANCING\ninit/Kconfig-997-\tbool \"Memory placement aware NUMA scheduler\"\n--\ninit/Kconfig-1007-\ninit/Kconfig:1008:config NUMA_BALANCING_DEFAULT_ENABLED\ninit/Kconfig-1009-\tbool \"Automatically enable NUMA aware memory/task placement\"\n"
}

gemini-3.1-pro-preview

null

null

							input: 46708
							output: 33
							thoughts: 38
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Memory Demotion and NUMA Balancing: A Quick Check**

Okay, so I'm thinking about memory demotion, and the question that pops into my head is whether `NUMA_BALANCING` has a direct influence on its operation. It's a key question, as balancing decisions directly impact where pages ultimately reside. Therefore, I need to know if the two are intrinsically linked in any way.

My immediate instinct is to dive into the core VM code. I'm going to head straight for `mm/vmscan.c`. It's where the heart of page scanning and reclaim logic lives, and where I expect to find the definition of `numa_demotion_enabled`. A quick grep there should give me a definitive answer to see how memory demotion is implemented in relation to NUMA-specific features, and whether `NUMA_BALANCING` actively triggers or interacts with the memory demotion process. From there, I can analyze the callsites and determine the level of integration or independence between the two. This is going to be a quick but thorough way to understand the control flow, the dependencies, and the assumptions at play.

{
  "Expression": "numa_demotion_enabled",
  "PathPrefix": "mm/vmscan.c"
}

{
  "Output": "mm/vmscan.c=343=static bool can_demote(int nid, struct scan_control *sc,\n--\nmm/vmscan.c-348-\nmm/vmscan.c:349:\tif (!pgdat || !numa_demotion_enabled)\nmm/vmscan.c-350-\t\treturn false;\n"
}

gemini-3.1-pro-preview

null

null

							input: 47136
							output: 40
							thoughts: 570
						

**Analyzing NUMA Demotion and Migration Code**

Okay, so I'm digging into this code and the first thing that jumps out is the dependency of `can_demote`. It's not checking `NUMA_BALANCING`, which is interesting. It's only looking at `numa_demotion_enabled`, and that's defined in `mm/memory-tiers.c`. That file, `mm/memory-tiers.c`, gets compiled only if `CONFIG_NUMA` is set.  So, besides `CONFIG_X86_64`, it seems like `CONFIG_NUMA` and `CONFIG_MIGRATION` are the only *required* configs. Good to keep in mind as I assess the broader implications.

Now, I'm thinking about the key symbols to focus on here to get a handle on what's going on. I've initially jotted down `copy_mc_to_kernel_nt`, `folio_mc_copy_nt`, `demote_folio_list`, `migrate_pages`, and `__migrate_folio`... let me double-check where they are defined.

Okay, so `copy_mc_to_kernel_nt` is in `arch/x86/lib/copy_mc.c`. `folio_mc_copy_nt` is in `mm/util.c`. `demote_folio_list` is static to `mm/vmscan.c`. `migrate_pages` is in `mm/migrate.c`, and `__migrate_folio` is also static within `mm/migrate.c`. Good to know where they are.

Next, I need to check if they're exported symbols. Ah, yes, `copy_mc_to_kernel_nt` is exported with `EXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt)`, and `folio_mc_copy_nt` is exported with `EXPORT_SYMBOL(folio_mc_copy_nt)`.

So, the focus symbols I need to keep in mind are, therefore: `copy_mc_to_kernel_nt`, `folio_mc_copy_nt`, and `migrate_pages`.

I'm also curious about `MIGRATE_ASYNC_NON_TEMPORAL_STORES`... let me quickly check where else it is used. Okay, it looks like it is used indirectly via `migrate_mode_is_async` in `nfs_migrate_folio`. It's also used the same way in `mm/compaction.c` and in `mm/migrate.c`.

Okay, back to the focus. I'm noting that `migrate_pages` is likely a frequently called function if migration is happening. But, `folio_mc_copy_nt` and `copy_mc_to_kernel_nt` seem to be directly related to this patch and this memory copy process.  So, these are good candidates for closer inspection.

Let me now delve into `copy_mc_to_kernel_nt` within `arch/x86/lib/copy_mc.c` and see what it's doing.

{
  "File": "arch/x86/lib/copy_mc.c",
  "FirstLine": 80,
  "LineCount": 30
}

{
  "Contents": "  80:\t\treturn 0;\n  81:\t}\n  82:\tEXPORT_SYMBOL_GPL(copy_mc_to_kernel);\n  83:\t\n  84:\t/**\n  85:\t * copy_mc_to_kernel_nt - memory copy that handles source exceptions\n  86:\t * if enabled, otherwise uses non-temporal stores\n  87:\t * @dst: destination address\n  88:\t * @src: source address\n  89:\t * @len: number of bytes to copy\n  90:\t *\n  91:\t * Return 0 for success, or number of bytes not copied if there was an\n  92:\t * exception.\n  93:\t */\n  94:\tunsigned long __must_check copy_mc_to_kernel_nt(void *dst, const void *src, unsigned len)\n  95:\t{\n  96:\t\tunsigned long ret;\n  97:\t\n  98:\t\tif (copy_mc_fragile_enabled) {\n  99:\t\t\tinstrument_memcpy_before(dst, src, len);\n 100:\t\t\tret = copy_mc_fragile(dst, src, len);\n 101:\t\t\tinstrument_memcpy_after(dst, src, len, ret);\n 102:\t\t\treturn ret;\n 103:\t\t}\n 104:\t\n 105:\t\tmemcpy_flushcache(dst, src, len);\n 106:\t\treturn 0;\n 107:\t}\n 108:\tEXPORT_SYMBOL_GPL(copy_mc_to_kernel_nt);\n 109:\t\n"
}

gemini-3.1-pro-preview

null

null

							input: 48843
							output: 33
							thoughts: 41
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, and presented as a first-person summary:

**Focusing on the Memory Copy Operation**

Yes, `copy_mc_to_kernel_nt` – that's a solid symbol to hone in on. A good starting point. My thinking is, let's trace this function and see where it goes.

Next up, I should take a look at `folio_mc_copy_nt`, found in `mm/util.c`. This will allow me to track the memory copy operations. I want to understand exactly how the non-temporal copy works, how it's integrated, and any potential areas for optimization or bottlenecks within that function. I'll need to check the interactions with the folio structures and the underlying memory management mechanisms. I need to understand all the mechanics of how the copy function and its parameters work together.

{
  "File": "mm/util.c",
  "FirstLine": 745,
  "LineCount": 30
}

{
  "Contents": " 745:\t\t\tcond_resched();\n 746:\t\t}\n 747:\t\n 748:\t\treturn 0;\n 749:\t}\n 750:\tEXPORT_SYMBOL(folio_mc_copy);\n 751:\t\n 752:\tint folio_mc_copy_nt(struct folio *dst, struct folio *src)\n 753:\t{\n 754:\t\tlong nr = folio_nr_pages(src);\n 755:\t\tlong i = 0;\n 756:\t\n 757:\t\tfor (;;) {\n 758:\t\t\tif (copy_mc_highpage_nt(folio_page(dst, i), folio_page(src, i)))\n 759:\t\t\t\treturn -EHWPOISON;\n 760:\t\t\tif (++i == nr)\n 761:\t\t\t\tbreak;\n 762:\t\t\tcond_resched();\n 763:\t\t}\n 764:\t\n 765:\t\treturn 0;\n 766:\t}\n 767:\tEXPORT_SYMBOL(folio_mc_copy_nt);\n 768:\t\n 769:\tint sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;\n 770:\tstatic int sysctl_overcommit_ratio __read_mostly = 50;\n 771:\tstatic unsigned long sysctl_overcommit_kbytes __read_mostly;\n 772:\tint sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;\n 773:\tunsigned long sysctl_user_reserve_kbytes __read_mostly = 1UL \u003c\u003c 17; /* 128MB */\n 774:\tunsigned long sysctl_admin_reserve_kbytes __read_mostly = 1UL \u003c\u003c 13; /* 8MB */\n"
}

gemini-3.1-pro-preview

null

null

							input: 49593
							output: 33
							thoughts: 36
						

Okay, here's my interpretation of those thoughts, tailored for an expert audience, and delivered as a first-person summary:

**Focusing on Migration Implementation Details**

Right, `folio_mc_copy_nt` feels like a solid choice for the focus symbol in this context. It's the right level of abstraction for what I'm looking at. Now, let's dive into the core migration implementation. I'm going to check `__migrate_folio` within `mm/migrate.c`. I need to understand exactly how the folio migration process works, and what `__migrate_folio` is doing at the low level. My immediate objective is to understand how this function utilizes that specific focus symbol. This will likely give me key insights into understanding the migration process.

{
  "File": "mm/migrate.c",
  "FirstLine": 850,
  "LineCount": 30
}

{
  "Contents": " 850:\t\n 851:\t/************************************************************\n 852:\t *                    Migration functions\n 853:\t ***********************************************************/\n 854:\t\n 855:\tstatic int __migrate_folio(struct address_space *mapping, struct folio *dst,\n 856:\t\t\t\t   struct folio *src, void *src_private,\n 857:\t\t\t\t   enum migrate_mode mode)\n 858:\t{\n 859:\t\tint rc, expected_count = folio_expected_ref_count(src) + 1;\n 860:\t\n 861:\t\t/* Check whether src does not have extra refs before we do more work */\n 862:\t\tif (folio_ref_count(src) != expected_count)\n 863:\t\t\treturn -EAGAIN;\n 864:\t\n 865:\t\tif (mode == MIGRATE_ASYNC_NON_TEMPORAL_STORES)\n 866:\t\t\trc = folio_mc_copy_nt(dst, src);\n 867:\t\telse\n 868:\t\t\trc = folio_mc_copy(dst, src);\n 869:\t\tif (unlikely(rc))\n 870:\t\t\treturn rc;\n 871:\t\n 872:\t\trc = __folio_migrate_mapping(mapping, dst, src, expected_count);\n 873:\t\tif (rc)\n 874:\t\t\treturn rc;\n 875:\t\n 876:\t\tif (src_private)\n 877:\t\t\tfolio_attach_private(dst, folio_detach_private(src));\n 878:\t\n 879:\t\tfolio_migrate_flags(dst, src);\n"
}

gemini-3.1-pro-preview

null

null

							input: 50274
							output: 34
							thoughts: 37
						

Okay, let's see...

**Analyzing Potential Focus Symbols**

Hmm, so `__migrate_folio` is declared as static. That's not ideal for a focus symbol, I need something that's potentially more accessible. It's a key function in folio migration, so it's worth further inspection to determine what's happening.

Let's switch gears and go look at `migrate_pages` function in `mm/migrate.c`. Hopefully, this will lead me to the right location.

{
  "File": "mm/migrate.c",
  "FirstLine": 2070,
  "LineCount": 30
}

{
  "Contents": "2070:\t * Returns the number of {normal folio, large folio, hugetlb} that were not\n2071:\t * migrated, or an error code. The number of large folio splits will be\n2072:\t * considered as the number of non-migrated large folio, no matter how many\n2073:\t * split folios of the large folio are migrated successfully.\n2074:\t */\n2075:\tint migrate_pages(struct list_head *from, new_folio_t get_new_folio,\n2076:\t\t\tfree_folio_t put_new_folio, unsigned long private,\n2077:\t\t\tenum migrate_mode mode, int reason, unsigned int *ret_succeeded)\n2078:\t{\n2079:\t\tint rc, rc_gather;\n2080:\t\tint nr_pages;\n2081:\t\tstruct folio *folio, *folio2;\n2082:\t\tLIST_HEAD(folios);\n2083:\t\tLIST_HEAD(ret_folios);\n2084:\t\tLIST_HEAD(split_folios);\n2085:\t\tstruct migrate_pages_stats stats;\n2086:\t\n2087:\t\tif (IS_ENABLED(CONFIG_X86_64) \u0026\u0026\n2088:\t\t\tIS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) \u0026\u0026\n2089:\t\t\treason == MR_DEMOTION \u0026\u0026 mode == MIGRATE_ASYNC)\n2090:\t\t\tmode = MIGRATE_ASYNC_NON_TEMPORAL_STORES;\n2091:\t\n2092:\t\ttrace_mm_migrate_pages_start(mode, reason);\n2093:\t\n2094:\t\tmemset(\u0026stats, 0, sizeof(stats));\n2095:\t\n2096:\t\trc_gather = migrate_hugetlbs(from, get_new_folio, put_new_folio, private,\n2097:\t\t\t\t\t     mode, reason, \u0026stats, \u0026ret_folios);\n2098:\t\tif (rc_gather \u003c 0)\n2099:\t\t\tgoto out;\n"
}

gemini-3.1-pro-preview

null

null

							input: 50992
							output: 36
							thoughts: 517
						

**Focusing the Fuzzer for Effective Testing**

Okay, so I'm thinking about how best to guide the fuzzer to the new memory migration code. Initially, I considered `migrate_pages` as a good focus symbol, since it's exported and seems central to the overall page migration process. However, that function is incredibly common and likely used in a wide variety of migration scenarios, including compaction and NUMA balancing. This could result in a lot of irrelevant noise and make it harder to pinpoint issues within the specific code I'm targeting.

Then I realized that `folio_mc_copy_nt` and `copy_mc_to_kernel_nt` are much more specific and directly related to the new functionality. Focusing on these two functions seems like the best approach to ensure the fuzzer spends its time exploring the new migration paths. These seem to be the most promising focus symbols.

Now, let's explore if there are any other useful exported functions or configuration options we should consider. I also need to make sure I haven't missed any edge cases. I've found `migrate_mode_is_async`, but it's an inline function, so it's not directly exported. Similarly, `copy_mc_highpage_nt` is also inline, though it's still worth noting.

So, the focus symbols remain:

*   `copy_mc_to_kernel_nt`
*   `folio_mc_copy_nt`

Regarding config options, I originally thought about including `X86_64` because the code is specific to that architecture. But then I remembered that Syzkaller usually runs on x86_64 by default, so we probably don't need to specify that explicitly. Instead, I think `NUMA` and `MIGRATION` are more important.

Wait, `CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE` is selected by `X86_64`. So even if `X86_64` is implicit, including `NUMA` and `MIGRATION` ensures that configuration details are not accidentally omitted.

Let me just double-check the dependencies for `MIGRATION`. It depends on `NUMA` or `COMPACTION`. Since `NUMA` is often enabled in Syzkaller configs, that looks solid. So `NUMA` and `MIGRATION` it is.

One last thing, let's look at `CONFIG_MEMORY_FAILURE` because the patch mentions `memory_failure_queue` in `copy_mc_highpage_nt`. I'll cross-reference the `include/linux/highmem.h` file to confirm.

{
  "File": "include/linux/highmem.h",
  "FirstLine": 465,
  "LineCount": 30
}

{
  "Contents": " 465:\t\n 466:\t\tif (ret)\n 467:\t\t\tmemory_failure_queue(page_to_pfn(from), 0);\n 468:\t\n 469:\t\treturn ret;\n 470:\t}\n 471:\t\n 472:\t#ifdef copy_mc_to_kernel_nt\n 473:\tstatic inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n 474:\t{\n 475:\t\tunsigned long ret;\n 476:\t\tchar *vfrom, *vto;\n 477:\t\n 478:\t\tvfrom = kmap_local_page(from);\n 479:\t\tvto = kmap_local_page(to);\n 480:\t\tret = copy_mc_to_kernel_nt(vto, vfrom, PAGE_SIZE);\n 481:\t\tif (!ret)\n 482:\t\t\tkmsan_copy_page_meta(to, from);\n 483:\t\tkunmap_local(vto);\n 484:\t\tkunmap_local(vfrom);\n 485:\t\n 486:\t\tif (ret)\n 487:\t\t\tmemory_failure_queue(page_to_pfn(from), 0);\n 488:\t\n 489:\t\treturn ret;\n 490:\t}\n 491:\t#else\n 492:\tstatic inline int copy_mc_highpage_nt(struct page *to, struct page *from)\n 493:\t{\n 494:\t\treturn copy_mc_highpage(to, from);\n"
}

gemini-3.1-pro-preview

null

null

							input: 52554
							output: 19
							thoughts: 43
						

**Analyzing the Memory Failure Handling**

Okay, so I see a call to `memory_failure_queue` triggered when `ret` isn't zero. That immediately flags something to me. The code's designed to manage memory errors, likely a critical part of ensuring stability. Now, my mind immediately jumps to `MEMORY_FAILURE`. I need to figure out the context of this configuration. Is `MEMORY_FAILURE` even something that's actively utilized, or is it legacy code? The efficiency of the software depends on minimizing unnecessary checks or operations, so I'll need to dig deeper. I'll check its definition and references to see whether it is relevant to the execution path currently being inspected.

{
  "Expression": "config MEMORY_FAILURE"
}

{
  "Output": "mm/Kconfig=722=config ARCH_SUPPORTS_MEMORY_FAILURE\n--\nmm/Kconfig-724-\nmm/Kconfig:725:config MEMORY_FAILURE\nmm/Kconfig-726-\tdepends on MMU\n"
}

gemini-3.1-pro-preview

null

null

							input: 52835
							output: 176
							thoughts: 324
						

**My Fuzzing Strategy for Non-Temporal Memory Copy**

Okay, so I'm thinking about how to effectively fuzz this new non-temporal memory copy functionality. While compiling and testing the core memory copy routine itself isn't strictly *essential* at this point (though machine check handling is tangentially relevant), the primary focus here is really on the non-temporal aspect used during memory demotion. So, `NUMA` and `MIGRATION` are key enabling configurations.

Let's break it down:

*   **`WorthFuzzing: true`**: Definitely. This is a new code path worth exploring for potential vulnerabilities.
*   **`FocusSymbols: copy_mc_to_kernel_nt`, `folio_mc_copy_nt`**: These are the functions that implement the non-temporal copy specifically. These are the prime targets for fuzzing.
*   **`EnableConfigs: NUMA`, `MIGRATION`**: These are crucial because the new `MIGRATE_ASYNC_NON_TEMPORAL_STORES` mode is triggered through the page reclaim path - `shrink_folio_list` -> `demote_folio_list` -> `migrate_pages` - and is *only* used when memory demotion is active. So these config options are essential to exercise the new code.
*   **`Reasoning:`**: The patch enables `MIGRATE_ASYNC_NON_TEMPORAL_STORES` which leverages non-temporal stores during memory demotion on x86_64. Specifically, page reclaim triggers this new path, so this needs to be investigated. `copy_mc_to_kernel_nt` and `folio_mc_copy_nt` are what actually perform the copying and are, therefore, the key areas to fuzz.

Now, a quick check on architecture: `copy_mc_to_kernel_nt` is *only* defined for x86_64. If the fuzzer somehow ends up running on another architecture, it will fall back to `copy_mc_highpage`, which is basically just `copy_highpage`. But syzkaller primarily runs on x86_64, so that's a non-issue. I'm good to go.

Time to call `set-results`.

{
  "EnableConfigs": [
    "NUMA",
    "MIGRATION"
  ],
  "FocusSymbols": [
    "copy_mc_to_kernel_nt",
    "folio_mc_copy_nt"
  ],
  "Reasoning": "The patch introduces a new memory migration mode `MIGRATE_ASYNC_NON_TEMPORAL_STORES` which uses non-temporal stores for memory demotion on x86_64. This is reachable via page reclaim (`shrink_folio_list` -\u003e `demote_folio_list` -\u003e `migrate_pages`) when memory demotion is enabled. The new functions `copy_mc_to_kernel_nt` and `folio_mc_copy_nt` perform the actual copying and should be focused during fuzzing.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "NUMA",
    "MIGRATION"
  ],
  "FocusSymbols": [
    "copy_mc_to_kernel_nt",
    "folio_mc_copy_nt"
  ],
  "Reasoning": "The patch introduces a new memory migration mode `MIGRATE_ASYNC_NON_TEMPORAL_STORES` which uses non-temporal stores for memory demotion on x86_64. This is reachable via page reclaim (`shrink_folio_list` -\u003e `demote_folio_list` -\u003e `migrate_pages`) when memory demotion is enabled. The new functions `copy_mc_to_kernel_nt` and `folio_mc_copy_nt` perform the actual copying and should be focused during fuzzing.",
  "WorthFuzzing": true
}