AI Trajectory

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Seq	Timestamp	Type	Name	Duration
0/0	2026/11/01 07:36	flow	patch-triage	2m Args: null Results: { "EnableConfigs": [ "SWAP", "SHMEM" ], "FocusSymbols": [ "shrink_folio_list", "folio_batch_pageout", "folio_try_reclaim_free", "folio_try_pageout", "folio_activate_locked", "folio_try_unmap", "reclaim_pages" ], "KMSANReasoning": "The patch refactors pageout and reclamation logic in mm/vmscan.c by batching dirty folio writebacks and modularizing helpers (folio_batch_pageout, folio_try_reclaim_free, folio_try_pageout, folio_activate_locked, folio_try_unmap).\n\nAll newly introduced stack structures and batches (such as struct reclaim_folio_state and pageout_folios) are explicitly zero-initialized and initialized with folio_batch_init() and INIT_LIST_HEAD(). The code does not expose any uninitialized variables, conditional branches on uninitialized state, or data copies to user space (info-leaks).\n\nThe potential risks introduced by this change are memory management logic errors, reference counting inconsistencies, race conditions from unlocking and re-locking folios, or use-after-free conditions. These classes of bugs are thoroughly covered by KASAN, LOCKDEP, and internal VM asserts (VM_WARN_ON/VM_BUG_ON). Because there are no uninitialized memory risks that KMSAN specifically detects, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false, "Reasoning": "The patch modifies core memory management code in mm/vmscan.c, fundamentally changing how dirty folios are handled during page reclaim in shrink_folio_list(). Instead of holding folio locks during pageout, dirty folios are now unlocked, batched in pageout_folios, and processed asynchronously in the newly added folio_batch_pageout(). This introduces an unlocked window where folios can be concurrently modified, remapped, or DMA pinned, necessitating lock re-acquisition and revalidation checks. The patch also adds several VM_WARN_ON runtime assertions and refactors reclaim helpers (folio_try_reclaim_free, folio_activate_locked, folio_try_unmap). These paths are reachable via memory pressure or syscalls such as madvise(MADV_PAGEOUT) and cgroup reclaim, making this highly worthy of fuzzing.", "WorthFuzzing": true }
1/1	2026/11/01 07:36	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit 1d1e051d34c43d5fa528570ffc4e6bd0d73e3e6c\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Sun Nov 1 07:36:48 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/mm/vmscan.c b/mm/vmscan.c\nindex fb9f8f020f6342..1150361e7d5254 100644\n--- a/mm/vmscan.c\n+++ b/mm/vmscan.c\n@@ -1155,23 +1155,322 @@ static bool may_enter_fs(struct folio folio, gfp_t gfp_mask)\n \treturn false;\n }\n \n+/ Activate an isolated, locked folio and account the activation. /\n+static void folio_activate_locked(struct folio folio,\n+\t\tstruct reclaim_stat stat)\n+{\n+\tunsigned int nr_pages = folio_nr_pages(folio);\n+\n+\tVM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);\n+\tVM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);\n+\n+\t/ Not a candidate for swapping, so reclaim swap space. /\n+\tif (folio_test_swapcache(folio) \u0026\u0026\n+\t (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio)))\n+\t\tfolio_free_swap(folio);\n+\tif (!folio_test_mlocked(folio)) {\n+\t\tint type = folio_is_file_lru(folio);\n+\n+\t\tfolio_set_active(folio);\n+\t\tstat-\u003enr_activate[type] += nr_pages;\n+\t\tcount_memcg_folio_events(folio, PGACTIVATE, nr_pages);\n+\t}\n+}\n+\n+/ Results accumulated across a shrink_folio_list() invocation. /\n+struct reclaim_folio_state {\n+\tstruct list_head ret_folios;\n+\tstruct folio_batch free_folios;\n+\tunsigned int nr_reclaimed;\n+};\n+\n+enum folio_reclaim_result {\n+\tFOLIO_RECLAIM_KEEP,\n+\tFOLIO_RECLAIM_ACTIVATE,\n+\tFOLIO_RECLAIM_DONE,\n+};\n+\n+/\n+ * Called with the folio locked. KEEP and ACTIVATE leave it locked and\n+ * owned by the caller. DONE consumes the caller's reference; the caller\n+ * must not access the folio again, even if freeing is deferred.\n+ /\n+static enum folio_reclaim_result folio_try_reclaim_free(struct folio folio,\n+\t\tstruct reclaim_folio_state state,\n+\t\tstruct scan_control sc)\n+{\n+\tconst unsigned int nr_pages = folio_nr_pages(folio);\n+\tstruct address_space mapping = folio_mapping(folio);\n+\n+\t/\n+\t * If the folio has buffers, try to free the buffer mappings\n+\t * associated with this folio. If we succeed we try to free\n+\t * the folio as well.\n+\t \n+\t We do this even if the folio is dirty.\n+\t * filemap_release_folio() does not perform I/O, but it is\n+\t * possible for a folio to have the dirty flag set, but it\n+\t * is actually clean (all its buffers are clean). This\n+\t * happens if the buffers were written out directly, with\n+\t * bh_submit(). ext3 will do this, as well as the blockdev\n+\t * mapping. filemap_release_folio() will discover that\n+\t * cleanness and will drop the buffers and mark the folio\n+\t * clean - it can be freed.\n+\t \n+\t Rarely, folios can have buffers and no -\u003emapping. These\n+\t * are the folios which were not successfully invalidated in\n+\t * truncate_cleanup_folio(). We try to drop those buffers\n+\t * here and if that worked, and the folio is no longer\n+\t * mapped into process address space (refcount == 1) it can\n+\t * be freed. Otherwise, leave the folio on the LRU so it is\n+\t * swappable.\n+\t /\n+\tif (folio_needs_release(folio)) {\n+\t\tif (!filemap_release_folio(folio, sc-\u003egfp_mask))\n+\t\t\treturn FOLIO_RECLAIM_ACTIVATE;\n+\n+\t\tif (!mapping \u0026\u0026 folio_ref_count(folio) == 1) {\n+\t\t\tfolio_unlock(folio);\n+\t\t\tif (folio_put_testzero(folio))\n+\t\t\t\tgoto free_it;\n+\n+\t\t\t/\n+\t\t\t * Rare race with speculative reference. The\n+\t\t\t * speculative reference will free this folio\n+\t\t\t * shortly, so we may increment nr_reclaimed here\n+\t\t\t * and leave it off the LRU.\n+\t\t\t /\n+\t\t\tstate-\u003enr_reclaimed += nr_pages;\n+\t\t\treturn FOLIO_RECLAIM_DONE;\n+\t\t}\n+\t}\n+\n+\tif (folio_test_lazyfree(folio)) {\n+\t\t/ follow __remove_mapping for reference /\n+\t\tif (!folio_ref_freeze(folio, 1))\n+\t\t\treturn FOLIO_RECLAIM_KEEP;\n+\t\t/\n+\t\t * The folio has only one reference left, which is\n+\t\t * from the isolation. After the caller puts the\n+\t\t * folio back on the lru and drops the reference, the\n+\t\t * folio will be freed anyway. It doesn't matter\n+\t\t * which lru it goes on. So we don't bother checking\n+\t\t * the dirty flag here.\n+\t\t /\n+\t\tcount_vm_events(PGLAZYFREED, nr_pages);\n+\t\tcount_memcg_folio_events(folio, PGLAZYFREED, nr_pages);\n+\t} else if (!mapping \|\| !__remove_mapping(mapping, folio, true,\n+\t\t\t\t\t\t\tsc-\u003etarget_mem_cgroup))\n+\t\treturn FOLIO_RECLAIM_KEEP;\n+\n+\tfolio_unlock(folio);\n+free_it:\n+\tVM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);\n+\tstate-\u003enr_reclaimed += nr_pages;\n+\n+\tfolio_unqueue_deferred_split(folio);\n+\tif (folio_batch_add(\u0026state-\u003efree_folios, folio) == 0) {\n+\t\tmem_cgroup_uncharge_folios(\u0026state-\u003efree_folios);\n+\t\ttry_to_unmap_flush();\n+\t\tfree_unref_folios(\u0026state-\u003efree_folios);\n+\t}\n+\treturn FOLIO_RECLAIM_DONE;\n+}\n+\n+enum folio_pageout_result {\n+\tFOLIO_PAGEOUT_KEEP_LOCKED,\n+\tFOLIO_PAGEOUT_KEEP_UNLOCKED,\n+\tFOLIO_PAGEOUT_ACTIVATE,\n+\tFOLIO_PAGEOUT_RECLAIM,\t/ folio is locked, hand it to folio_try_reclaim_free() /\n+};\n+\n /\n- * shrink_folio_list() returns the number of reclaimed pages\n+ * Called with the folio locked. All results leave it locked except\n+ * KEEP_UNLOCKED. The caller retains ownership in every case; RECLAIM\n+ * only allows a subsequent reclaim attempt, it does not free the folio.\n+ /\n+static enum folio_pageout_result folio_try_pageout(struct folio folio,\n+\t\tstruct scan_control sc, struct swap_io_ctx ctx,\n+\t\tstruct list_head folio_list)\n+{\n+\tstruct address_space const mapping = folio_mapping(folio);\n+\tconst unsigned int nr_pages = folio_nr_pages(folio);\n+\n+\tswitch (pageout(ctx, mapping, folio, folio_list)) {\n+\tcase PAGE_ACTIVATE:\n+\t\t/\n+\t\t If shmem folio is split when writeback to swap, the\n+\t\t * tail pages will make their own pass through this\n+\t\t * function and be accounted then. There is no need to\n+\t\t * clamp nr_pages here: folio_activate_locked() derives\n+\t\t * the count from folio_nr_pages() itself.\n+\t\t /\n+\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n+\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n+\t\treturn FOLIO_PAGEOUT_ACTIVATE;\n+\tcase PAGE_KEEP:\n+\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n+\tcase PAGE_SUCCESS:\n+\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n+\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n+\n+\t\tif (folio_test_writeback(folio))\n+\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n+\t\tif (folio_test_dirty(folio))\n+\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n+\n+\t\t/\n+\t\t * A synchronous write - probably a ramdisk. Go ahead\n+\t\t * and try to reclaim the folio.\n+\t\t /\n+\t\tif (!folio_trylock(folio))\n+\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n+\t\tif (folio_test_dirty(folio) \|\| folio_test_writeback(folio))\n+\t\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n+\t\tfallthrough;\n+\tcase PAGE_CLEAN:\n+\t\treturn FOLIO_PAGEOUT_RECLAIM;\n+\t}\n+\tunreachable();\n+}\n+\n+static void folio_batch_pageout(struct folio_batch batch,\n+\t\tstruct reclaim_folio_state state, struct scan_control sc,\n+\t\tstruct reclaim_stat stat, struct swap_io_ctx ctx,\n+\t\tstruct list_head folio_list)\n+{\n+\tunsigned int nr = folio_batch_count(batch);\n+\tunsigned int i;\n+\n+\t/\n+\t * Reuse this private batch to collect the locked folios. Reinit\n+\t * leaves the array intact; nr preserves the original input count.\n+\t * Adding each accepted folio writes at or before the current read\n+\t * index, so entries we have not read yet cannot be overwritten.\n+\t /\n+\tfolio_batch_reinit(batch);\n+\n+\t/\n+\t * Revalidate after taking the lock: writeback may have started, or\n+\t * a swap fault may have remapped the folio and allowed GUP to pin it.\n+\t * Keeping an unmapped folio locked prevents swap faults from mapping\n+\t * it again before the TLB flush and pageout. The lock alone does not\n+\t * exclude GUP, so existing mappings and pins must both be checked.\n+\t /\n+\tfor (i = 0; i \u003c nr; i++) {\n+\t\tstruct folio folio = batch-\u003efolios[i];\n+\n+\t\tif (!folio_trylock(folio)) {\n+\t\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n+\t\t\tcontinue;\n+\t\t}\n+\n+\t\tVM_WARN_ON_FOLIO(folio_test_lru(folio), folio);\n+\n+\t\t/* The folio may have changed while it was unlocked. /\n+\t\tif (folio_test_writeback(folio) \|\| folio_mapped(folio) \|\|\n+\t\t folio_maybe_dma_pinned(folio)) {\n+\t\t\tfolio_unlock(folio);\n+\t\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n+\t\t\tcontinue;\n+\t\t}\n+\n+\t\tfolio_batch_add(batch, folio);\n+\t}\n+\tnr = folio_batch_count(batch);\n+\n+\tif (!nr)\n+\t\treturn;\n+\n+\t/\n+\t * Flush writable TLB entries before any folio in the batch is\n+\t * submitted for I/O.\n+\t /\n+\ttry_to_unmap_flush_dirty();\n+\n+\tfor (i = 0; i \u003c nr; i++) {\n+\t\tstruct folio folio = batch-\u003efolios[i];\n+\n+\t\tswitch (folio_try_pageout(folio, sc, ctx, folio_list)) {\n+\t\tcase FOLIO_PAGEOUT_ACTIVATE:\n+\t\t\tgoto activate_locked;\n+\t\tcase FOLIO_PAGEOUT_KEEP_LOCKED:\n+\t\t\tgoto keep_locked;\n+\t\tcase FOLIO_PAGEOUT_KEEP_UNLOCKED:\n+\t\t\tgoto keep;\n+\t\tcase FOLIO_PAGEOUT_RECLAIM:\n+\t\t\tbreak;\t/* folio is locked; try to free it below /\n+\t\t}\n+\n+\t\tswitch (folio_try_reclaim_free(folio, state, sc)) {\n+\t\tcase FOLIO_RECLAIM_ACTIVATE:\n+\t\t\tgoto activate_locked;\n+\t\tcase FOLIO_RECLAIM_KEEP:\n+\t\t\tgoto keep_locked;\n+\t\tcase FOLIO_RECLAIM_DONE:\n+\t\t\tcontinue;\n+\t\t}\n+activate_locked:\n+\t\tfolio_activate_locked(folio, stat);\n+keep_locked:\n+\t\tfolio_unlock(folio);\n+keep:\n+\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n+\t}\n+\tfolio_batch_reinit(batch);\n+}\n+\n+static bool folio_try_unmap(struct folio folio, struct reclaim_stat stat,\n+\t\tunsigned int nr_pages)\n+{\n+\tenum ttu_flags flags = TTU_BATCH_FLUSH;\n+\tconst bool was_swapbacked = folio_test_swapbacked(folio);\n+\n+\tif (folio_test_pmd_mappable(folio))\n+\t\tflags \|= TTU_SPLIT_HUGE_PMD;\n+\t/\n+\t * Without TTU_SYNC, try_to_unmap will only begin to hold PTL\n+\t * from the first present PTE within a large folio. Some\n+\t * initial PTEs might be skipped due to races with parallel\n+\t * PTE writes in which PTEs can be cleared temporarily before\n+\t * being written new present values. This will lead to a large\n+\t * folio is still mapped while some subpages have been\n+\t * partially unmapped after try_to_unmap; TTU_SYNC helps\n+\t * try_to_unmap acquire PTL from the first PTE, eliminating the\n+\t * influence of temporary PTE values.\n+\t /\n+\tif (folio_test_large(folio))\n+\t\tflags \|= TTU_SYNC;\n+\n+\ttry_to_unmap(folio, flags);\n+\tif (folio_mapped(folio)) {\n+\t\tstat-\u003enr_unmap_fail += nr_pages;\n+\t\tif (!was_swapbacked \u0026\u0026 folio_test_swapbacked(folio))\n+\t\t\tstat-\u003enr_lazyfree_fail += nr_pages;\n+\t\treturn false;\n+\t}\n+\treturn true;\n+}\n+\n+/\n+ * Reclaimed folios are counted in the return value.\n /\n static unsigned int shrink_folio_list(struct list_head folio_list,\n \t\tstruct pglist_data pgdat, struct scan_control sc,\n \t\tstruct reclaim_stat stat, bool ignore_references,\n \t\tstruct mem_cgroup memcg)\n {\n-\tstruct folio_batch free_folios;\n-\tLIST_HEAD(ret_folios);\n+\tstruct reclaim_folio_state state = {};\n+\tstruct folio_batch pageout_folios;\n \tLIST_HEAD(demote_folios);\n-\tunsigned int nr_reclaimed = 0, nr_demoted = 0;\n+\tunsigned int nr_demoted = 0;\n \tunsigned int pgactivate = 0;\n \tbool do_demote_pass;\n \tstruct swap_io_ctx ctx = {};\n \n-\tfolio_batch_init(\u0026free_folios);\n+\tINIT_LIST_HEAD(\u0026state.ret_folios);\n+\tfolio_batch_init(\u0026state.free_folios);\n+\tfolio_batch_init(\u0026pageout_folios);\n \tmemset(stat, 0, sizeof(stat));\n \tcond_resched();\n \tdo_demote_pass = can_demote(pgdat-\u003enode_id, sc, memcg);\n@@ -1433,36 +1732,9 @@ static unsigned int shrink_folio_list(struct list_head folio_list,\n \t\t * The folio is mapped into the page tables of one or more\n \t\t * processes. Try to unmap it here.\n \t\t /\n-\t\tif (folio_mapped(folio)) {\n-\t\t\tenum ttu_flags flags = TTU_BATCH_FLUSH;\n-\t\t\tbool was_swapbacked = folio_test_swapbacked(folio);\n-\n-\t\t\tif (folio_test_pmd_mappable(folio))\n-\t\t\t\tflags \|= TTU_SPLIT_HUGE_PMD;\n-\t\t\t/\n-\t\t\t * Without TTU_SYNC, try_to_unmap will only begin to\n-\t\t\t * hold PTL from the first present PTE within a large\n-\t\t\t * folio. Some initial PTEs might be skipped due to\n-\t\t\t * races with parallel PTE writes in which PTEs can be\n-\t\t\t * cleared temporarily before being written new present\n-\t\t\t * values. This will lead to a large folio is still\n-\t\t\t * mapped while some subpages have been partially\n-\t\t\t * unmapped after try_to_unmap; TTU_SYNC helps\n-\t\t\t * try_to_unmap acquire PTL from the first PTE,\n-\t\t\t * eliminating the influence of temporary PTE values.\n-\t\t\t /\n-\t\t\tif (folio_test_large(folio))\n-\t\t\t\tflags \|= TTU_SYNC;\n-\n-\t\t\ttry_to_unmap(folio, flags);\n-\t\t\tif (folio_mapped(folio)) {\n-\t\t\t\tstat-\u003enr_unmap_fail += nr_pages;\n-\t\t\t\tif (!was_swapbacked \u0026\u0026\n-\t\t\t\t folio_test_swapbacked(folio))\n-\t\t\t\t\tstat-\u003enr_lazyfree_fail += nr_pages;\n-\t\t\t\tgoto activate_locked;\n-\t\t\t}\n-\t\t}\n+\t\tif (folio_mapped(folio) \u0026\u0026\n+\t\t !folio_try_unmap(folio, stat, nr_pages))\n+\t\t\tgoto activate_locked;\n \n \t\t/\n \t\t * Folio is unmapped now so it cannot be newly pinned anymore.\n@@ -1474,7 +1746,6 @@ static unsigned int shrink_folio_list(struct list_head folio_list,\n \t\tif (folio_maybe_dma_pinned(folio))\n \t\t\tgoto activate_locked;\n \n-\t\tmapping = folio_mapping(folio);\n \t\tif (folio_test_dirty(folio)) {\n \t\t\tif (folio_is_file_lru(folio)) {\n \t\t\t\t/\n@@ -1495,164 +1766,53 @@ static unsigned int shrink_folio_list(struct list_head folio_list,\n \t\t\t\tgoto keep_locked;\n \t\t\tif (!sc-\u003emay_writepage)\n \t\t\t\tgoto keep_locked;\n-\n \t\t\t/\n-\t\t\t * Folio is dirty. Flush the TLB if a writable entry\n-\t\t\t * potentially exists to avoid CPU writes after I/O\n-\t\t\t * starts and then write it out here.\n+\t\t\t * Drop the lock so swap faults finding this folio\n+\t\t\t * via swap cache lookup can make progress; the\n+\t\t\t * recheck that this necessitates is documented in\n+\t\t\t * folio_batch_pageout().\n \t\t\t /\n-\t\t\ttry_to_unmap_flush_dirty();\n-\t\t\tswitch (pageout(\u0026ctx, mapping, folio, folio_list)) {\n-\t\t\tcase PAGE_KEEP:\n-\t\t\t\tgoto keep_locked;\n-\t\t\tcase PAGE_ACTIVATE:\n-\t\t\t\t/\n-\t\t\t\t * If shmem folio is split when writeback to swap,\n-\t\t\t\t * the tail pages will make their own pass through\n-\t\t\t\t * this function and be accounted then.\n-\t\t\t\t /\n-\t\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio)) {\n-\t\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n-\t\t\t\t\tnr_pages = 1;\n-\t\t\t\t}\n-\t\t\t\tgoto activate_locked;\n-\t\t\tcase PAGE_SUCCESS:\n-\t\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio)) {\n-\t\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n-\t\t\t\t\tnr_pages = 1;\n-\t\t\t\t}\n-\t\t\t\tif (folio_test_writeback(folio))\n-\t\t\t\t\tgoto keep;\n-\t\t\t\tif (folio_test_dirty(folio))\n-\t\t\t\t\tgoto keep;\n-\n-\t\t\t\t/\n-\t\t\t\t * A synchronous write - probably a ramdisk. Go\n-\t\t\t\t * ahead and try to reclaim the folio.\n-\t\t\t\t /\n-\t\t\t\tif (!folio_trylock(folio))\n-\t\t\t\t\tgoto keep;\n-\t\t\t\tif (folio_test_dirty(folio) \|\|\n-\t\t\t\t folio_test_writeback(folio))\n-\t\t\t\t\tgoto keep_locked;\n-\t\t\t\tmapping = folio_mapping(folio);\n-\t\t\t\tfallthrough;\n-\t\t\tcase PAGE_CLEAN:\n-\t\t\t\t; / try to free the folio below /\n-\t\t\t}\n-\t\t}\n-\n-\t\t/\n-\t\t * If the folio has buffers, try to free the buffer\n-\t\t * mappings associated with this folio. If we succeed\n-\t\t * we try to free the folio as well.\n-\t\t \n-\t\t We do this even if the folio is dirty.\n-\t\t * filemap_release_folio() does not perform I/O, but it\n-\t\t * is possible for a folio to have the dirty flag set,\n-\t\t * but it is actually clean (all its buffers are clean).\n-\t\t * This happens if the buffers were written out directly,\n-\t\t * with bh_submit(). ext3 will do this, as well as\n-\t\t * the blockdev mapping. filemap_release_folio() will\n-\t\t * discover that cleanness and will drop the buffers\n-\t\t * and mark the folio clean - it can be freed.\n-\t\t \n-\t\t Rarely, folios can have buffers and no -\u003emapping.\n-\t\t * These are the folios which were not successfully\n-\t\t * invalidated in truncate_cleanup_folio(). We try to\n-\t\t * drop those buffers here and if that worked, and the\n-\t\t * folio is no longer mapped into process address space\n-\t\t * (refcount == 1) it can be freed. Otherwise, leave\n-\t\t * the folio on the LRU so it is swappable.\n-\t\t /\n-\t\tif (folio_needs_release(folio)) {\n-\t\t\tif (!filemap_release_folio(folio, sc-\u003egfp_mask))\n-\t\t\t\tgoto activate_locked;\n-\t\t\tif (!mapping \u0026\u0026 folio_ref_count(folio) == 1) {\n-\t\t\t\tfolio_unlock(folio);\n-\t\t\t\tif (folio_put_testzero(folio))\n-\t\t\t\t\tgoto free_it;\n-\t\t\t\telse {\n-\t\t\t\t\t/\n-\t\t\t\t\t * rare race with speculative reference.\n-\t\t\t\t\t * the speculative reference will free\n-\t\t\t\t\t * this folio shortly, so we may\n-\t\t\t\t\t * increment nr_reclaimed here (and\n-\t\t\t\t\t * leave it off the LRU).\n-\t\t\t\t\t /\n-\t\t\t\t\tnr_reclaimed += nr_pages;\n-\t\t\t\t\tcontinue;\n-\t\t\t\t}\n-\t\t\t}\n+\t\t\tfolio_unlock(folio);\n+\t\t\tif (!folio_batch_add(\u0026pageout_folios, folio))\n+\t\t\t\tfolio_batch_pageout(\u0026pageout_folios, \u0026state,\n+\t\t\t\t\t\t sc, stat, \u0026ctx, folio_list);\n+\t\t\tcontinue;\n \t\t}\n \n-\t\tif (folio_test_lazyfree(folio)) {\n-\t\t\t/ follow __remove_mapping for reference /\n-\t\t\tif (!folio_ref_freeze(folio, 1))\n-\t\t\t\tgoto keep_locked;\n-\t\t\t/\n-\t\t\t * The folio has only one reference left, which is\n-\t\t\t * from the isolation. After the caller puts the\n-\t\t\t * folio back on the lru and drops the reference, the\n-\t\t\t * folio will be freed anyway. It doesn't matter\n-\t\t\t * which lru it goes on. So we don't bother checking\n-\t\t\t * the dirty flag here.\n-\t\t\t /\n-\t\t\tcount_vm_events(PGLAZYFREED, nr_pages);\n-\t\t\tcount_memcg_folio_events(folio, PGLAZYFREED, nr_pages);\n-\t\t} else if (!mapping \|\| !__remove_mapping(mapping, folio, true,\n-\t\t\t\t\t\t\t sc-\u003etarget_mem_cgroup))\n+\t\tswitch (folio_try_reclaim_free(folio, \u0026state, sc)) {\n+\t\tcase FOLIO_RECLAIM_ACTIVATE:\n+\t\t\tgoto activate_locked;\n+\t\tcase FOLIO_RECLAIM_KEEP:\n \t\t\tgoto keep_locked;\n-\n-\t\tfolio_unlock(folio);\n-free_it:\n-\t\t/\n-\t\t * Folio may get swapped out as a whole, need to account\n-\t\t * all pages in it.\n-\t\t /\n-\t\tnr_reclaimed += nr_pages;\n-\n-\t\tfolio_unqueue_deferred_split(folio);\n-\t\tif (folio_batch_add(\u0026free_folios, folio) == 0) {\n-\t\t\tmem_cgroup_uncharge_folios(\u0026free_folios);\n-\t\t\ttry_to_unmap_flush();\n-\t\t\tfree_unref_folios(\u0026free_folios);\n+\t\tcase FOLIO_RECLAIM_DONE:\n+\t\t\tcontinue;\n \t\t}\n-\t\tcontinue;\n \n activate_locked_split:\n \t\t/\n \t\t * The tail pages that are failed to add into swap cache\n-\t\t * reach here. Fixup nr_scanned and nr_pages.\n+\t\t * reach here. Fixup nr_scanned.\n \t\t /\n-\t\tif (nr_pages \u003e 1) {\n+\t\tif (nr_pages \u003e 1)\n \t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n-\t\t\tnr_pages = 1;\n-\t\t}\n activate_locked:\n-\t\t/ Not a candidate for swapping, so reclaim swap space. /\n-\t\tif (folio_test_swapcache(folio) \u0026\u0026\n-\t\t (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio)))\n-\t\t\tfolio_free_swap(folio);\n-\t\tVM_BUG_ON_FOLIO(folio_test_active(folio), folio);\n-\t\tif (!folio_test_mlocked(folio)) {\n-\t\t\tint type = folio_is_file_lru(folio);\n-\t\t\tfolio_set_active(folio);\n-\t\t\tstat-\u003enr_activate[type] += nr_pages;\n-\t\t\tcount_memcg_folio_events(folio, PGACTIVATE, nr_pages);\n-\t\t}\n+\t\tfolio_activate_locked(folio, stat);\n keep_locked:\n \t\tfolio_unlock(folio);\n keep:\n-\t\tlist_add(\u0026folio-\u003elru, \u0026ret_folios);\n+\t\tlist_add(\u0026folio-\u003elru, \u0026state.ret_folios);\n \t\tVM_BUG_ON_FOLIO(folio_test_lru(folio) \|\|\n \t\t\t\tfolio_test_unevictable(folio), folio);\n \t}\n+\tif (folio_batch_count(\u0026pageout_folios)) {\n+\t\tfolio_batch_pageout(\u0026pageout_folios, \u0026state, sc, stat,\n+\t\t\t\t \u0026ctx, folio_list);\n+\t}\n \t/ 'folio_list' is always empty here /\n \n \t/ Migrate folios selected for demotion /\n \tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\n-\tnr_reclaimed += nr_demoted;\n+\tstate.nr_reclaimed += nr_demoted;\n \tstat-\u003enr_demoted += nr_demoted;\n \t/ Folios that could not be demoted are still in @demote_folios /\n \tif (!list_empty(\u0026demote_folios)) {\n@@ -1683,15 +1843,15 @@ static unsigned int shrink_folio_list(struct list_head folio_list,\n \n \tpgactivate = stat-\u003enr_activate[0] + stat-\u003enr_activate[1];\n \n-\tmem_cgroup_uncharge_folios(\u0026free_folios);\n+\tmem_cgroup_uncharge_folios(\u0026state.free_folios);\n \ttry_to_unmap_flush();\n-\tfree_unref_folios(\u0026free_folios);\n+\tfree_unref_folios(\u0026state.free_folios);\n \n-\tlist_splice(\u0026ret_folios, folio_list);\n+\tlist_splice(\u0026state.ret_folios, folio_list);\n \tcount_vm_events(PGACTIVATE, pgactivate);\n \n \tswap_write_submit(\u0026ctx);\n-\treturn nr_reclaimed;\n+\treturn state.nr_reclaimed;\n }\n \n unsigned int reclaim_clean_pages_from_list(struct zone *zone,\n" }
2/1	2026/11/01 07:36	agent	patch-evaluator	1m Model: core Args: null Results: { "EnableConfigs": [ "SWAP", "SHMEM" ], "FocusSymbols": [ "shrink_folio_list", "folio_batch_pageout", "folio_try_reclaim_free", "folio_try_pageout", "folio_activate_locked", "folio_try_unmap", "reclaim_pages" ], "Reasoning": "The patch modifies core memory management code in mm/vmscan.c, fundamentally changing how dirty folios are handled during page reclaim in shrink_folio_list(). Instead of holding folio locks during pageout, dirty folios are now unlocked, batched in pageout_folios, and processed asynchronously in the newly added folio_batch_pageout(). This introduces an unlocked window where folios can be concurrently modified, remapped, or DMA pinned, necessitating lock re-acquisition and revalidation checks. The patch also adds several VM_WARN_ON runtime assertions and refactors reclaim helpers (folio_try_reclaim_free, folio_activate_locked, folio_try_unmap). These paths are reachable via memory pressure or syscalls such as madvise(MADV_PAGEOUT) and cgroup reclaim, making this highly worthy of fuzzing.", "WorthFuzzing": true } Instruction: You are an expert Linux kernel maintainer and security engineer. Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller. IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in your workspace. Do NOT rely on internal assumptions. You must actively use your code access tools to inspect the actual source code, callers, and surrounding context. ================================================================================ 1. CORE TRIAGE PHILOSOPHY ================================================================================ The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs, and newly triggered assertions introduced by the patch series. - REACHABILITY IS THE PRIMARY GATE: Fuzzing can only discover bugs in code that can actually execute in standard virtualized environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap). If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed, regardless of whether it adds assertions or complex logic. - DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS: Patch authors routinely label changes as "cleanups", "refactorings", or state "No functional change intended". Do NOT take these claims at face value. Code refactorings that rearrange logic, introduce helper functions, or alter state management in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs. If reachable executable code is modified or refactored, it MUST be fuzzed. - NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED: When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON, VM_WARN_ON, BUG_ON, lockdep_assert) in reachable code paths, it enforces new or stricter invariants. Even if the author believes the invariant always holds, fuzzing is essential to verify whether an unusual sequence of operations can violate it. ================================================================================ 2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA) ================================================================================ Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories: - Non-kernel and non-executable changes: * Modifications to Documentation/, comments, or spelling fixes. * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/) that do not affect the compiled kernel image (vmlinux) or kernel modules. * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints that do not alter control flow or data structures. * Build system or Kconfig changes that do not alter compiled C logic. - Structurally unreachable hardware: * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed, ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU. - Unreachable execution paths: * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during physical PCI hot-unplug or manual sysfs driver unbinding. * Code paths exclusive to architectures other than the target architecture. ================================================================================ 3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA) ================================================================================ Return WorthFuzzing=true whenever the patch touches reachable executable code, including: - Core Subsystems: * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/), BPF, scheduler, core networking, VFS, or syscall handling. - Refactorings and Code Cleanups: * Any restructuring of reachable data structures, helper abstractions, or algorithm flows. - Runtime Assertions and Defensive Checks: * Any introduction or alteration of assertions (WARN_ON, VM_WARN_ON, BUG_ON, etc.) in reachable paths. - Reachable Drivers and Protocols: Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.). ================================================================================ 4. EXTRACTING FocusSymbols (PREVENTING DILUTION) ================================================================================ When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer: - AVOID UBIQUITOUS LIFECYCLE HOT-PATHS: Do NOT list generic, ubiquitous functions called by almost every program in the corpus (including, but not limited to: general memory allocators and deallocators, page fault and trap handlers, or core synchronization primitives; this is not an exhaustive list). Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused", which severely dilutes fuzzing effort away from the actual changes. - TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS: List functions that specifically implement the logic being added or altered, or direct API entrypoints for the subsystem feature under review. - HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h): Compiler-inlined static functions (such as static inlines in mm/.h or include/linux/.h) lack distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters. If the changes are primarily in static inline helpers, identify non-static, feature-specific caller functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers). ================================================================================ 5. IDENTIFYING EnableConfigs ================================================================================ Identify any specific CONFIG_ options required to properly compile and reach the modified code: - Inspect Kconfig files and #ifdef guards; do not make assumptions. - Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed. - Strip any '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. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 1d1e051d34c43d5fa528570ffc4e6bd0d73e3e6c Author: syz-cluster <triage@syzkaller.com> Date: Sun Nov 1 07:36:48 2026 +0000 syz-cluster: applied patch under review diff --git a/mm/vmscan.c b/mm/vmscan.c index fb9f8f020f6342..1150361e7d5254 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1155,23 +1155,322 @@ static bool may_enter_fs(struct folio folio, gfp_t gfp_mask) return false; } +/ Activate an isolated, locked folio and account the activation. / +static void folio_activate_locked(struct folio folio, + struct reclaim_stat stat) +{ + unsigned int nr_pages = folio_nr_pages(folio); + + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio); + + / Not a candidate for swapping, so reclaim swap space. / + if (folio_test_swapcache(folio) && + (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio))) + folio_free_swap(folio); + if (!folio_test_mlocked(folio)) { + int type = folio_is_file_lru(folio); + + folio_set_active(folio); + stat->nr_activate[type] += nr_pages; + count_memcg_folio_events(folio, PGACTIVATE, nr_pages); + } +} + +/ Results accumulated across a shrink_folio_list() invocation. / +struct reclaim_folio_state { + struct list_head ret_folios; + struct folio_batch free_folios; + unsigned int nr_reclaimed; +}; + +enum folio_reclaim_result { + FOLIO_RECLAIM_KEEP, + FOLIO_RECLAIM_ACTIVATE, + FOLIO_RECLAIM_DONE, +}; + +/ + * Called with the folio locked. KEEP and ACTIVATE leave it locked and + * owned by the caller. DONE consumes the caller's reference; the caller + * must not access the folio again, even if freeing is deferred. + / +static enum folio_reclaim_result folio_try_reclaim_free(struct folio folio, + struct reclaim_folio_state state, + struct scan_control sc) +{ + const unsigned int nr_pages = folio_nr_pages(folio); + struct address_space mapping = folio_mapping(folio); + + / + * If the folio has buffers, try to free the buffer mappings + * associated with this folio. If we succeed we try to free + * the folio as well. + * + * We do this even if the folio is dirty. + * filemap_release_folio() does not perform I/O, but it is + * possible for a folio to have the dirty flag set, but it + * is actually clean (all its buffers are clean). This + * happens if the buffers were written out directly, with + * bh_submit(). ext3 will do this, as well as the blockdev + * mapping. filemap_release_folio() will discover that + * cleanness and will drop the buffers and mark the folio + * clean - it can be freed. + * + * Rarely, folios can have buffers and no ->mapping. These + * are the folios which were not successfully invalidated in + * truncate_cleanup_folio(). We try to drop those buffers + * here and if that worked, and the folio is no longer + * mapped into process address space (refcount == 1) it can + * be freed. Otherwise, leave the folio on the LRU so it is + * swappable. + / + if (folio_needs_release(folio)) { + if (!filemap_release_folio(folio, sc->gfp_mask)) + return FOLIO_RECLAIM_ACTIVATE; + + if (!mapping && folio_ref_count(folio) == 1) { + folio_unlock(folio); + if (folio_put_testzero(folio)) + goto free_it; + + / + * Rare race with speculative reference. The + * speculative reference will free this folio + * shortly, so we may increment nr_reclaimed here + * and leave it off the LRU. + / + state->nr_reclaimed += nr_pages; + return FOLIO_RECLAIM_DONE; + } + } + + if (folio_test_lazyfree(folio)) { + / follow __remove_mapping for reference / + if (!folio_ref_freeze(folio, 1)) + return FOLIO_RECLAIM_KEEP; + / + * The folio has only one reference left, which is + * from the isolation. After the caller puts the + * folio back on the lru and drops the reference, the + * folio will be freed anyway. It doesn't matter + * which lru it goes on. So we don't bother checking + * the dirty flag here. + / + count_vm_events(PGLAZYFREED, nr_pages); + count_memcg_folio_events(folio, PGLAZYFREED, nr_pages); + } else if (!mapping \|\| !__remove_mapping(mapping, folio, true, + sc->target_mem_cgroup)) + return FOLIO_RECLAIM_KEEP; + + folio_unlock(folio); +free_it: + VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio); + state->nr_reclaimed += nr_pages; + + folio_unqueue_deferred_split(folio); + if (folio_batch_add(&state->free_folios, folio) == 0) { + mem_cgroup_uncharge_folios(&state->free_folios); + try_to_unmap_flush(); + free_unref_folios(&state->free_folios); + } + return FOLIO_RECLAIM_DONE; +} + +enum folio_pageout_result { + FOLIO_PAGEOUT_KEEP_LOCKED, + FOLIO_PAGEOUT_KEEP_UNLOCKED, + FOLIO_PAGEOUT_ACTIVATE, + FOLIO_PAGEOUT_RECLAIM, / folio is locked, hand it to folio_try_reclaim_free() / +}; + / - * shrink_folio_list() returns the number of reclaimed pages + * Called with the folio locked. All results leave it locked except + * KEEP_UNLOCKED. The caller retains ownership in every case; RECLAIM + * only allows a subsequent reclaim attempt, it does not free the folio. + / +static enum folio_pageout_result folio_try_pageout(struct folio folio, + struct scan_control sc, struct swap_io_ctx ctx, + struct list_head folio_list) +{ + struct address_space const mapping = folio_mapping(folio); + const unsigned int nr_pages = folio_nr_pages(folio); + + switch (pageout(ctx, mapping, folio, folio_list)) { + case PAGE_ACTIVATE: + /* + * If shmem folio is split when writeback to swap, the + * tail pages will make their own pass through this + * function and be accounted then. There is no need to + * clamp nr_pages here: folio_activate_locked() derives + * the count from folio_nr_pages() itself. + / + if (nr_pages > 1 && !folio_test_large(folio)) + sc->nr_scanned -= (nr_pages - 1); + return FOLIO_PAGEOUT_ACTIVATE; + case PAGE_KEEP: + return FOLIO_PAGEOUT_KEEP_LOCKED; + case PAGE_SUCCESS: + if (nr_pages > 1 && !folio_test_large(folio)) + sc->nr_scanned -= (nr_pages - 1); + + if (folio_test_writeback(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + if (folio_test_dirty(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + + / + * A synchronous write - probably a ramdisk. Go ahead + * and try to reclaim the folio. + / + if (!folio_trylock(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + if (folio_test_dirty(folio) \|\| folio_test_writeback(folio)) + return FOLIO_PAGEOUT_KEEP_LOCKED; + fallthrough; + case PAGE_CLEAN: + return FOLIO_PAGEOUT_RECLAIM; + } + unreachable(); +} + +static void folio_batch_pageout(struct folio_batch batch, + struct reclaim_folio_state state, struct scan_control sc, + struct reclaim_stat stat, struct swap_io_ctx ctx, + struct list_head folio_list) +{ + unsigned int nr = folio_batch_count(batch); + unsigned int i; + + / + * Reuse this private batch to collect the locked folios. Reinit + * leaves the array intact; nr preserves the original input count. + * Adding each accepted folio writes at or before the current read + * index, so entries we have not read yet cannot be overwritten. + / + folio_batch_reinit(batch); + + / + * Revalidate after taking the lock: writeback may have started, or + * a swap fault may have remapped the folio and allowed GUP to pin it. + * Keeping an unmapped folio locked prevents swap faults from mapping + * it again before the TLB flush and pageout. The lock alone does not + * exclude GUP, so existing mappings and pins must both be checked. + / + for (i = 0; i < nr; i++) { + struct folio folio = batch->folios[i]; + + if (!folio_trylock(folio)) { + list_add(&folio->lru, &state->ret_folios); + continue; + } + + VM_WARN_ON_FOLIO(folio_test_lru(folio), folio); + + /* The folio may have changed while it was unlocked. / + if (folio_test_writeback(folio) \|\| folio_mapped(folio) \|\| + folio_maybe_dma_pinned(folio)) { + folio_unlock(folio); + list_add(&folio->lru, &state->ret_folios); + continue; + } + + folio_batch_add(batch, folio); + } + nr = folio_batch_count(batch); + + if (!nr) + return; + + / + * Flush writable TLB entries before any folio in the batch is + * submitted for I/O. + / + try_to_unmap_flush_dirty(); + + for (i = 0; i < nr; i++) { + struct folio folio = batch->folios[i]; + + switch (folio_try_pageout(folio, sc, ctx, folio_list)) { + case FOLIO_PAGEOUT_ACTIVATE: + goto activate_locked; + case FOLIO_PAGEOUT_KEEP_LOCKED: + goto keep_locked; + case FOLIO_PAGEOUT_KEEP_UNLOCKED: + goto keep; + case FOLIO_PAGEOUT_RECLAIM: + break; /* folio is locked; try to free it below / + } + + switch (folio_try_reclaim_free(folio, state, sc)) { + case FOLIO_RECLAIM_ACTIVATE: + goto activate_locked; + case FOLIO_RECLAIM_KEEP: + goto keep_locked; + case FOLIO_RECLAIM_DONE: + continue; + } +activate_locked: + folio_activate_locked(folio, stat); +keep_locked: + folio_unlock(folio); +keep: + list_add(&folio->lru, &state->ret_folios); + } + folio_batch_reinit(batch); +} + +static bool folio_try_unmap(struct folio folio, struct reclaim_stat stat, + unsigned int nr_pages) +{ + enum ttu_flags flags = TTU_BATCH_FLUSH; + const bool was_swapbacked = folio_test_swapbacked(folio); + + if (folio_test_pmd_mappable(folio)) + flags \|= TTU_SPLIT_HUGE_PMD; + / + * Without TTU_SYNC, try_to_unmap will only begin to hold PTL + * from the first present PTE within a large folio. Some + * initial PTEs might be skipped due to races with parallel + * PTE writes in which PTEs can be cleared temporarily before + * being written new present values. This will lead to a large + * folio is still mapped while some subpages have been + * partially unmapped after try_to_unmap; TTU_SYNC helps + * try_to_unmap acquire PTL from the first PTE, eliminating the + * influence of temporary PTE values. + / + if (folio_test_large(folio)) + flags \|= TTU_SYNC; + + try_to_unmap(folio, flags); + if (folio_mapped(folio)) { + stat->nr_unmap_fail += nr_pages; + if (!was_swapbacked && folio_test_swapbacked(folio)) + stat->nr_lazyfree_fail += nr_pages; + return false; + } + return true; +} + +/ + * Reclaimed folios are counted in the return value. / static unsigned int shrink_folio_list(struct list_head folio_list, struct pglist_data pgdat, struct scan_control sc, struct reclaim_stat stat, bool ignore_references, struct mem_cgroup memcg) { - struct folio_batch free_folios; - LIST_HEAD(ret_folios); + struct reclaim_folio_state state = {}; + struct folio_batch pageout_folios; LIST_HEAD(demote_folios); - unsigned int nr_reclaimed = 0, nr_demoted = 0; + unsigned int nr_demoted = 0; unsigned int pgactivate = 0; bool do_demote_pass; struct swap_io_ctx ctx = {}; - folio_batch_init(&free_folios); + INIT_LIST_HEAD(&state.ret_folios); + folio_batch_init(&state.free_folios); + folio_batch_init(&pageout_folios); memset(stat, 0, sizeof(stat)); cond_resched(); do_demote_pass = can_demote(pgdat->node_id, sc, memcg); @@ -1433,36 +1732,9 @@ static unsigned int shrink_folio_list(struct list_head folio_list, * The folio is mapped into the page tables of one or more * processes. Try to unmap it here. / - if (folio_mapped(folio)) { - enum ttu_flags flags = TTU_BATCH_FLUSH; - bool was_swapbacked = folio_test_swapbacked(folio); - - if (folio_test_pmd_mappable(folio)) - flags \|= TTU_SPLIT_HUGE_PMD; - / - * Without TTU_SYNC, try_to_unmap will only begin to - * hold PTL from the first present PTE within a large - * folio. Some initial PTEs might be skipped due to - * races with parallel PTE writes in which PTEs can be - * cleared temporarily before being written new present - * values. This will lead to a large folio is still - * mapped while some subpages have been partially - * unmapped after try_to_unmap; TTU_SYNC helps - * try_to_unmap acquire PTL from the first PTE, - * eliminating the influence of temporary PTE values. - / - if (folio_test_large(folio)) - flags \|= TTU_SYNC; - - try_to_unmap(folio, flags); - if (folio_mapped(folio)) { - stat->nr_unmap_fail += nr_pages; - if (!was_swapbacked && - folio_test_swapbacked(folio)) - stat->nr_lazyfree_fail += nr_pages; - goto activate_locked; - } - } + if (folio_mapped(folio) && + !folio_try_unmap(folio, stat, nr_pages)) + goto activate_locked; / * Folio is unmapped now so it cannot be newly pinned anymore. @@ -1474,7 +1746,6 @@ static unsigned int shrink_folio_list(struct list_head folio_list, if (folio_maybe_dma_pinned(folio)) goto activate_locked; - mapping = folio_mapping(folio); if (folio_test_dirty(folio)) { if (folio_is_file_lru(folio)) { / @@ -1495,164 +1766,53 @@ static unsigned int shrink_folio_list(struct list_head folio_list, goto keep_locked; if (!sc->may_writepage) goto keep_locked; - / - * Folio is dirty. Flush the TLB if a writable entry - * potentially exists to avoid CPU writes after I/O - * starts and then write it out here. + * Drop the lock so swap faults finding this folio + * via swap cache lookup can make progress; the + * recheck that this necessitates is documented in + * folio_batch_pageout(). / - try_to_unmap_flush_dirty(); - switch (pageout(&ctx, mapping, folio, folio_list)) { - case PAGE_KEEP: - goto keep_locked; - case PAGE_ACTIVATE: - / - * If shmem folio is split when writeback to swap, - * the tail pages will make their own pass through - * this function and be accounted then. - / - if (nr_pages > 1 && !folio_test_large(folio)) { - sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } - goto activate_locked; - case PAGE_SUCCESS: - if (nr_pages > 1 && !folio_test_large(folio)) { - sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } - if (folio_test_writeback(folio)) - goto keep; - if (folio_test_dirty(folio)) - goto keep; - - / - * A synchronous write - probably a ramdisk. Go - * ahead and try to reclaim the folio. - / - if (!folio_trylock(folio)) - goto keep; - if (folio_test_dirty(folio) \|\| - folio_test_writeback(folio)) - goto keep_locked; - mapping = folio_mapping(folio); - fallthrough; - case PAGE_CLEAN: - ; / try to free the folio below / - } - } - - / - * If the folio has buffers, try to free the buffer - * mappings associated with this folio. If we succeed - * we try to free the folio as well. - * - * We do this even if the folio is dirty. - * filemap_release_folio() does not perform I/O, but it - * is possible for a folio to have the dirty flag set, - * but it is actually clean (all its buffers are clean). - * This happens if the buffers were written out directly, - * with bh_submit(). ext3 will do this, as well as - * the blockdev mapping. filemap_release_folio() will - * discover that cleanness and will drop the buffers - * and mark the folio clean - it can be freed. - * - * Rarely, folios can have buffers and no ->mapping. - * These are the folios which were not successfully - * invalidated in truncate_cleanup_folio(). We try to - * drop those buffers here and if that worked, and the - * folio is no longer mapped into process address space - * (refcount == 1) it can be freed. Otherwise, leave - * the folio on the LRU so it is swappable. - / - if (folio_needs_release(folio)) { - if (!filemap_release_folio(folio, sc->gfp_mask)) - goto activate_locked; - if (!mapping && folio_ref_count(folio) == 1) { - folio_unlock(folio); - if (folio_put_testzero(folio)) - goto free_it; - else { - / - * rare race with speculative reference. - * the speculative reference will free - * this folio shortly, so we may - * increment nr_reclaimed here (and - * leave it off the LRU). - / - nr_reclaimed += nr_pages; - continue; - } - } + folio_unlock(folio); + if (!folio_batch_add(&pageout_folios, folio)) + folio_batch_pageout(&pageout_folios, &state, + sc, stat, &ctx, folio_list); + continue; } - if (folio_test_lazyfree(folio)) { - / follow __remove_mapping for reference / - if (!folio_ref_freeze(folio, 1)) - goto keep_locked; - / - * The folio has only one reference left, which is - * from the isolation. After the caller puts the - * folio back on the lru and drops the reference, the - * folio will be freed anyway. It doesn't matter - * which lru it goes on. So we don't bother checking - * the dirty flag here. - / - count_vm_events(PGLAZYFREED, nr_pages); - count_memcg_folio_events(folio, PGLAZYFREED, nr_pages); - } else if (!mapping \|\| !__remove_mapping(mapping, folio, true, - sc->target_mem_cgroup)) + switch (folio_try_reclaim_free(folio, &state, sc)) { + case FOLIO_RECLAIM_ACTIVATE: + goto activate_locked; + case FOLIO_RECLAIM_KEEP: goto keep_locked; - - folio_unlock(folio); -free_it: - / - * Folio may get swapped out as a whole, need to account - * all pages in it. - / - nr_reclaimed += nr_pages; - - folio_unqueue_deferred_split(folio); - if (folio_batch_add(&free_folios, folio) == 0) { - mem_cgroup_uncharge_folios(&free_folios); - try_to_unmap_flush(); - free_unref_folios(&free_folios); + case FOLIO_RECLAIM_DONE: + continue; } - continue; activate_locked_split: / * The tail pages that are failed to add into swap cache - * reach here. Fixup nr_scanned and nr_pages. + * reach here. Fixup nr_scanned. / - if (nr_pages > 1) { + if (nr_pages > 1) sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } activate_locked: - / Not a candidate for swapping, so reclaim swap space. / - if (folio_test_swapcache(folio) && - (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio))) - folio_free_swap(folio); - VM_BUG_ON_FOLIO(folio_test_active(folio), folio); - if (!folio_test_mlocked(folio)) { - int type = folio_is_file_lru(folio); - folio_set_active(folio); - stat->nr_activate[type] += nr_pages; - count_memcg_folio_events(folio, PGACTIVATE, nr_pages); - } + folio_activate_locked(folio, stat); keep_locked: folio_unlock(folio); keep: - list_add(&folio->lru, &ret_folios); + list_add(&folio->lru, &state.ret_folios); VM_BUG_ON_FOLIO(folio_test_lru(folio) \|\| folio_test_unevictable(folio), folio); } + if (folio_batch_count(&pageout_folios)) { + folio_batch_pageout(&pageout_folios, &state, sc, stat, + &ctx, folio_list); + } / 'folio_list' is always empty here / / Migrate folios selected for demotion / nr_demoted = demote_folio_list(&demote_folios, pgdat, memcg); - nr_reclaimed += nr_demoted; + state.nr_reclaimed += nr_demoted; stat->nr_demoted += nr_demoted; / Folios that could not be demoted are still in @demote_folios / if (!list_empty(&demote_folios)) { @@ -1683,15 +1843,15 @@ static unsigned int shrink_folio_list(struct list_head folio_list, pgactivate = stat->nr_activate[0] + stat->nr_activate[1]; - mem_cgroup_uncharge_folios(&free_folios); + mem_cgroup_uncharge_folios(&state.free_folios); try_to_unmap_flush(); - free_unref_folios(&free_folios); + free_unref_folios(&state.free_folios); - list_splice(&ret_folios, folio_list); + list_splice(&state.ret_folios, folio_list); count_vm_events(PGACTIVATE, pgactivate); swap_write_submit(&ctx); - return nr_reclaimed; + return state.nr_reclaimed; } unsigned int reclaim_clean_pages_from_list(struct zone *zone,
3/2	2026/11/01 07:36	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 9697 output: 32 thoughts: 907 Thoughts: Analyzing the VMscan Patch Series Okay, so I'm presented with a patch series applied at HEAD in the kernel repository. My immediate instinct is to get a handle on what's changed and the scope of impact. Given the tools available (grepper, read-file, codesearch-dir-index, and set-results), I need to choose the best path to quickly understand the changes. Let's see... I can't directly check the git log, but I have enough to dive in. The patch touches `mm/vmscan.c`. Alright, that narrows the focus to memory management, which, as an expert, I know is core subsystems, synchronization, locking, and refactoring or code cleanup. A quick scan of the diff reveals a slew of new functions and structures: `folio_activate_locked`, `struct reclaim_folio_state`, `enum folio_reclaim_result`, `folio_try_reclaim_free`, `enum folio_pageout_result`, `folio_try_pageout`, `folio_batch_pageout`, `folio_try_unmap`. Plus a modification to `shrink_folio_list`. `mm/vmscan.c` is definitely a hot spot for page reclaim and related functions. This is good, I can get a feel for how the new functions are used and how they fit into the existing architecture. My focus goes immediately to the `folio_batch_pageout` function, given the context of changes in `shrink_folio_list`. Looking at `shrink_folio_list`, I see a significant architectural shift. Previously, dirty folios were written out immediately while holding the folio lock. Now, the code unlocks dirty folios, batches them using `pageout_folios`, and processes them in batch with `folio_batch_pageout()`! The comment is explicit. In `folio_batch_pageout`, I see the re-locking with `folio_trylock(folio)`, revalidating the folio's state, and then calling `folio_try_pageout()`, `folio_try_reclaim_free()`, and so on. This is a pretty major change to how folio pageout happens during page reclaim! It's moving from lock-intensive, immediate processing to a more batched, asynchronous approach. This likely impacts performance by unlocking the folios so swap faults can make progress. Also it indicates it's adding VM_WARN_ON_ONCE_FOLIO, and other logging statements. Now, I'll need to check the surrounding code in `mm/vmscan.c` to understand the callers and entry points for `shrink_folio_list` to fully grasp the ramifications of this batching approach.
4/2	2026/11/01 07:37	tool	grepper	0m Args: { "Expression": "shrink_folio_list", "PathPrefixes": [ "mm/vmscan.c" ] } Results: { "Output": "mm/vmscan.c=242=static bool root_reclaim(struct scan_control sc)\n--\nmm/vmscan.c-252- completely broken with the legacy memcg and direct stalling in\nmm/vmscan.c:253: * shrink_folio_list() is used for throttling instead, which lacks all the\nmm/vmscan.c-254- * niceties such as fairness, adaptive pausing, bandwidth proportional\n--\nmm/vmscan.c=679=typedef enum {\n--\nmm/vmscan.c-690-/\nmm/vmscan.c:691: pageout is called by shrink_folio_list() for each dirty folio.\nmm/vmscan.c-692- /\n--\nmm/vmscan.c=1159=static void folio_activate_locked(struct folio folio,\n--\nmm/vmscan.c-1179-\nmm/vmscan.c:1180:/* Results accumulated across a shrink_folio_list() invocation. /\nmm/vmscan.c-1181-struct reclaim_folio_state {\n--\nmm/vmscan.c=1423=static bool folio_try_unmap(struct folio folio, struct reclaim_stat stat,\n--\nmm/vmscan.c-1457- /\nmm/vmscan.c:1458:static unsigned int shrink_folio_list(struct list_head folio_list,\nmm/vmscan.c-1459-\t\tstruct pglist_data pgdat, struct scan_control sc,\n--\nmm/vmscan.c=1857=unsigned int reclaim_clean_pages_from_list(struct zone zone,\n--\nmm/vmscan.c-1887-\tnoreclaim_flag = memalloc_noreclaim_save();\nmm/vmscan.c:1888:\tnr_reclaimed = shrink_folio_list(\u0026clean_folios, zone-\u003ezone_pgdat, \u0026sc,\nmm/vmscan.c-1889-\t\t\t\t\t\u0026stat, true, NULL);\n--\nmm/vmscan.c=2222=static void handle_reclaim_writeback(unsigned long nr_taken,\n--\nmm/vmscan.c-2242-\t\t * the kernel flusher here and later waiting on folios\nmm/vmscan.c:2243:\t\t * which are in writeback to finish (see shrink_folio_list()).\nmm/vmscan.c-2244-\t\t \n--\nmm/vmscan.c=2264=static unsigned long shrink_inactive_list(unsigned long nr_to_scan,\n--\nmm/vmscan.c-2307-\nmm/vmscan.c:2308:\tnr_reclaimed = shrink_folio_list(\u0026folio_list, pgdat, sc, \u0026stat, false,\nmm/vmscan.c-2309-\t\t\t\t\t lruvec_memcg(lruvec));\n--\nmm/vmscan.c=2435=static unsigned int reclaim_folio_list(struct list_head folio_list,\n--\nmm/vmscan.c-2448-\nmm/vmscan.c:2449:\tnr_reclaimed = shrink_folio_list(folio_list, pgdat, \u0026sc, \u0026stat, true, NULL);\nmm/vmscan.c-2450-\twhile (!list_empty(folio_list)) {\n--\nmm/vmscan.c=4551=static void lru_gen_age_node(struct pglist_data pgdat, struct scan_control sc)\n--\nmm/vmscan.c-4591-/\nmm/vmscan.c:4592: This function exploits spatial locality when shrink_folio_list() walks the\nmm/vmscan.c-4593- * rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages. If\n--\nmm/vmscan.c=5220=static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,\n--\nmm/vmscan.c-5257-retry:\nmm/vmscan.c:5258:\treclaimed = shrink_folio_list(\u0026list, pgdat, sc, \u0026stat, false, memcg);\nmm/vmscan.c-5259-\tsc-\u003enr_reclaimed += reclaimed;\n" }
5/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 12297 output: 29 thoughts: 35 Thoughts: Okay, here's my attempt at summarizing those thoughts from an expert's perspective, using the first person and aiming for a fulsome explanation: Analyzing Memory Reclamation Functions Alright, let's dive in. I need to get a handle on how memory is actually being freed up and returned. My primary focus right now is understanding the flow and impact of `reclaim_folio_list`, `shrink_inactive_list`, and `reclaim_clean_pages_from_list`. These functions are central to effective memory management in the system, and I want to pinpoint their relationships and the circumstances under which they are invoked. I suspect that understanding where these are being called from will provide valuable clues about the memory reclaim strategy employed. Are they invoked in response to explicit memory pressure, or are they proactively cleaning up resources? I should also examine if any of these are the primary drivers or if they are complementary. What are the calling contexts? Are they triggered by page faults, timers, background processes, or something else entirely? I'm also curious about the specific lists or data structures they operate on. What are the "folio lists," the "inactive lists," and the "clean pages from list" really representing? Understanding the granularity and organization of these lists is critical. Are these per-NUMA node, per-process, or global structures? Are they related to the page cache, anonymous memory, or both? Are there any ordering or prioritization schemes at play? And, does this vary for different architectures or workloads? Furthermore, I need to evaluate the implications of their actions. What are the performance costs associated with reclaiming memory? Are there any locking or synchronization considerations I should be aware of? Are there situations where these functions could be a bottleneck, or trigger cascading effects on other system components? Are there any potential trade-offs being made between performance and memory utilization? And do they play nicely with other memory management mechanisms? I need to understand the design choices, which is where the context of their calls matters. Knowing where they are called will shed light on the design choices made, and if there are any areas for optimization. This will help me to gain a deeper insight into how the kernel balances its resource utilization.
6/2	2026/11/01 07:37	tool	grepper	0m Args: { "Expression": "reclaim_folio_list", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/vmscan.c=2346=static void shrink_active_list(unsigned long nr_to_scan,\n--\nmm/vmscan.c-2434-\nmm/vmscan.c:2435:static unsigned int reclaim_folio_list(struct list_head folio_list,\nmm/vmscan.c-2436-\t\t\t\t struct pglist_data pgdat)\n--\nmm/vmscan.c=2460=unsigned long reclaim_pages(struct list_head *folio_list)\n--\nmm/vmscan.c-2481-\nmm/vmscan.c:2482:\t\tnr_reclaimed += reclaim_folio_list(\u0026node_folio_list, NODE_DATA(nid));\nmm/vmscan.c-2483-\t\tnid = folio_nid(lru_to_folio(folio_list));\n--\nmm/vmscan.c-2485-\nmm/vmscan.c:2486:\tnr_reclaimed += reclaim_folio_list(\u0026node_folio_list, NODE_DATA(nid));\nmm/vmscan.c-2487-\n" }
7/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 13107 output: 28 thoughts: 12 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: Analyzing the Callers of `reclaim_pages` Alright, so the task at hand is to understand how `reclaim_pages` is being used, specifically in this context, whatever that is. My immediate instinct is to identify all the call sites. We're talking about memory management, so any use of `reclaim_pages` is significant. I need to trace the execution flow, understand the logic that leads to that call, and the invariants that are assumed to be true when it's invoked. This isn't just about finding the function calls themselves; it's about the why and the when. I'll need to consider: * Context: What subsystem or module is using this function? Is it the page cache, the VM, a device driver, or something else entirely? * Purpose: What's the reason for reclaiming pages in each caller? Is it for memory pressure, resource cleanup, or something more specific? * Synchronization: What locking primitives are involved around the calls? Spinlocks, mutexes, RCU? Understanding the concurrency model is paramount to avoiding subtle bugs like deadlocks or data races. * Page State: What assumptions are made about the state of the pages being reclaimed? Are they clean, dirty, active, inactive, mapped or unmapped? This has important implications on performance and correctness. * Side Effects: Are there any other data structures or resources that are affected by this reclamation process? For example, are there any interactions with other memory management functions or subsystems? Ultimately, this exercise is about understanding the implications of each call to `reclaim_pages`. It's not just about a code search; it's about building a comprehensive mental model of the system's memory reclamation behavior. I'll need to dig into the surrounding code, identify the critical paths, and anticipate potential issues. I'll also be on the lookout for patterns – are there common ways to trigger this reclamation that I can exploit for performance optimization or, conversely, that might be sources of contention? Knowing this information will give me a solid base of understanding for any future work on the system's memory management behavior.
8/2	2026/11/01 07:37	tool	grepper	0m Args: { "Expression": "reclaim_pages\\(", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/damon/paddr.c=244=static unsigned long damon_pa_pageout(struct damon_region r,\n--\nmm/damon/paddr.c-295-\t\tdamos_destroy_filter(filter);\nmm/damon/paddr.c:296:\tapplied = reclaim_pages(\u0026folio_list);\nmm/damon/paddr.c-297-\tcond_resched();\n--\nmm/internal.h=1198=extern unsigned long __must_check vm_mmap_pgoff(struct file , unsigned long,\n--\nmm/internal.h-1201-\nmm/internal.h:1202:unsigned long reclaim_pages(struct list_head folio_list);\nmm/internal.h-1203-unsigned int reclaim_clean_pages_from_list(struct zone zone,\n--\nmm/madvise.c=363=static int madvise_cold_or_pageout_pte_range(pmd_t pmd,\n--\nmm/madvise.c-452-\t\tif (pageout)\nmm/madvise.c:453:\t\t\treclaim_pages(\u0026folio_list);\nmm/madvise.c-454-\t\tcond_resched();\n--\nmm/madvise.c-573-\tif (pageout)\nmm/madvise.c:574:\t\treclaim_pages(\u0026folio_list);\nmm/madvise.c-575-\tcond_resched();\n--\nmm/vmscan.c=2435=static unsigned int reclaim_folio_list(struct list_head folio_list,\n--\nmm/vmscan.c-2454-\t}\nmm/vmscan.c:2455:\ttrace_mm_vmscan_reclaim_pages(pgdat-\u003enode_id, sc.nr_scanned, nr_reclaimed, \u0026stat);\nmm/vmscan.c-2456-\n--\nmm/vmscan.c-2459-\nmm/vmscan.c:2460:unsigned long reclaim_pages(struct list_head *folio_list)\nmm/vmscan.c-2461-{\n" }
9/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 14190 output: 35 thoughts: 1418 Thoughts: Analyzing Memory Reclaim Logic and Identifying Fuzzing Targets Okay, so I'm looking at this code and immediately my expert brain starts to map out the memory reclaim pathways. It's clear that `madvise(..., MADV_PAGEOUT)` kicks things off, calling `reclaim_pages`, which then cascades through `reclaim_folio_list` and finally `shrink_folio_list`. We also have `shrink_inactive_list` being called during regular reclaim and kswapd, and multi-gen LRU's `evict_folios` also utilizes `shrink_folio_list`. Finally cgroup memory reclaim plays a role here with `memory.reclaim`. My initial thought is to analyze the functions that were added or significantly altered, specifically: `shrink_folio_list`, `folio_batch_pageout`, `folio_try_reclaim_free`, `folio_try_pageout`, `folio_try_unmap`, and `folio_activate_locked`. My gut tells me some of these statics are key. Now, a crucial question arises: Are these static functions visible to the kernel symbol table (kallsyms), or are they inlined? This is where the fuzzing guidelines come in. The focus is to avoid targeting ubiquitous functions. So, I dig in and see that `shrink_folio_list` is definitely not inlined and is called by several key reclaim paths. Meanwhile, `folio_batch_pageout`, `folio_try_reclaim_free`, `folio_try_pageout` are all static functions defined in `.c` files. This is important: Static functions in `.c` files, if not inlined, are distinct symbols in the kernel. I need to confirm that `shrink_folio_list` itself isn't a ubiquitous hot-path, given its size and call sites. Is it something that almost every program in the corpus is using? No! `shrink_folio_list` is specific to page reclaim, which is a good thing for fuzzing purposes. It is a highly specific function called during page reclaim / memory reclaim (when the system is low on memory or during memory cgroup reclaim or when `madvise(MADV_PAGEOUT)` is used). It's not a core allocator or handler, so it's a good candidate. `folio_batch_pageout` is specifically part of this patch implementing batching logic. So, `shrink_folio_list` is definitely not inlined (it's called from so many places and it's huge!), and therefore a good focus. `folio_batch_pageout` is also a strong candidate as the new function responsible for batching. The others are worth considering as well, but now let's inspect the patch details and the code around `folio_batch_pageout` and `folio_try_pageout` in `mm/vmscan.c`. I need to fully understand the functionality of the patch.
10/2	2026/11/01 07:37	tool	read-file	0m Args: { "File": "mm/vmscan.c", "FirstLine": 1155, "LineCount": 80 } Results: { "Contents": "1155:\t\treturn false;\n1156:\t}\n1157:\t\n1158:\t/* Activate an isolated, locked folio and account the activation. /\n1159:\tstatic void folio_activate_locked(struct folio folio,\n1160:\t\t\tstruct reclaim_stat stat)\n1161:\t{\n1162:\t\tunsigned int nr_pages = folio_nr_pages(folio);\n1163:\t\n1164:\t\tVM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);\n1165:\t\tVM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);\n1166:\t\n1167:\t\t/ Not a candidate for swapping, so reclaim swap space. /\n1168:\t\tif (folio_test_swapcache(folio) \u0026\u0026\n1169:\t\t (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio)))\n1170:\t\t\tfolio_free_swap(folio);\n1171:\t\tif (!folio_test_mlocked(folio)) {\n1172:\t\t\tint type = folio_is_file_lru(folio);\n1173:\t\n1174:\t\t\tfolio_set_active(folio);\n1175:\t\t\tstat-\u003enr_activate[type] += nr_pages;\n1176:\t\t\tcount_memcg_folio_events(folio, PGACTIVATE, nr_pages);\n1177:\t\t}\n1178:\t}\n1179:\t\n1180:\t/ Results accumulated across a shrink_folio_list() invocation. /\n1181:\tstruct reclaim_folio_state {\n1182:\t\tstruct list_head ret_folios;\n1183:\t\tstruct folio_batch free_folios;\n1184:\t\tunsigned int nr_reclaimed;\n1185:\t};\n1186:\t\n1187:\tenum folio_reclaim_result {\n1188:\t\tFOLIO_RECLAIM_KEEP,\n1189:\t\tFOLIO_RECLAIM_ACTIVATE,\n1190:\t\tFOLIO_RECLAIM_DONE,\n1191:\t};\n1192:\t\n1193:\t/\n1194:\t * Called with the folio locked. KEEP and ACTIVATE leave it locked and\n1195:\t * owned by the caller. DONE consumes the caller's reference; the caller\n1196:\t * must not access the folio again, even if freeing is deferred.\n1197:\t /\n1198:\tstatic enum folio_reclaim_result folio_try_reclaim_free(struct folio folio,\n1199:\t\t\tstruct reclaim_folio_state state,\n1200:\t\t\tstruct scan_control sc)\n1201:\t{\n1202:\t\tconst unsigned int nr_pages = folio_nr_pages(folio);\n1203:\t\tstruct address_space mapping = folio_mapping(folio);\n1204:\t\n1205:\t\t/\n1206:\t\t * If the folio has buffers, try to free the buffer mappings\n1207:\t\t * associated with this folio. If we succeed we try to free\n1208:\t\t * the folio as well.\n1209:\t\t \n1210:\t\t We do this even if the folio is dirty.\n1211:\t\t * filemap_release_folio() does not perform I/O, but it is\n1212:\t\t * possible for a folio to have the dirty flag set, but it\n1213:\t\t * is actually clean (all its buffers are clean). This\n1214:\t\t * happens if the buffers were written out directly, with\n1215:\t\t * bh_submit(). ext3 will do this, as well as the blockdev\n1216:\t\t * mapping. filemap_release_folio() will discover that\n1217:\t\t * cleanness and will drop the buffers and mark the folio\n1218:\t\t * clean - it can be freed.\n1219:\t\t \n1220:\t\t Rarely, folios can have buffers and no -\u003emapping. These\n1221:\t\t * are the folios which were not successfully invalidated in\n1222:\t\t * truncate_cleanup_folio(). We try to drop those buffers\n1223:\t\t * here and if that worked, and the folio is no longer\n1224:\t\t * mapped into process address space (refcount == 1) it can\n1225:\t\t * be freed. Otherwise, leave the folio on the LRU so it is\n1226:\t\t * swappable.\n1227:\t\t */\n1228:\t\tif (folio_needs_release(folio)) {\n1229:\t\t\tif (!filemap_release_folio(folio, sc-\u003egfp_mask))\n1230:\t\t\t\treturn FOLIO_RECLAIM_ACTIVATE;\n1231:\t\n1232:\t\t\tif (!mapping \u0026\u0026 folio_ref_count(folio) == 1) {\n1233:\t\t\t\tfolio_unlock(folio);\n1234:\t\t\t\tif (folio_put_testzero(folio))\n" }
11/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17591 output: 36 thoughts: 15 Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own: Diving into the `mm/vmscan.c` Code Alright, time to get my hands dirty. I need to understand this memory management process better, and it looks like `mm/vmscan.c` is the key. Let's see what gems are hidden further down in this file. I'm expecting to find insights into the core of how the virtual memory scanner works. Perhaps I can find the nuances of page reclamation or maybe even some performance bottlenecks I could optimize. Let's see what we can find. I'm already formulating some questions in my head: What specific data structures does it interact with? What are the key algorithms? Where's the heart of the LRU-based scanning happening? Time to put on my reading glasses, and dive in.
12/2	2026/11/01 07:37	tool	read-file	0m Args: { "File": "mm/vmscan.c", "FirstLine": 1235, "LineCount": 100 } Results: { "Contents": "1235:\t\t\t\t\tgoto free_it;\n1236:\t\n1237:\t\t\t\t/\n1238:\t\t\t\t Rare race with speculative reference. The\n1239:\t\t\t\t * speculative reference will free this folio\n1240:\t\t\t\t * shortly, so we may increment nr_reclaimed here\n1241:\t\t\t\t * and leave it off the LRU.\n1242:\t\t\t\t /\n1243:\t\t\t\tstate-\u003enr_reclaimed += nr_pages;\n1244:\t\t\t\treturn FOLIO_RECLAIM_DONE;\n1245:\t\t\t}\n1246:\t\t}\n1247:\t\n1248:\t\tif (folio_test_lazyfree(folio)) {\n1249:\t\t\t/ follow __remove_mapping for reference /\n1250:\t\t\tif (!folio_ref_freeze(folio, 1))\n1251:\t\t\t\treturn FOLIO_RECLAIM_KEEP;\n1252:\t\t\t/\n1253:\t\t\t * The folio has only one reference left, which is\n1254:\t\t\t * from the isolation. After the caller puts the\n1255:\t\t\t * folio back on the lru and drops the reference, the\n1256:\t\t\t * folio will be freed anyway. It doesn't matter\n1257:\t\t\t * which lru it goes on. So we don't bother checking\n1258:\t\t\t * the dirty flag here.\n1259:\t\t\t /\n1260:\t\t\tcount_vm_events(PGLAZYFREED, nr_pages);\n1261:\t\t\tcount_memcg_folio_events(folio, PGLAZYFREED, nr_pages);\n1262:\t\t} else if (!mapping \|\| !__remove_mapping(mapping, folio, true,\n1263:\t\t\t\t\t\t\t\tsc-\u003etarget_mem_cgroup))\n1264:\t\t\treturn FOLIO_RECLAIM_KEEP;\n1265:\t\n1266:\t\tfolio_unlock(folio);\n1267:\tfree_it:\n1268:\t\tVM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);\n1269:\t\tstate-\u003enr_reclaimed += nr_pages;\n1270:\t\n1271:\t\tfolio_unqueue_deferred_split(folio);\n1272:\t\tif (folio_batch_add(\u0026state-\u003efree_folios, folio) == 0) {\n1273:\t\t\tmem_cgroup_uncharge_folios(\u0026state-\u003efree_folios);\n1274:\t\t\ttry_to_unmap_flush();\n1275:\t\t\tfree_unref_folios(\u0026state-\u003efree_folios);\n1276:\t\t}\n1277:\t\treturn FOLIO_RECLAIM_DONE;\n1278:\t}\n1279:\t\n1280:\tenum folio_pageout_result {\n1281:\t\tFOLIO_PAGEOUT_KEEP_LOCKED,\n1282:\t\tFOLIO_PAGEOUT_KEEP_UNLOCKED,\n1283:\t\tFOLIO_PAGEOUT_ACTIVATE,\n1284:\t\tFOLIO_PAGEOUT_RECLAIM,\t/ folio is locked, hand it to folio_try_reclaim_free() /\n1285:\t};\n1286:\t\n1287:\t/\n1288:\t * Called with the folio locked. All results leave it locked except\n1289:\t * KEEP_UNLOCKED. The caller retains ownership in every case; RECLAIM\n1290:\t * only allows a subsequent reclaim attempt, it does not free the folio.\n1291:\t /\n1292:\tstatic enum folio_pageout_result folio_try_pageout(struct folio folio,\n1293:\t\t\tstruct scan_control sc, struct swap_io_ctx ctx,\n1294:\t\t\tstruct list_head folio_list)\n1295:\t{\n1296:\t\tstruct address_space const mapping = folio_mapping(folio);\n1297:\t\tconst unsigned int nr_pages = folio_nr_pages(folio);\n1298:\t\n1299:\t\tswitch (pageout(ctx, mapping, folio, folio_list)) {\n1300:\t\tcase PAGE_ACTIVATE:\n1301:\t\t\t/\n1302:\t\t\t If shmem folio is split when writeback to swap, the\n1303:\t\t\t * tail pages will make their own pass through this\n1304:\t\t\t * function and be accounted then. There is no need to\n1305:\t\t\t * clamp nr_pages here: folio_activate_locked() derives\n1306:\t\t\t * the count from folio_nr_pages() itself.\n1307:\t\t\t /\n1308:\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n1309:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1310:\t\t\treturn FOLIO_PAGEOUT_ACTIVATE;\n1311:\t\tcase PAGE_KEEP:\n1312:\t\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n1313:\t\tcase PAGE_SUCCESS:\n1314:\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n1315:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1316:\t\n1317:\t\t\tif (folio_test_writeback(folio))\n1318:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1319:\t\t\tif (folio_test_dirty(folio))\n1320:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1321:\t\n1322:\t\t\t/\n1323:\t\t\t * A synchronous write - probably a ramdisk. Go ahead\n1324:\t\t\t * and try to reclaim the folio.\n1325:\t\t\t */\n1326:\t\t\tif (!folio_trylock(folio))\n1327:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1328:\t\t\tif (folio_test_dirty(folio) \|\| folio_test_writeback(folio))\n1329:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n1330:\t\t\tfallthrough;\n1331:\t\tcase PAGE_CLEAN:\n1332:\t\t\treturn FOLIO_PAGEOUT_RECLAIM;\n1333:\t\t}\n1334:\t\tunreachable();\n" }
13/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19445 output: 36 thoughts: 18 Thoughts: Okay, here's the summary, rendered as a first-person thought process, keeping in mind the user is an expert: Deep Dive Incoming: Targeted Lines for Focused Analysis Alright, I'm going to take a deeper look. I need to zero in on lines 1335 through 1440. Given my existing understanding of [implied field - let's say, computational linguistics, since the user is an expert], that specific segment likely contains critical details regarding [mention possible topic based on context clues or assumed expertise]. I anticipate [make a prediction about the content, e.g., a specific algorithm, a data structure, a key finding, a problematic edge case]. Focusing on this range should allow me to quickly assess [mention goal e.g., the validity of a claim, the novelty of an approach, the implications of a result] without getting bogged down in extraneous detail. Let's see if my initial assessment holds. Time to dissect and analyze.
14/2	2026/11/01 07:37	tool	read-file	0m Args: { "File": "mm/vmscan.c", "FirstLine": 1335, "LineCount": 100 } Results: { "Contents": "1335:\t}\n1336:\t\n1337:\tstatic void folio_batch_pageout(struct folio_batch batch,\n1338:\t\t\tstruct reclaim_folio_state state, struct scan_control sc,\n1339:\t\t\tstruct reclaim_stat stat, struct swap_io_ctx ctx,\n1340:\t\t\tstruct list_head folio_list)\n1341:\t{\n1342:\t\tunsigned int nr = folio_batch_count(batch);\n1343:\t\tunsigned int i;\n1344:\t\n1345:\t\t/\n1346:\t\t Reuse this private batch to collect the locked folios. Reinit\n1347:\t\t * leaves the array intact; nr preserves the original input count.\n1348:\t\t * Adding each accepted folio writes at or before the current read\n1349:\t\t * index, so entries we have not read yet cannot be overwritten.\n1350:\t\t /\n1351:\t\tfolio_batch_reinit(batch);\n1352:\t\n1353:\t\t/\n1354:\t\t * Revalidate after taking the lock: writeback may have started, or\n1355:\t\t * a swap fault may have remapped the folio and allowed GUP to pin it.\n1356:\t\t * Keeping an unmapped folio locked prevents swap faults from mapping\n1357:\t\t * it again before the TLB flush and pageout. The lock alone does not\n1358:\t\t * exclude GUP, so existing mappings and pins must both be checked.\n1359:\t\t /\n1360:\t\tfor (i = 0; i \u003c nr; i++) {\n1361:\t\t\tstruct folio folio = batch-\u003efolios[i];\n1362:\t\n1363:\t\t\tif (!folio_trylock(folio)) {\n1364:\t\t\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n1365:\t\t\t\tcontinue;\n1366:\t\t\t}\n1367:\t\n1368:\t\t\tVM_WARN_ON_FOLIO(folio_test_lru(folio), folio);\n1369:\t\n1370:\t\t\t/* The folio may have changed while it was unlocked. /\n1371:\t\t\tif (folio_test_writeback(folio) \|\| folio_mapped(folio) \|\|\n1372:\t\t\t folio_maybe_dma_pinned(folio)) {\n1373:\t\t\t\tfolio_unlock(folio);\n1374:\t\t\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n1375:\t\t\t\tcontinue;\n1376:\t\t\t}\n1377:\t\n1378:\t\t\tfolio_batch_add(batch, folio);\n1379:\t\t}\n1380:\t\tnr = folio_batch_count(batch);\n1381:\t\n1382:\t\tif (!nr)\n1383:\t\t\treturn;\n1384:\t\n1385:\t\t/\n1386:\t\t * Flush writable TLB entries before any folio in the batch is\n1387:\t\t * submitted for I/O.\n1388:\t\t /\n1389:\t\ttry_to_unmap_flush_dirty();\n1390:\t\n1391:\t\tfor (i = 0; i \u003c nr; i++) {\n1392:\t\t\tstruct folio folio = batch-\u003efolios[i];\n1393:\t\n1394:\t\t\tswitch (folio_try_pageout(folio, sc, ctx, folio_list)) {\n1395:\t\t\tcase FOLIO_PAGEOUT_ACTIVATE:\n1396:\t\t\t\tgoto activate_locked;\n1397:\t\t\tcase FOLIO_PAGEOUT_KEEP_LOCKED:\n1398:\t\t\t\tgoto keep_locked;\n1399:\t\t\tcase FOLIO_PAGEOUT_KEEP_UNLOCKED:\n1400:\t\t\t\tgoto keep;\n1401:\t\t\tcase FOLIO_PAGEOUT_RECLAIM:\n1402:\t\t\t\tbreak;\t/* folio is locked; try to free it below /\n1403:\t\t\t}\n1404:\t\n1405:\t\t\tswitch (folio_try_reclaim_free(folio, state, sc)) {\n1406:\t\t\tcase FOLIO_RECLAIM_ACTIVATE:\n1407:\t\t\t\tgoto activate_locked;\n1408:\t\t\tcase FOLIO_RECLAIM_KEEP:\n1409:\t\t\t\tgoto keep_locked;\n1410:\t\t\tcase FOLIO_RECLAIM_DONE:\n1411:\t\t\t\tcontinue;\n1412:\t\t\t}\n1413:\tactivate_locked:\n1414:\t\t\tfolio_activate_locked(folio, stat);\n1415:\tkeep_locked:\n1416:\t\t\tfolio_unlock(folio);\n1417:\tkeep:\n1418:\t\t\tlist_add(\u0026folio-\u003elru, \u0026state-\u003eret_folios);\n1419:\t\t}\n1420:\t\tfolio_batch_reinit(batch);\n1421:\t}\n1422:\t\n1423:\tstatic bool folio_try_unmap(struct folio folio, struct reclaim_stat stat,\n1424:\t\t\tunsigned int nr_pages)\n1425:\t{\n1426:\t\tenum ttu_flags flags = TTU_BATCH_FLUSH;\n1427:\t\tconst bool was_swapbacked = folio_test_swapbacked(folio);\n1428:\t\n1429:\t\tif (folio_test_pmd_mappable(folio))\n1430:\t\t\tflags \|= TTU_SPLIT_HUGE_PMD;\n1431:\t\t/\n1432:\t\t * Without TTU_SYNC, try_to_unmap will only begin to hold PTL\n1433:\t\t * from the first present PTE within a large folio. Some\n1434:\t\t * initial PTEs might be skipped due to races with parallel\n" }
15/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 21201 output: 27 thoughts: 1707 Thoughts: Page Reclaim Logic Analysis: Worthy of Fuzzing Okay, this is a significant change in the page reclaim logic, let's dive in. First, based on the commit, this is a "syz-cluster: applied patch under review". Now, let's ascertain if this is a suitable target for fuzzing. 1. Reachability: `mm/vmscan.c` is the heart of page reclaim, so definitely reachable. It’s triggered under memory pressure (kswapd, direct reclaim, shrinkers) and via user-space syscalls like `madvise(MADV_PAGEOUT)`, `madvise(MADV_COLD)`, `process_madvise(MADV_PAGEOUT)`, cgroup memory controller (`memory.reclaim`), and DAMON (Data Access Monitor pageout). So it's used everywhere. 2. Code Execution: Yes, this patch absolutely touches executable code within `mm/vmscan.c`. It's restructuring `shrink_folio_list`, specifically by batching dirty folios in `pageout_folios` for `folio_batch_pageout`. This new batching approach introduces a locking window – unlocking and re-locking folios with `folio_trylock`. This means concurrency issues with swap faults, GUP, writeback, etc., are now explicitly in the mix, begging for careful testing. The new assertions added: `VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);`, `VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);`, `VM_WARN_ON_FOLIO(folio_test_lru(folio), folio);`, and `VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);` – are strong indicators that this code path is now safety-critical. Based on this, `WorthFuzzing` is unequivocally `true`. Now, the crucial part: determining the `FocusSymbols`. Let's adhere to the rules. We need specific feature logic and entrypoints, avoiding ubiquitous lifecycle paths. The key functions in this patch are: * `folio_batch_pageout` (new static function) * `folio_try_reclaim_free` (new static function) * `folio_try_pageout` (new static function) * `folio_activate_locked` (new static function) * `folio_try_unmap` (new static function) * `shrink_folio_list` (modified static function) And some non-static callers: * `reclaim_pages` (exported in `mm/internal.h`, called by `madvise`) * `shrink_inactive_list` (in `mm/vmscan.c`, called by `shrink_list`) * `reclaim_clean_pages_from_list` (in `mm/vmscan.c`, called by zsmalloc/zram) Are the static functions in .c files viable FocusSymbols? Yes, since the guideline specifically mentions inline static functions in headers (.h) and this is .c. Let's check for inlining or if a main symbol exists: * `folio_batch_pageout`: Called in two places within `shrink_folio_list`. * `folio_try_reclaim_free`: Called in `shrink_folio_list` and `folio_batch_pageout` (two callers). * `folio_try_pageout`: Called solely in `folio_batch_pageout`. * `folio_activate_locked`: Called in `shrink_folio_list` and `folio_batch_pageout`. * `folio_try_unmap`: Called once in `shrink_folio_list`. * `shrink_folio_list`: Called in 4 places (`shrink_inactive_list`, `reclaim_folio_list`, `evict_folios`, `reclaim_clean_pages_from_list`). * `reclaim_pages`: Is a direct entry point for `madvise(MADV_PAGEOUT)`. Since `shrink_folio_list` is a very large function, it is unlikely to be inlined and is a good focus symbol. `folio_batch_pageout` and `folio_try_reclaim_free` are also big enough to be symbols, and are directly involved. `reclaim_pages` is an obvious direct entrypoint for `madvise`. `shrink_inactive_list` is the caller during LRU scanning. Therefore, our `FocusSymbols` are:
16/2	2026/11/01 07:37	tool	grepper	0m Args: { "Expression": "vmscan\\.o", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/Makefile=51=obj-y\t\t\t:= filemap.o mempool.o oom_kill.o fadvise.o \\\nmm/Makefile-52-\t\t\t maccess.o page-writeback.o folio-compat.o \\\nmm/Makefile:53:\t\t\t readahead.o folio.o truncate.o vmscan.o shrinker.o \\\nmm/Makefile-54-\t\t\t shmem.o util.o mmzone.o vmstat.o backing-dev.o \\\n" }
17/2	2026/11/01 07:37	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24091 output: 26 thoughts: 479 Thoughts: Analyzing the Dependencies of `vmscan.o` in the Linux Kernel Okay, so `vmscan.o` is definitely built-in, as it's under `obj-y`. No surprises there. But I need to understand its dependencies, especially considering swap and memory control groups (MEMCG). I need to figure out if disabling swap would affect anything in `mm/vmscan.c`. First thought: `folio_batch_pageout` handles the actual pageout operations, writing dirty folios and swapback. Since syzkaller kernels typically have CONFIG_SWAP enabled, I have to check if either `folio_batch_pageout` or `shrink_folio_list` actually require it. But hold on, even if swap is disabled, pageout should still function for file-backed pages. Right? Then I got to this block in `shrink_folio_list`: if the folio is dirty, then depending on whether it's file-lru, it either just continues if it's DMA-pinned or `sc->may_writepage` is false, or queues it for pageout. Specifically, it looks like for dirty swap-backed (anonymous) folios and dirty file-backed folios when `sc->may_writepage` is true, the folio is queued into `pageout_folios`. So, what exactly enables SWAP? A quick check should confirm CONFIG_SWAP. But the crucial question is, is CONFIG_SWAP actually required for the compilation of `vmscan.c`? Since `vmscan.o` is always built in, it shouldn't be. Let's dig deeper in Kconfig.
18/2	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "config SWAP", "PathPrefixes": [ "mm/" ] } Results: { "Output": "mm/Kconfig=9=config ARCH_NO_SWAP\n--\nmm/Kconfig-11-\nmm/Kconfig:12:menuconfig SWAP\nmm/Kconfig-13-\tbool \"Support for paging of anonymous memory (swap)\"\n" }
19/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25027 output: 30 thoughts: 195 Thoughts: Investigating Potential Anonymous Pageout Optimization Okay, so I'm trying to figure out if we even need to explicitly consider `SWAP` operations here, or if there's a more integrated approach for this anonymous pageout situation. The code is structured in a way where `folio_batch_pageout` seems to manage both swap and file writeback. It's a key function to understand. Right, let's just make sure we check this properly before going any further. I need to nail down if the necessary configurations are correctly set to reach the modified code path and, in turn, leverage any optimizations or avoid issues. The instructions are clear: let's go over the Kconfig files and look at the `#ifdef` guards, no assumptions allowed. Importantly, I need to check the "depends on" lines in Kconfig to make sure no parent subsystem configs are needed here. So I'll strip the `CONFIG_` prefix for clarity later. Now, are there any `#ifdef` guards surrounding the key functions I'm interested in, namely `folio_batch_pageout` or even `shrink_folio_list`? That's the real test. Let's dig into `mm/vmscan.c` and focus on the code around lines 1150 to 1850. Hopefully, that will give a clear view.
20/2	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "^#if", "PathPrefixes": [ "mm/vmscan.c" ] } Results: { "Output": "mm/vmscan.c=76=struct scan_control {\n--\nmm/vmscan.c-183-\nmm/vmscan.c:184:#ifdef ARCH_HAS_PREFETCHW\nmm/vmscan.c-185-static inline void prefetchw_prev_lru_folio(struct folio folio,\n--\nmm/vmscan.c=223=static int sc_swappiness(struct scan_control sc, struct mem_cgroup memcg)\n--\nmm/vmscan.c-229-\nmm/vmscan.c:230:#ifdef CONFIG_MEMCG\nmm/vmscan.c-231-\n--\nmm/vmscan.c=260=static bool writeback_throttling_sane(struct scan_control sc)\n--\nmm/vmscan.c-263-\t\treturn true;\nmm/vmscan.c:264:#ifdef CONFIG_CGROUP_WRITEBACK\nmm/vmscan.c-265-\tif (cgroup_subsys_on_dfl(memory_cgrp_subsys))\n--\nmm/vmscan.c=345=static bool can_demote(int nid, struct scan_control sc,\n--\nmm/vmscan.c-364-\nmm/vmscan.c:365:#ifdef CONFIG_SWAP\nmm/vmscan.c-366-static inline bool reclaimable_anon_is_low(struct mem_cgroup memcg,\n--\nmm/vmscan.c=927=enum folio_references {\n--\nmm/vmscan.c-932-\nmm/vmscan.c:933:#ifdef CONFIG_LRU_GEN\nmm/vmscan.c-934-/\n--\nmm/vmscan.c=1458=static unsigned int shrink_folio_list(struct list_head folio_list,\n--\nmm/vmscan.c-1694-\t\t\t\t\tgoto activate_locked;\nmm/vmscan.c:1695:#ifdef CONFIG_TRANSPARENT_HUGEPAGE\nmm/vmscan.c-1696-\t\t\t\tif (nr_pages \u003e= HPAGE_PMD_NR) {\n--\nmm/vmscan.c=2961=static bool can_age_anon_pages(struct lruvec lruvec,\n--\nmm/vmscan.c-2972-\nmm/vmscan.c:2973:#ifdef CONFIG_LRU_GEN\nmm/vmscan.c-2974-\nmm/vmscan.c=2975=DEFINE_STATIC_KEY_FALSE(lru_switch);\nmm/vmscan.c:2976:#ifdef CONFIG_LRU_GEN_ENABLED\nmm/vmscan.c-2977-DEFINE_STATIC_KEY_ARRAY_TRUE(lru_gen_caps, NR_LRU_GEN_CAPS);\n--\nmm/vmscan.c=3025=static struct lruvec get_lruvec(struct mem_cgroup memcg, int nid)\n--\nmm/vmscan.c-3028-\nmm/vmscan.c:3029:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3030-\tif (memcg) {\n--\nmm/vmscan.c=3161=static void reset_bloom_filter(struct lru_gen_mm_state mm_state, unsigned long seq)\n--\nmm/vmscan.c-3180-\nmm/vmscan.c:3181:#ifdef CONFIG_LRU_GEN_WALKS_MMU\nmm/vmscan.c-3182-\nmm/vmscan.c=3183=static struct lru_gen_mm_list get_mm_list(struct mem_cgroup memcg)\n--\nmm/vmscan.c-3189-\nmm/vmscan.c:3190:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3191-\tif (memcg)\n--\nmm/vmscan.c=3223=void lru_gen_add_mm(struct mm_struct mm)\n--\nmm/vmscan.c-3229-\tVM_WARN_ON_ONCE(!list_empty(\u0026mm-\u003elru_gen.list));\nmm/vmscan.c:3230:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3231-\tVM_WARN_ON_ONCE(mm-\u003elru_gen.memcg);\n--\nmm/vmscan.c=3250=void lru_gen_del_mm(struct mm_struct mm)\n--\nmm/vmscan.c-3258-\nmm/vmscan.c:3259:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3260-\tmemcg = mm-\u003elru_gen.memcg;\n--\nmm/vmscan.c-3282-\nmm/vmscan.c:3283:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3284-\tmem_cgroup_put(mm-\u003elru_gen.memcg);\n--\nmm/vmscan.c-3288-\nmm/vmscan.c:3289:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3290-void lru_gen_migrate_mm(struct mm_struct mm)\n--\nmm/vmscan.c=4720=static void lru_gen_rotate_memcg(struct lruvec lruvec, int op)\n--\nmm/vmscan.c-4763-\nmm/vmscan.c:4764:#ifdef CONFIG_MEMCG\nmm/vmscan.c-4765-\n--\nmm/vmscan.c=5981=static int lru_gen_seq_show(struct seq_file m, void v)\n--\nmm/vmscan.c-5994-\nmm/vmscan.c:5995:#ifdef CONFIG_MEMCG\nmm/vmscan.c-5996-\t\tif (memcg)\n--\nmm/vmscan.c=6250=void lru_gen_init_lruvec(struct lruvec lruvec)\n--\nmm/vmscan.c-6269-\nmm/vmscan.c:6270:#ifdef CONFIG_MEMCG\nmm/vmscan.c-6271-\n--\nmm/vmscan.c=7128=unsigned long try_to_free_pages(struct zonelist zonelist, int order,\n--\nmm/vmscan.c-7170-\nmm/vmscan.c:7171:#ifdef CONFIG_MEMCG\nmm/vmscan.c-7172-\n--\nmm/vmscan.c=7956=bool kswapd_test_hopeless(pg_data_t pgdat)\n--\nmm/vmscan.c-7960-\nmm/vmscan.c:7961:#ifdef CONFIG_HIBERNATION\nmm/vmscan.c-7962-/\n--\nmm/vmscan.c=8041=static const struct ctl_table vmscan_sysctl_table[] = {\n--\nmm/vmscan.c-8050-\t},\nmm/vmscan.c:8051:#ifdef CONFIG_NUMA\nmm/vmscan.c-8052-\t{\n--\nmm/vmscan.c=8073=module_init(kswapd_init)\nmm/vmscan.c-8074-\nmm/vmscan.c:8075:#ifdef CONFIG_NUMA\nmm/vmscan.c-8076-/\n--\nmm/vmscan.c=8420=EXPORT_SYMBOL_GPL(check_move_unevictable_folios);\nmm/vmscan.c-8421-\nmm/vmscan.c:8422:#if defined(CONFIG_SYSFS) \u0026\u0026 defined(CONFIG_NUMA)\nmm/vmscan.c-8423-static ssize_t reclaim_store(struct device dev,\n" }
21/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 27549 output: 30 thoughts: 193 Thoughts: Analyzing Swap and Folio Paging Behavior Okay, so I'm looking at these modified functions and I see they're not enclosed in any `#ifdef` blocks, which is a bit of a starting point for figuring out what they're actually going to do. Diving into `shrink_folio_list`, specifically, I'm thinking about swap. I know `CONFIG_SWAP` enables swapping anonymous folios. Without swap enabled, there's no pageout for anon memory, right? It's just...gone. Or rather, it can't be moved to swap, which means that `pageout` for anon pages wouldn't even be called. It would only be called for dirty file folios, and `sc->may_writepage` is frequently zero, making direct reclaim unlikely for file pages. Now, I see that `CONFIG_TRANSPARENT_HUGEPAGE` might have some relevance, especially when dealing with large folio splitting. However, the real question is whether or not `SWAP` is needed or recommended to force the swap pageout behavior, which I suspect is the core of what's happening. I need to confirm this: I'm convinced `CONFIG_SWAP` is essential for properly exercising the pageout behavior for dirty anonymous pages. Without it, that key behavior, the pageout of dirty anonymous pages, simply won't happen. The system will be missing a major portion of its intended behavior. To confirm this, I should probably go directly to `mm/vmscan.c` to check out how `pageout` is implemented. That's the best next step to fully understand the logic here.
22/2	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "pageout\\(", "PathPrefixes": [ "mm/vmscan.c" ] } Results: { "Output": "mm/vmscan.c=657=void __acct_reclaim_writeback(pg_data_t pgdat, struct folio folio,\n--\nmm/vmscan.c-677-\nmm/vmscan.c:678:/* possible outcome of pageout() /\nmm/vmscan.c-679-typedef enum {\n--\nmm/vmscan.c-692- /\nmm/vmscan.c:693:static pageout_t pageout(struct swap_io_ctx ctx, struct address_space mapping,\nmm/vmscan.c-694-\t\tstruct folio folio, struct list_head folio_list)\n--\nmm/vmscan.c=1280=enum folio_pageout_result {\n--\nmm/vmscan.c-1291- /\nmm/vmscan.c:1292:static enum folio_pageout_result folio_try_pageout(struct folio folio,\nmm/vmscan.c-1293-\t\tstruct scan_control sc, struct swap_io_ctx ctx,\n--\nmm/vmscan.c-1298-\nmm/vmscan.c:1299:\tswitch (pageout(ctx, mapping, folio, folio_list)) {\nmm/vmscan.c-1300-\tcase PAGE_ACTIVATE:\n--\nmm/vmscan.c-1336-\nmm/vmscan.c:1337:static void folio_batch_pageout(struct folio_batch batch,\nmm/vmscan.c-1338-\t\tstruct reclaim_folio_state state, struct scan_control sc,\n--\nmm/vmscan.c-1393-\nmm/vmscan.c:1394:\t\tswitch (folio_try_pageout(folio, sc, ctx, folio_list)) {\nmm/vmscan.c-1395-\t\tcase FOLIO_PAGEOUT_ACTIVATE:\n--\nmm/vmscan.c=1458=static unsigned int shrink_folio_list(struct list_head folio_list,\n--\nmm/vmscan.c-1772-\t\t\t * recheck that this necessitates is documented in\nmm/vmscan.c:1773:\t\t\t * folio_batch_pageout().\nmm/vmscan.c-1774-\t\t\t */\n--\nmm/vmscan.c-1776-\t\t\tif (!folio_batch_add(\u0026pageout_folios, folio))\nmm/vmscan.c:1777:\t\t\t\tfolio_batch_pageout(\u0026pageout_folios, \u0026state,\nmm/vmscan.c-1778-\t\t\t\t\t\t sc, stat, \u0026ctx, folio_list);\n--\nmm/vmscan.c-1807-\tif (folio_batch_count(\u0026pageout_folios)) {\nmm/vmscan.c:1808:\t\tfolio_batch_pageout(\u0026pageout_folios, \u0026state, sc, stat,\nmm/vmscan.c-1809-\t\t\t\t \u0026ctx, folio_list);\n" }
23/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 28880 output: 34 thoughts: 20 Thoughts: Here's my take on the thought process: Diving into `vmscan.c` to Understand `pageout()` Okay, so I need to understand what's going on with this `pageout()` function. Since it's central to memory management, I'll start by taking a look at the definition itself and the surrounding lines of code within `mm/vmscan.c`. I expect this area to be dense, but the context around the function definition will be crucial for understanding its role in the virtual memory scanning process and how it handles page eviction. I'm hoping to get a quick grasp of its basic behavior and identify any key data structures or interactions that immediately jump out as important. Time to get my hands dirty.
24/2	2026/11/01 07:38	tool	read-file	0m Args: { "File": "mm/vmscan.c", "FirstLine": 690, "LineCount": 45 } Results: { "Contents": " 690:\t/\n 691:\t pageout is called by shrink_folio_list() for each dirty folio.\n 692:\t /\n 693:\tstatic pageout_t pageout(struct swap_io_ctx ctx, struct address_space mapping,\n 694:\t\t\tstruct folio folio, struct list_head folio_list)\n 695:\t{\n 696:\t\tint res;\n 697:\t\n 698:\t\t/\n 699:\t\t * We no longer attempt to writeback filesystem folios here, other\n 700:\t\t * than tmpfs/shmem. That's taken care of in page-writeback.\n 701:\t\t * If we find a dirty filesystem folio at the end of the LRU list,\n 702:\t\t * typically that means the filesystem is saturating the storage\n 703:\t\t * with contiguous writes and telling it to write a folio here\n 704:\t\t * would only make the situation worse by injecting an element\n 705:\t\t * of random access.\n 706:\t\t \n 707:\t\t If the folio is swapcache, write it back even if that would\n 708:\t\t * block, for some throttling. This happens by accident, because\n 709:\t\t * swap_backing_dev_info is bust: it doesn't reflect the\n 710:\t\t * congestion state of the swapdevs. Easy to fix, if needed.\n 711:\t\t \n 712:\t\t A freeable shmem or swapcache folio is referenced only by the\n 713:\t\t * caller that isolated the folio and the page cache.\n 714:\t\t /\n 715:\t\tif (folio_ref_count(folio) != 1 + folio_nr_pages(folio) \|\| !mapping)\n 716:\t\t\treturn PAGE_KEEP;\n 717:\t\tif (!shmem_mapping(mapping) \u0026\u0026 !folio_test_anon(folio))\n 718:\t\t\treturn PAGE_ACTIVATE;\n 719:\t\tif (!folio_clear_dirty_for_io(folio))\n 720:\t\t\treturn PAGE_CLEAN;\n 721:\t\n 722:\t\tfolio_set_reclaim(folio);\n 723:\t\n 724:\t\t/\n 725:\t\t * The large shmem folio can be split if CONFIG_THP_SWAP is not enabled\n 726:\t\t * or we failed to allocate contiguous swap entries, in which case\n 727:\t\t * the split out folios get added back to folio_list.\n 728:\t\t */\n 729:\t\tif (shmem_mapping(mapping))\n 730:\t\t\tres = shmem_writeout(ctx, folio, folio_list);\n 731:\t\telse\n 732:\t\t\tres = swap_writeout(ctx, folio);\n 733:\t\n 734:\t\tif (res \u003c 0)\n" }
25/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 29840 output: 28 thoughts: 210 Thoughts: Analyzing Pageout Behavior: The Anonymous Memory Puzzle Okay, let's dive into this pageout logic. Looking specifically at lines 717-718 and then 729-732, it seems pretty clear that the `pageout` function is designed to handle either shared memory (`shmem`) or swapped pages. The conditional branching explicitly checks for `shmem_mapping` and then dispatches to `shmem_writeout` or `swap_writeout` accordingly. The implication is, that if neither shared memory nor swap is involved, there's no writeout action for anonymous memory. Effectively, if we disable swap and shared memory, anonymous memory pageout is dormant. This raises some important configuration considerations. We need to verify the values of `CONFIG_SWAP` and `CONFIG_SHMEM`. The question is how pageout behaves. I also need to check `CONFIG_TRANSPARENT_HUGEPAGE` – it could interact here too, potentially influencing memory management behavior. To get a more complete picture, let's explore `SWAP` in Kconfig to see the dependencies. I have to verify if `SWAP` depends on other configuration options.
26/2	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "config SWAP", "PathPrefixes": [ "mm/Kconfig" ] } Results: { "Output": "mm/Kconfig=9=config ARCH_NO_SWAP\n--\nmm/Kconfig-11-\nmm/Kconfig:12:menuconfig SWAP\nmm/Kconfig-13-\tbool \"Support for paging of anonymous memory (swap)\"\n" }
27/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 30404 output: 31 thoughts: 16 Thoughts: Okay, here's my interpretation of reading those lines of a Kconfig file, framed in a first-person perspective, assuming I'm already well-versed in kernel configuration: Diving into the Kconfig: mm/Kconfig - Lines 10-30 Alright, let's pull up the `mm/Kconfig` file and zero in on lines 10 through 30. Hmm, let's see what's being defined in this section. I'm expecting this area to cover memory management options – possibly related to memory zones, page allocation, or perhaps some low-level NUMA settings. Given the context of `mm/`, it's almost certainly related to the core memory management subsystem. I'm hoping to get a quick overview here to see if there are any new or changed options since I last reviewed this. I'll be looking for things like: * Choice Blocks: Are there any choices being presented for memory management strategy? I'd be interested to see if there are newer alternatives to existing algorithms. * Dependency Checking: I'll look for `depends on` statements to see how these options are linked to other kernel features. This will show me where the enabling conditions are. This is a very important part of my work, to find what the enabling conditions are for this code to be included. * Default Values: What are the default values being set for these variables? This often gives a clue as to the kernel developers' intended usage or the "safe" setting for most scenarios. * Help Text: I'll quickly skim the `help` text to get a sense of the intended functionality and potential impact of any newly introduced options. Is it an important feature, or something niche? * Visibility: I want to get a sense of how these options will be presented to the user. Are these expert-level configurations that will show up only if you select a particular option, or are they top-level features? I'm ready to digest that Kconfig information!
28/2	2026/11/01 07:38	tool	read-file	0m Args: { "File": "mm/Kconfig", "FirstLine": 10, "LineCount": 25 } Results: { "Contents": " 10:\t\tbool\n 11:\t\n 12:\tmenuconfig SWAP\n 13:\t\tbool \"Support for paging of anonymous memory (swap)\"\n 14:\t\tdepends on MMU \u0026\u0026 BLOCK \u0026\u0026 !ARCH_NO_SWAP\n 15:\t\tdefault y\n 16:\t\thelp\n 17:\t\t This option allows you to choose whether you want to have support\n 18:\t\t for so called swap devices or swap files in your kernel that are\n 19:\t\t used to provide more virtual memory than the actual RAM present\n 20:\t\t in your computer. If unsure say Y.\n 21:\t\n 22:\tconfig ZSWAP\n 23:\t\tbool \"Compressed cache for swap pages\"\n 24:\t\tdepends on SWAP\n 25:\t\tselect CRYPTO\n 26:\t\tselect ZSMALLOC\n 27:\t\thelp\n 28:\t\t A lightweight compressed cache for swap pages. It takes\n 29:\t\t pages that are in the process of being swapped out and attempts to\n 30:\t\t compress them into a dynamically allocated RAM-based memory pool.\n 31:\t\t This can result in a significant I/O reduction on swap device and,\n 32:\t\t in the case where decompressing from RAM is faster than swap device\n 33:\t\t reads, can also improve workload performance.\n 34:\t\n" }
29/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 31236 output: 28 thoughts: 42 Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience: Kernel Configuration Dependencies: SWAP, MMU, and Shared Memory Right, so I'm thinking about the `SWAP` feature. It's pretty straightforward: its functionality is inherently tied to the Memory Management Unit, or `MMU`, and the `BLOCK` layer. That makes sense, you know, paging to and from block devices. The `!ARCH_NO_SWAP` condition is obviously a given - we need to ensure the architecture actually allows for swapping. No surprises there. But now my mind drifts to `SHMEM`... shared memory. I'm wondering if there's any direct dependency or implication regarding `SWAP`. It's worth double-checking the configuration. Let me quickly examine `config SHMEM`... just to make sure I haven't missed a potential interaction in the kernel's memory management landscape. It's always good to be thorough, especially when dealing with such fundamental aspects of system resource allocation. Time for a quick look.
30/2	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "config SHMEM", "PathPrefixes": [ "init/Kconfig" ] } Results: { "Output": "init/Kconfig=1739=config EVENTFD\n--\ninit/Kconfig-1747-\ninit/Kconfig:1748:config SHMEM\ninit/Kconfig-1749-\tbool \"Use full shmem filesystem\" if EXPERT\n" }
31/2	2026/11/01 07:38	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 31610 output: 275 thoughts: 1219 Thoughts: Focus Symbol Selection for Pageout Batching Okay, so `SWAP` is definitely relevant to this. I need to figure out the right `FocusSymbols` for fuzzing this new batch pageout functionality. First, let's list the functions involved in this diff: `shrink_folio_list` (the modified orchestrator), `folio_batch_pageout` (the core batch pageout function), `folio_try_reclaim_free`, `folio_try_pageout`, `folio_activate_locked`, `folio_try_unmap`, and `reclaim_pages` (the `madvise(..., MADV_PAGEOUT)` entrypoint). Now, let's be strategic and not list ubiquitous functions. So I have to carefully consider the applicability of each proposed focus symbol. Are any of these generically called by nearly every program? No. These functions are specific to page reclaim and the new batch pageout mechanism, triggered under memory pressure, cgroup reclaim, or direct user space control. I need to quickly eliminate any potential for inlining. `folio_try_unmap` and `folio_try_pageout` are static and called only once (within `shrink_folio_list` and `folio_batch_pageout` respectively), so they might be inlined. But `folio_batch_pageout` is called twice from `shrink_folio_list`. The other functions are all called within the key functions. `shrink_folio_list` is definitely not inlined. Great. Given this, I believe my focus symbols should be: `shrink_folio_list`, `folio_batch_pageout`, `folio_try_reclaim_free`, `folio_try_pageout`, `folio_activate_locked`, `folio_try_unmap`, and `reclaim_pages`. To confirm the wisdom of this, I need to verify that this is truly worth fuzzing. Yes, absolutely. This is core memory management in `mm/vmscan.c`. There's major refactoring here, with dirty folios now being batched and pageout locks being released and reacquired, creating new concurrency challenges. Plus, there are new runtime assertions being added. This is exactly the kind of change that needs focused fuzzing. Finally, this functionality is directly reachable via syscalls such as `madvise(..., MADV_PAGEOUT)`, cgroup memory reclaim, and memory pressure. So, let's summarize: * `WorthFuzzing`: True * `EnableConfigs`: `SWAP` and `SHMEM` * `FocusSymbols`: `shrink_folio_list`, `folio_batch_pageout`, `folio_try_reclaim_free`, `folio_try_pageout`, `folio_activate_locked`, `folio_try_unmap`, `reclaim_pages` * `Reasoning`: Major refactoring of pageout, introduction of batching, new concurrency windows, directly reachable through userspace. Alright, I am ready to invoke `set-results`.
32/2	2026/11/01 07:38	tool	set-results	0m Args: { "EnableConfigs": [ "SWAP", "SHMEM" ], "FocusSymbols": [ "shrink_folio_list", "folio_batch_pageout", "folio_try_reclaim_free", "folio_try_pageout", "folio_activate_locked", "folio_try_unmap", "reclaim_pages" ], "Reasoning": "The patch modifies core memory management code in mm/vmscan.c, fundamentally changing how dirty folios are handled during page reclaim in shrink_folio_list(). Instead of holding folio locks during pageout, dirty folios are now unlocked, batched in pageout_folios, and processed asynchronously in the newly added folio_batch_pageout(). This introduces an unlocked window where folios can be concurrently modified, remapped, or DMA pinned, necessitating lock re-acquisition and revalidation checks. The patch also adds several VM_WARN_ON runtime assertions and refactors reclaim helpers (folio_try_reclaim_free, folio_activate_locked, folio_try_unmap). These paths are reachable via memory pressure or syscalls such as madvise(MADV_PAGEOUT) and cgroup reclaim, making this highly worthy of fuzzing.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "SWAP", "SHMEM" ], "FocusSymbols": [ "shrink_folio_list", "folio_batch_pageout", "folio_try_reclaim_free", "folio_try_pageout", "folio_activate_locked", "folio_try_unmap", "reclaim_pages" ], "Reasoning": "The patch modifies core memory management code in mm/vmscan.c, fundamentally changing how dirty folios are handled during page reclaim in shrink_folio_list(). Instead of holding folio locks during pageout, dirty folios are now unlocked, batched in pageout_folios, and processed asynchronously in the newly added folio_batch_pageout(). This introduces an unlocked window where folios can be concurrently modified, remapped, or DMA pinned, necessitating lock re-acquisition and revalidation checks. The patch also adds several VM_WARN_ON runtime assertions and refactors reclaim helpers (folio_try_reclaim_free, folio_activate_locked, folio_try_unmap). These paths are reachable via memory pressure or syscalls such as madvise(MADV_PAGEOUT) and cgroup reclaim, making this highly worthy of fuzzing.", "WorthFuzzing": true }
33/1	2026/11/01 07:38	action	If	0m Args: { "WorthFuzzing": true } Results: null
34/2	2026/11/01 07:38	agent	kmsan-evaluator	0m Model: core Args: null Results: { "KMSANReasoning": "The patch refactors pageout and reclamation logic in mm/vmscan.c by batching dirty folio writebacks and modularizing helpers (folio_batch_pageout, folio_try_reclaim_free, folio_try_pageout, folio_activate_locked, folio_try_unmap).\n\nAll newly introduced stack structures and batches (such as struct reclaim_folio_state and pageout_folios) are explicitly zero-initialized and initialized with folio_batch_init() and INIT_LIST_HEAD(). The code does not expose any uninitialized variables, conditional branches on uninitialized state, or data copies to user space (info-leaks).\n\nThe potential risks introduced by this change are memory management logic errors, reference counting inconsistencies, race conditions from unlocking and re-locking folios, or use-after-free conditions. These classes of bugs are thoroughly covered by KASAN, LOCKDEP, and internal VM asserts (VM_WARN_ON/VM_BUG_ON). Because there are no uninitialized memory risks that KMSAN specifically detects, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Instruction: You are an expert Linux kernel security engineer specializing in kernel memory error detectors (KASAN and KMSAN). Your job is to review the provided patch series and determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer) fuzzing session in addition to standard KASAN fuzzing. CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN: - Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable a comprehensive suite of debugging tools and sanitizers, including KASAN (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks. - KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap, or page allocations) and kernel-to-user memory info-leaks. Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN, LOCKDEP, OR OTHER STANDARD BUG DETECTORS. A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks that are detected ONLY by KMSAN. Look holistically at the patch series and surrounding code. Even if no direct uninitialized field accesses or new buffer allocations are added in the diff itself, a patch may alter control flow, bounds checking, or data length calculations in ways that change how the rest of the code operates on existing buffers (e.g. allowing uninitialized stack/heap memory to be read, copied to user space, or used in control flow). Do not hesitate to use your code access tools to inspect the surrounding code, called functions, and callers. Set NeedsKMSAN=true ONLY IF the patch introduces or modifies: 1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb attributes, ioctl output arguments, socket options, or BPF buffers) where fields or structure padding might not be fully initialized/zeroed. 2. Conditional logic or branching that depends on potentially uninitialized variables or struct fields. 3. Allocation or initialization of complex data structures where uninitialized fields could be read later in reachable code paths. 4. Bounds checks, lengths, or logic in a way that allows surrounding code to access uninitialized bytes of existing buffers. Set NeedsKMSAN=false IF: - The code changes primarily risk out-of-bounds access, array overflows, NULL pointer dereferences, locking deadlocks, or use-after-free bugs (these are already caught by KASAN, LOCKDEP, or standard bug detectors). - All stack/heap structures touched or introduced by the patch are fully zeroed or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied. - The patch does not introduce any risk of uninitialized memory usage or info-leaks. Use your code access tools to inspect the surrounding code if necessary, then provide detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch. 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. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 1d1e051d34c43d5fa528570ffc4e6bd0d73e3e6c Author: syz-cluster <triage@syzkaller.com> Date: Sun Nov 1 07:36:48 2026 +0000 syz-cluster: applied patch under review diff --git a/mm/vmscan.c b/mm/vmscan.c index fb9f8f020f6342..1150361e7d5254 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1155,23 +1155,322 @@ static bool may_enter_fs(struct folio folio, gfp_t gfp_mask) return false; } +/ Activate an isolated, locked folio and account the activation. / +static void folio_activate_locked(struct folio folio, + struct reclaim_stat stat) +{ + unsigned int nr_pages = folio_nr_pages(folio); + + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); + VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio); + + / Not a candidate for swapping, so reclaim swap space. / + if (folio_test_swapcache(folio) && + (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio))) + folio_free_swap(folio); + if (!folio_test_mlocked(folio)) { + int type = folio_is_file_lru(folio); + + folio_set_active(folio); + stat->nr_activate[type] += nr_pages; + count_memcg_folio_events(folio, PGACTIVATE, nr_pages); + } +} + +/ Results accumulated across a shrink_folio_list() invocation. / +struct reclaim_folio_state { + struct list_head ret_folios; + struct folio_batch free_folios; + unsigned int nr_reclaimed; +}; + +enum folio_reclaim_result { + FOLIO_RECLAIM_KEEP, + FOLIO_RECLAIM_ACTIVATE, + FOLIO_RECLAIM_DONE, +}; + +/ + * Called with the folio locked. KEEP and ACTIVATE leave it locked and + * owned by the caller. DONE consumes the caller's reference; the caller + * must not access the folio again, even if freeing is deferred. + / +static enum folio_reclaim_result folio_try_reclaim_free(struct folio folio, + struct reclaim_folio_state state, + struct scan_control sc) +{ + const unsigned int nr_pages = folio_nr_pages(folio); + struct address_space mapping = folio_mapping(folio); + + / + * If the folio has buffers, try to free the buffer mappings + * associated with this folio. If we succeed we try to free + * the folio as well. + * + * We do this even if the folio is dirty. + * filemap_release_folio() does not perform I/O, but it is + * possible for a folio to have the dirty flag set, but it + * is actually clean (all its buffers are clean). This + * happens if the buffers were written out directly, with + * bh_submit(). ext3 will do this, as well as the blockdev + * mapping. filemap_release_folio() will discover that + * cleanness and will drop the buffers and mark the folio + * clean - it can be freed. + * + * Rarely, folios can have buffers and no ->mapping. These + * are the folios which were not successfully invalidated in + * truncate_cleanup_folio(). We try to drop those buffers + * here and if that worked, and the folio is no longer + * mapped into process address space (refcount == 1) it can + * be freed. Otherwise, leave the folio on the LRU so it is + * swappable. + / + if (folio_needs_release(folio)) { + if (!filemap_release_folio(folio, sc->gfp_mask)) + return FOLIO_RECLAIM_ACTIVATE; + + if (!mapping && folio_ref_count(folio) == 1) { + folio_unlock(folio); + if (folio_put_testzero(folio)) + goto free_it; + + / + * Rare race with speculative reference. The + * speculative reference will free this folio + * shortly, so we may increment nr_reclaimed here + * and leave it off the LRU. + / + state->nr_reclaimed += nr_pages; + return FOLIO_RECLAIM_DONE; + } + } + + if (folio_test_lazyfree(folio)) { + / follow __remove_mapping for reference / + if (!folio_ref_freeze(folio, 1)) + return FOLIO_RECLAIM_KEEP; + / + * The folio has only one reference left, which is + * from the isolation. After the caller puts the + * folio back on the lru and drops the reference, the + * folio will be freed anyway. It doesn't matter + * which lru it goes on. So we don't bother checking + * the dirty flag here. + / + count_vm_events(PGLAZYFREED, nr_pages); + count_memcg_folio_events(folio, PGLAZYFREED, nr_pages); + } else if (!mapping \|\| !__remove_mapping(mapping, folio, true, + sc->target_mem_cgroup)) + return FOLIO_RECLAIM_KEEP; + + folio_unlock(folio); +free_it: + VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio); + state->nr_reclaimed += nr_pages; + + folio_unqueue_deferred_split(folio); + if (folio_batch_add(&state->free_folios, folio) == 0) { + mem_cgroup_uncharge_folios(&state->free_folios); + try_to_unmap_flush(); + free_unref_folios(&state->free_folios); + } + return FOLIO_RECLAIM_DONE; +} + +enum folio_pageout_result { + FOLIO_PAGEOUT_KEEP_LOCKED, + FOLIO_PAGEOUT_KEEP_UNLOCKED, + FOLIO_PAGEOUT_ACTIVATE, + FOLIO_PAGEOUT_RECLAIM, / folio is locked, hand it to folio_try_reclaim_free() / +}; + / - * shrink_folio_list() returns the number of reclaimed pages + * Called with the folio locked. All results leave it locked except + * KEEP_UNLOCKED. The caller retains ownership in every case; RECLAIM + * only allows a subsequent reclaim attempt, it does not free the folio. + / +static enum folio_pageout_result folio_try_pageout(struct folio folio, + struct scan_control sc, struct swap_io_ctx ctx, + struct list_head folio_list) +{ + struct address_space const mapping = folio_mapping(folio); + const unsigned int nr_pages = folio_nr_pages(folio); + + switch (pageout(ctx, mapping, folio, folio_list)) { + case PAGE_ACTIVATE: + /* + * If shmem folio is split when writeback to swap, the + * tail pages will make their own pass through this + * function and be accounted then. There is no need to + * clamp nr_pages here: folio_activate_locked() derives + * the count from folio_nr_pages() itself. + / + if (nr_pages > 1 && !folio_test_large(folio)) + sc->nr_scanned -= (nr_pages - 1); + return FOLIO_PAGEOUT_ACTIVATE; + case PAGE_KEEP: + return FOLIO_PAGEOUT_KEEP_LOCKED; + case PAGE_SUCCESS: + if (nr_pages > 1 && !folio_test_large(folio)) + sc->nr_scanned -= (nr_pages - 1); + + if (folio_test_writeback(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + if (folio_test_dirty(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + + / + * A synchronous write - probably a ramdisk. Go ahead + * and try to reclaim the folio. + / + if (!folio_trylock(folio)) + return FOLIO_PAGEOUT_KEEP_UNLOCKED; + if (folio_test_dirty(folio) \|\| folio_test_writeback(folio)) + return FOLIO_PAGEOUT_KEEP_LOCKED; + fallthrough; + case PAGE_CLEAN: + return FOLIO_PAGEOUT_RECLAIM; + } + unreachable(); +} + +static void folio_batch_pageout(struct folio_batch batch, + struct reclaim_folio_state state, struct scan_control sc, + struct reclaim_stat stat, struct swap_io_ctx ctx, + struct list_head folio_list) +{ + unsigned int nr = folio_batch_count(batch); + unsigned int i; + + / + * Reuse this private batch to collect the locked folios. Reinit + * leaves the array intact; nr preserves the original input count. + * Adding each accepted folio writes at or before the current read + * index, so entries we have not read yet cannot be overwritten. + / + folio_batch_reinit(batch); + + / + * Revalidate after taking the lock: writeback may have started, or + * a swap fault may have remapped the folio and allowed GUP to pin it. + * Keeping an unmapped folio locked prevents swap faults from mapping + * it again before the TLB flush and pageout. The lock alone does not + * exclude GUP, so existing mappings and pins must both be checked. + / + for (i = 0; i < nr; i++) { + struct folio folio = batch->folios[i]; + + if (!folio_trylock(folio)) { + list_add(&folio->lru, &state->ret_folios); + continue; + } + + VM_WARN_ON_FOLIO(folio_test_lru(folio), folio); + + /* The folio may have changed while it was unlocked. / + if (folio_test_writeback(folio) \|\| folio_mapped(folio) \|\| + folio_maybe_dma_pinned(folio)) { + folio_unlock(folio); + list_add(&folio->lru, &state->ret_folios); + continue; + } + + folio_batch_add(batch, folio); + } + nr = folio_batch_count(batch); + + if (!nr) + return; + + / + * Flush writable TLB entries before any folio in the batch is + * submitted for I/O. + / + try_to_unmap_flush_dirty(); + + for (i = 0; i < nr; i++) { + struct folio folio = batch->folios[i]; + + switch (folio_try_pageout(folio, sc, ctx, folio_list)) { + case FOLIO_PAGEOUT_ACTIVATE: + goto activate_locked; + case FOLIO_PAGEOUT_KEEP_LOCKED: + goto keep_locked; + case FOLIO_PAGEOUT_KEEP_UNLOCKED: + goto keep; + case FOLIO_PAGEOUT_RECLAIM: + break; /* folio is locked; try to free it below / + } + + switch (folio_try_reclaim_free(folio, state, sc)) { + case FOLIO_RECLAIM_ACTIVATE: + goto activate_locked; + case FOLIO_RECLAIM_KEEP: + goto keep_locked; + case FOLIO_RECLAIM_DONE: + continue; + } +activate_locked: + folio_activate_locked(folio, stat); +keep_locked: + folio_unlock(folio); +keep: + list_add(&folio->lru, &state->ret_folios); + } + folio_batch_reinit(batch); +} + +static bool folio_try_unmap(struct folio folio, struct reclaim_stat stat, + unsigned int nr_pages) +{ + enum ttu_flags flags = TTU_BATCH_FLUSH; + const bool was_swapbacked = folio_test_swapbacked(folio); + + if (folio_test_pmd_mappable(folio)) + flags \|= TTU_SPLIT_HUGE_PMD; + / + * Without TTU_SYNC, try_to_unmap will only begin to hold PTL + * from the first present PTE within a large folio. Some + * initial PTEs might be skipped due to races with parallel + * PTE writes in which PTEs can be cleared temporarily before + * being written new present values. This will lead to a large + * folio is still mapped while some subpages have been + * partially unmapped after try_to_unmap; TTU_SYNC helps + * try_to_unmap acquire PTL from the first PTE, eliminating the + * influence of temporary PTE values. + / + if (folio_test_large(folio)) + flags \|= TTU_SYNC; + + try_to_unmap(folio, flags); + if (folio_mapped(folio)) { + stat->nr_unmap_fail += nr_pages; + if (!was_swapbacked && folio_test_swapbacked(folio)) + stat->nr_lazyfree_fail += nr_pages; + return false; + } + return true; +} + +/ + * Reclaimed folios are counted in the return value. / static unsigned int shrink_folio_list(struct list_head folio_list, struct pglist_data pgdat, struct scan_control sc, struct reclaim_stat stat, bool ignore_references, struct mem_cgroup memcg) { - struct folio_batch free_folios; - LIST_HEAD(ret_folios); + struct reclaim_folio_state state = {}; + struct folio_batch pageout_folios; LIST_HEAD(demote_folios); - unsigned int nr_reclaimed = 0, nr_demoted = 0; + unsigned int nr_demoted = 0; unsigned int pgactivate = 0; bool do_demote_pass; struct swap_io_ctx ctx = {}; - folio_batch_init(&free_folios); + INIT_LIST_HEAD(&state.ret_folios); + folio_batch_init(&state.free_folios); + folio_batch_init(&pageout_folios); memset(stat, 0, sizeof(stat)); cond_resched(); do_demote_pass = can_demote(pgdat->node_id, sc, memcg); @@ -1433,36 +1732,9 @@ static unsigned int shrink_folio_list(struct list_head folio_list, * The folio is mapped into the page tables of one or more * processes. Try to unmap it here. / - if (folio_mapped(folio)) { - enum ttu_flags flags = TTU_BATCH_FLUSH; - bool was_swapbacked = folio_test_swapbacked(folio); - - if (folio_test_pmd_mappable(folio)) - flags \|= TTU_SPLIT_HUGE_PMD; - / - * Without TTU_SYNC, try_to_unmap will only begin to - * hold PTL from the first present PTE within a large - * folio. Some initial PTEs might be skipped due to - * races with parallel PTE writes in which PTEs can be - * cleared temporarily before being written new present - * values. This will lead to a large folio is still - * mapped while some subpages have been partially - * unmapped after try_to_unmap; TTU_SYNC helps - * try_to_unmap acquire PTL from the first PTE, - * eliminating the influence of temporary PTE values. - / - if (folio_test_large(folio)) - flags \|= TTU_SYNC; - - try_to_unmap(folio, flags); - if (folio_mapped(folio)) { - stat->nr_unmap_fail += nr_pages; - if (!was_swapbacked && - folio_test_swapbacked(folio)) - stat->nr_lazyfree_fail += nr_pages; - goto activate_locked; - } - } + if (folio_mapped(folio) && + !folio_try_unmap(folio, stat, nr_pages)) + goto activate_locked; / * Folio is unmapped now so it cannot be newly pinned anymore. @@ -1474,7 +1746,6 @@ static unsigned int shrink_folio_list(struct list_head folio_list, if (folio_maybe_dma_pinned(folio)) goto activate_locked; - mapping = folio_mapping(folio); if (folio_test_dirty(folio)) { if (folio_is_file_lru(folio)) { / @@ -1495,164 +1766,53 @@ static unsigned int shrink_folio_list(struct list_head folio_list, goto keep_locked; if (!sc->may_writepage) goto keep_locked; - / - * Folio is dirty. Flush the TLB if a writable entry - * potentially exists to avoid CPU writes after I/O - * starts and then write it out here. + * Drop the lock so swap faults finding this folio + * via swap cache lookup can make progress; the + * recheck that this necessitates is documented in + * folio_batch_pageout(). / - try_to_unmap_flush_dirty(); - switch (pageout(&ctx, mapping, folio, folio_list)) { - case PAGE_KEEP: - goto keep_locked; - case PAGE_ACTIVATE: - / - * If shmem folio is split when writeback to swap, - * the tail pages will make their own pass through - * this function and be accounted then. - / - if (nr_pages > 1 && !folio_test_large(folio)) { - sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } - goto activate_locked; - case PAGE_SUCCESS: - if (nr_pages > 1 && !folio_test_large(folio)) { - sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } - if (folio_test_writeback(folio)) - goto keep; - if (folio_test_dirty(folio)) - goto keep; - - / - * A synchronous write - probably a ramdisk. Go - * ahead and try to reclaim the folio. - / - if (!folio_trylock(folio)) - goto keep; - if (folio_test_dirty(folio) \|\| - folio_test_writeback(folio)) - goto keep_locked; - mapping = folio_mapping(folio); - fallthrough; - case PAGE_CLEAN: - ; / try to free the folio below / - } - } - - / - * If the folio has buffers, try to free the buffer - * mappings associated with this folio. If we succeed - * we try to free the folio as well. - * - * We do this even if the folio is dirty. - * filemap_release_folio() does not perform I/O, but it - * is possible for a folio to have the dirty flag set, - * but it is actually clean (all its buffers are clean). - * This happens if the buffers were written out directly, - * with bh_submit(). ext3 will do this, as well as - * the blockdev mapping. filemap_release_folio() will - * discover that cleanness and will drop the buffers - * and mark the folio clean - it can be freed. - * - * Rarely, folios can have buffers and no ->mapping. - * These are the folios which were not successfully - * invalidated in truncate_cleanup_folio(). We try to - * drop those buffers here and if that worked, and the - * folio is no longer mapped into process address space - * (refcount == 1) it can be freed. Otherwise, leave - * the folio on the LRU so it is swappable. - / - if (folio_needs_release(folio)) { - if (!filemap_release_folio(folio, sc->gfp_mask)) - goto activate_locked; - if (!mapping && folio_ref_count(folio) == 1) { - folio_unlock(folio); - if (folio_put_testzero(folio)) - goto free_it; - else { - / - * rare race with speculative reference. - * the speculative reference will free - * this folio shortly, so we may - * increment nr_reclaimed here (and - * leave it off the LRU). - / - nr_reclaimed += nr_pages; - continue; - } - } + folio_unlock(folio); + if (!folio_batch_add(&pageout_folios, folio)) + folio_batch_pageout(&pageout_folios, &state, + sc, stat, &ctx, folio_list); + continue; } - if (folio_test_lazyfree(folio)) { - / follow __remove_mapping for reference / - if (!folio_ref_freeze(folio, 1)) - goto keep_locked; - / - * The folio has only one reference left, which is - * from the isolation. After the caller puts the - * folio back on the lru and drops the reference, the - * folio will be freed anyway. It doesn't matter - * which lru it goes on. So we don't bother checking - * the dirty flag here. - / - count_vm_events(PGLAZYFREED, nr_pages); - count_memcg_folio_events(folio, PGLAZYFREED, nr_pages); - } else if (!mapping \|\| !__remove_mapping(mapping, folio, true, - sc->target_mem_cgroup)) + switch (folio_try_reclaim_free(folio, &state, sc)) { + case FOLIO_RECLAIM_ACTIVATE: + goto activate_locked; + case FOLIO_RECLAIM_KEEP: goto keep_locked; - - folio_unlock(folio); -free_it: - / - * Folio may get swapped out as a whole, need to account - * all pages in it. - / - nr_reclaimed += nr_pages; - - folio_unqueue_deferred_split(folio); - if (folio_batch_add(&free_folios, folio) == 0) { - mem_cgroup_uncharge_folios(&free_folios); - try_to_unmap_flush(); - free_unref_folios(&free_folios); + case FOLIO_RECLAIM_DONE: + continue; } - continue; activate_locked_split: / * The tail pages that are failed to add into swap cache - * reach here. Fixup nr_scanned and nr_pages. + * reach here. Fixup nr_scanned. / - if (nr_pages > 1) { + if (nr_pages > 1) sc->nr_scanned -= (nr_pages - 1); - nr_pages = 1; - } activate_locked: - / Not a candidate for swapping, so reclaim swap space. / - if (folio_test_swapcache(folio) && - (mem_cgroup_swap_full(folio) \|\| folio_test_mlocked(folio))) - folio_free_swap(folio); - VM_BUG_ON_FOLIO(folio_test_active(folio), folio); - if (!folio_test_mlocked(folio)) { - int type = folio_is_file_lru(folio); - folio_set_active(folio); - stat->nr_activate[type] += nr_pages; - count_memcg_folio_events(folio, PGACTIVATE, nr_pages); - } + folio_activate_locked(folio, stat); keep_locked: folio_unlock(folio); keep: - list_add(&folio->lru, &ret_folios); + list_add(&folio->lru, &state.ret_folios); VM_BUG_ON_FOLIO(folio_test_lru(folio) \|\| folio_test_unevictable(folio), folio); } + if (folio_batch_count(&pageout_folios)) { + folio_batch_pageout(&pageout_folios, &state, sc, stat, + &ctx, folio_list); + } / 'folio_list' is always empty here / / Migrate folios selected for demotion / nr_demoted = demote_folio_list(&demote_folios, pgdat, memcg); - nr_reclaimed += nr_demoted; + state.nr_reclaimed += nr_demoted; stat->nr_demoted += nr_demoted; / Folios that could not be demoted are still in @demote_folios / if (!list_empty(&demote_folios)) { @@ -1683,15 +1843,15 @@ static unsigned int shrink_folio_list(struct list_head folio_list, pgactivate = stat->nr_activate[0] + stat->nr_activate[1]; - mem_cgroup_uncharge_folios(&free_folios); + mem_cgroup_uncharge_folios(&state.free_folios); try_to_unmap_flush(); - free_unref_folios(&free_folios); + free_unref_folios(&state.free_folios); - list_splice(&ret_folios, folio_list); + list_splice(&state.ret_folios, folio_list); count_vm_events(PGACTIVATE, pgactivate); swap_write_submit(&ctx); - return nr_reclaimed; + return state.nr_reclaimed; } unsigned int reclaim_clean_pages_from_list(struct zone *zone,
35/3	2026/11/01 07:38	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 8909 output: 23 thoughts: 1349 Thoughts: KMSAN Needs Assessment: mm/vmscan.c Refactor Okay, let's break this down. The task is to decide if this `mm/vmscan.c` patch warrants a dedicated KMSAN fuzzing session. The rule is clear: only if the code changes introduce uninitialized memory risks that KMSAN specifically catches, and that KASAN, LOCKDEP, or other standard detectors won't. Dedicated KMSAN is expensive, so we only use it when necessary. The patch refactors `shrink_folio_list()`, which handles page reclaim. It's moving towards batching pageouts of folios. A number of helpers and a new `struct reclaim_folio_state` are introduced. First, I need to check for the tell-tale signs: 1. Data copies to userspace? No. This is all in kernel-land, specifically memory management. No immediate risk there. 2. Uninitialized variables or struct fields? I need to be thorough about this. Let's see... * `struct reclaim_folio_state state = {};` is zero-initialized. Good. * `INIT_LIST_HEAD(&state.ret_folios);` initializes the list head. Fine. * `folio_batch_init(&state.free_folios);` initializes the batch. Okay. * `folio_batch_init(&pageout_folios);` initializes the batch. Okay, seems safe. * `struct swap_io_ctx ctx = {};` is zero-initialized. Good. * `memset(stat, 0, sizeof(stat));` clears `stat`. Another check. So, at face value, all the new or modified structures seem to be initialized properly, either with explicit zeroing or initialization functions. The key change is in `shrink_folio_list()` itself. Instead of immediate `pageout` calls, it now batches folios. It populates a `pageout_folios` batch, then calls `folio_batch_pageout`. Inside `folio_batch_pageout`, the folios are re-locked, revalidated, flushed, and the relevant reclaim functions are called. The `folio_batch_pageout` function is interesting: unsigned int nr = folio_batch_count(batch); unsigned int i; The comment says `folio_batch_reinit` leaves the array intact. This bears further investigation. I need to understand how the `folio_batch` structure and its associated `folio_batch_reinit` function actually work. I will now check the definition of `folio_batch` and `folio_batch_reinit` in the kernel source to confirm that there are no uninitialized variables or memory exposures. Conclusion:* At this point, pending a check of the batch initialization and reinit functions, I don't see any obvious uninitialized memory risks that are KMSAN-specific. KASAN and friends should catch any out-of-bounds accesses or similar issues. Assuming the batch reinit code checks out, I'm leaning towards `NeedsKMSAN=false` for this patch, as it is just page reclaim / vmscan in mm.
36/3	2026/11/01 07:38	tool	grepper	0m Args: { "Expression": "static inline void folio_batch_reinit" } Results: { "Output": "include/linux/folio_batch.h=41=static inline void folio_batch_init(struct folio_batch fbatch)\n--\ninclude/linux/folio_batch.h-47-\ninclude/linux/folio_batch.h:48:static inline void folio_batch_reinit(struct folio_batch fbatch)\ninclude/linux/folio_batch.h-49-{\n" }
37/3	2026/11/01 07:39	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11094 output: 36 thoughts: 21 Thoughts: Here's a summary of my thought process, expert to expert: Diving into Folio Batching Okay, let's zero in. I need to understand the folio batching implementation, particularly how they're managed internally. Specifically, I'm going to jump into `include/linux/folio_batch.h`. I'm guessing that line 48 should give me a good entry point. I expect to find some fundamental data structures or key function declarations there that will lay out the core mechanism of how folios are grouped and processed in batches. This is likely where the batch descriptor structures or initialization routines will reside. I'm hoping to quickly grasp the memory layout and any associated locking primitives used to protect the batch operations. Let's see what we can find.
38/3	2026/11/01 07:39	tool	read-file	0m Args: { "File": "include/linux/folio_batch.h", "FirstLine": 30, "LineCount": 40 } Results: { "Contents": " 30:\t\tunsigned char i;\n 31:\t\tbool percpu_pvec_drained;\n 32:\t\tstruct folio folios[FOLIO_BATCH_SIZE];\n 33:\t};\n 34:\t\n 35:\t/\n 36:\t folio_batch_init() - Initialise a batch of folios\n 37:\t * @fbatch: The folio batch.\n 38:\t \n 39:\t A freshly initialised folio_batch contains zero folios.\n 40:\t /\n 41:\tstatic inline void folio_batch_init(struct folio_batch fbatch)\n 42:\t{\n 43:\t\tfbatch-\u003enr = 0;\n 44:\t\tfbatch-\u003ei = 0;\n 45:\t\tfbatch-\u003epercpu_pvec_drained = false;\n 46:\t}\n 47:\t\n 48:\tstatic inline void folio_batch_reinit(struct folio_batch fbatch)\n 49:\t{\n 50:\t\tfbatch-\u003enr = 0;\n 51:\t\tfbatch-\u003ei = 0;\n 52:\t}\n 53:\t\n 54:\tstatic inline unsigned int folio_batch_count(const struct folio_batch fbatch)\n 55:\t{\n 56:\t\treturn fbatch-\u003enr;\n 57:\t}\n 58:\t\n 59:\tstatic inline unsigned int folio_batch_space(const struct folio_batch fbatch)\n 60:\t{\n 61:\t\treturn FOLIO_BATCH_SIZE - fbatch-\u003enr;\n 62:\t}\n 63:\t\n 64:\t/\n 65:\t folio_batch_add() - Add a folio to a batch.\n 66:\t * @fbatch: The folio batch.\n 67:\t * @folio: The folio to add.\n 68:\t \n 69:\t The folio is added to the end of the batch.\n" }
39/3	2026/11/01 07:39	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11829 output: 257 thoughts: 1219 Thoughts: My Assessment of the Patch's KMSAN Applicability Okay, let's break this down. The patch introduces changes to folio reclamation and pageout operations, specifically introducing `folio_batch_pageout`, `folio_try_pageout`, and `folio_try_reclaim_free`. My initial thought is to assess potential risks, specifically focusing on the areas KMSAN is designed to catch: uninitialized memory usage. First, I see that `folio_batch_reinit` zeros out the `nr` and `i` fields, and the iteration logic in `folio_batch_pageout` carefully handles the batch's contents. I'm checking for out-of-bounds access, locking issues (deadlocks), use-after-free conditions, page refcounting errors, and, critically, uninitialized memory reads. KASAN and LOCKDEP should catch the first few. I am particularly concerned with that last item: uninitialized memory. Looking closer at the code, I see that the `struct reclaim_folio_state` and related structures (`state.ret_folios`, `state.free_folios`, `pageout_folios`) are explicitly initialized, either to zero or using `INIT_LIST_HEAD` and `folio_batch_init`. I'm confident that all local variables used in `shrink_folio_list`, `folio_batch_pageout`, the `try_` functions, and `folio_activate_locked` are initialized before use. There are no exposed kernel structures going to user space and no padding or uninitialized structs being exposed. No info leaks, either. Therefore, this patch does not* introduce any uninitialized memory risks. Any bugs that might arise here are more likely related to concurrency (locking, race conditions), refcounting, or memory management logic, which are precisely the areas KASAN, LOCKDEP, and page allocator debug configs handle well. KMSAN isn't the right tool here. Now, let's rigorously check the KMSAN criteria. Does this patch: 1. Modify kernel structures sent to userspace? No. 2. Introduce conditional logic based on uninitialized variables? No. 3. Involve allocation or initialization of complex data structures where uninitialized fields could be read later? No. 4. Affect bounds checks in a way that allows access to uninitialized bytes? No. This clearly fails to satisfy any of the conditions that warrant KMSAN. The risks here are more related to concurrency (locking/deadlocks), reference counting, or memory management. Those bugs are already well-covered by KASAN and LOCKDEP. KMSAN is specifically for finding uninitialized memory reads and information leaks, which is not relevant in this scenario. In conclusion, I'm setting `NeedsKMSAN=false`. The standard KASAN/LOCKDEP builds will provide the necessary level of assurance for this patch. I can now generate a KMSAN reasoning string that summarizes the changes, assesses the uninitialized memory aspect, contrasts KASAN and KMSAN, and concludes that a dedicated KMSAN session isn't warranted. Let's call `set-results`.
40/3	2026/11/01 07:39	tool	set-results	0m Args: { "KMSANReasoning": "The patch refactors pageout and reclamation logic in mm/vmscan.c by batching dirty folio writebacks and modularizing helpers (folio_batch_pageout, folio_try_reclaim_free, folio_try_pageout, folio_activate_locked, folio_try_unmap).\n\nAll newly introduced stack structures and batches (such as struct reclaim_folio_state and pageout_folios) are explicitly zero-initialized and initialized with folio_batch_init() and INIT_LIST_HEAD(). The code does not expose any uninitialized variables, conditional branches on uninitialized state, or data copies to user space (info-leaks).\n\nThe potential risks introduced by this change are memory management logic errors, reference counting inconsistencies, race conditions from unlocking and re-locking folios, or use-after-free conditions. These classes of bugs are thoroughly covered by KASAN, LOCKDEP, and internal VM asserts (VM_WARN_ON/VM_BUG_ON). Because there are no uninitialized memory risks that KMSAN specifically detects, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch refactors pageout and reclamation logic in mm/vmscan.c by batching dirty folio writebacks and modularizing helpers (folio_batch_pageout, folio_try_reclaim_free, folio_try_pageout, folio_activate_locked, folio_try_unmap).\n\nAll newly introduced stack structures and batches (such as struct reclaim_folio_state and pageout_folios) are explicitly zero-initialized and initialized with folio_batch_init() and INIT_LIST_HEAD(). The code does not expose any uninitialized variables, conditional branches on uninitialized state, or data copies to user space (info-leaks).\n\nThe potential risks introduced by this change are memory management logic errors, reference counting inconsistencies, race conditions from unlocking and re-locking folios, or use-after-free conditions. These classes of bugs are thoroughly covered by KASAN, LOCKDEP, and internal VM asserts (VM_WARN_ON/VM_BUG_ON). Because there are no uninitialized memory risks that KMSAN specifically detects, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false }

LLM Calls Summary:
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Tool Calls Summary:
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