| Seq | Timestamp | Type | Name | Duration |
|---|---|---|---|---|
| 0/0 | 2026/09/22 16:33 | flow | patch-triage |
2mArgs:null Results: {
"EnableConfigs": null,
"FocusSymbols": [
"shrink_folio_list",
"folio_try_reclaim_free",
"folio_try_pageout",
"folio_try_unmap",
"folio_activate_locked"
],
"KMSANReasoning": "The patch is a refactoring of the folio reclamation loop in `shrink_folio_list()` (`mm/vmscan.c`). It extracts monolithic blocks of code into smaller helper functions: `folio_activate_locked()`, `folio_try_reclaim_free()`, `folio_try_pageout()`, and `folio_try_unmap()`.\n\nNo new data structures, stack/heap allocations, or copies to user space (such as copy_to_user or netlink/ioctl transfers) are introduced. All local variables and pointers are properly initialized, and no uninitialized memory paths or info-leaks are created or exposed. Any potential regressions or bugs from this refactoring (e.g., refcounting issues, lock handling, or use-after-free) would be detected by standard debugging facilities (KASAN, page-refcount checks, and lockdep), making a dedicated KMSAN fuzzing session unnecessary.",
"NeedsKMSAN": false,
"Reasoning": "The patch refactors the core page reclamation routine shrink_folio_list() in mm/vmscan.c into several helper functions (folio_activate_locked, folio_try_reclaim_free, folio_try_pageout, and folio_try_unmap). It alters state accounting and handling during folio splitting and pageout, and introduces new runtime assertions (such as VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio)). This is reachable core memory management code executed under memory pressure and warrants fuzzing.",
"WorthFuzzing": true
} |
| 1/1 | 2026/09/22 16:33 | action | read-patch-diff |
0mArgs:null Results: {
"PatchDiff": "commit 7be148f91d6dd00d1d9ac102004804b1e9a3e38e\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Tue Sep 22 16:33:06 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/mm/vmscan.c b/mm/vmscan.c\nindex e200ce3eb056b..71b507011603d 100644\n--- a/mm/vmscan.c\n+++ b/mm/vmscan.c\n@@ -1155,8 +1155,203 @@ 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+enum folio_reclaim_result {\n+\tFOLIO_RECLAIM_KEEP,\n+\tFOLIO_RECLAIM_ACTIVATE,\n+\tFOLIO_RECLAIM_SUCCESS,\n+};\n+\n+static enum folio_reclaim_result folio_try_reclaim_free(struct folio *folio,\n+\t\tstruct folio_batch *free_folios,\n+\t\tstruct scan_control *sc,\n+\t\tunsigned int *nr_reclaimed)\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\t*nr_reclaimed += nr_pages;\n+\t\t\treturn FOLIO_RECLAIM_SUCCESS;\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+\t*nr_reclaimed += nr_pages;\n+\n+\tfolio_unqueue_deferred_split(folio);\n+\tif (folio_batch_add(free_folios, folio) == 0) {\n+\t\tmem_cgroup_uncharge_folios(free_folios);\n+\t\ttry_to_unmap_flush();\n+\t\tfree_unref_folios(free_folios);\n+\t}\n+\treturn FOLIO_RECLAIM_SUCCESS;\n+}\n+\n+enum folio_pageout_result {\n+\tFOLIO_PAGEOUT_KEEP_LOCKED,\n+\tFOLIO_PAGEOUT_KEEP_UNLOCKED,\n+\tFOLIO_PAGEOUT_ACTIVATE,\n+\tFOLIO_PAGEOUT_FREE,\t/* folio is locked, hand it to folio_try_reclaim_free() */\n+};\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 *mapping = folio_mapping(folio);\n+\tunsigned 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_FREE;\n+\t}\n+\tunreachable();\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- * shrink_folio_list() returns the number of reclaimed pages\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@@ -1433,36 +1628,9 @@ 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 +1642,6 @@ 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@@ -1495,152 +1662,43 @@ 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 */\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\tswitch (folio_try_pageout(folio, sc, \u0026ctx, folio_list)) {\n+\t\t\tcase FOLIO_PAGEOUT_ACTIVATE:\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\tcase FOLIO_PAGEOUT_KEEP_LOCKED:\n+\t\t\t\tgoto keep_locked;\n+\t\t\tcase FOLIO_PAGEOUT_KEEP_UNLOCKED:\n+\t\t\t\tgoto keep;\n+\t\t\tcase FOLIO_PAGEOUT_FREE:\n+\t\t\t\tbreak;\t/* folio is locked; try to free it below */\n \t\t\t}\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, \u0026free_folios, sc,\n+\t\t\t\t\t \u0026nr_reclaimed)) {\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_SUCCESS:\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"
} |
| 2/1 | 2026/09/22 16:33 | agent | patch-evaluator |
1mModel:core Args: null Results: {
"EnableConfigs": null,
"FocusSymbols": [
"shrink_folio_list",
"folio_try_reclaim_free",
"folio_try_pageout",
"folio_try_unmap",
"folio_activate_locked"
],
"Reasoning": "The patch refactors the core page reclamation routine shrink_folio_list() in mm/vmscan.c into several helper functions (folio_activate_locked, folio_try_reclaim_free, folio_try_pageout, and folio_try_unmap). It alters state accounting and handling during folio splitting and pageout, and introduces new runtime assertions (such as VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio)). This is reachable core memory management code executed under memory pressure and warrants 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 7be148f91d6dd00d1d9ac102004804b1e9a3e38e
Author: syz-cluster <triage@syzkaller.com>
Date: Tue Sep 22 16:33:06 2026 +0000
syz-cluster: applied patch under review
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e200ce3eb056b..71b507011603d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1155,8 +1155,203 @@ 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);
+ }
+}
+
+enum folio_reclaim_result {
+ FOLIO_RECLAIM_KEEP,
+ FOLIO_RECLAIM_ACTIVATE,
+ FOLIO_RECLAIM_SUCCESS,
+};
+
+static enum folio_reclaim_result folio_try_reclaim_free(struct folio *folio,
+ struct folio_batch *free_folios,
+ struct scan_control *sc,
+ unsigned int *nr_reclaimed)
+{
+ 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.
+ */
+ *nr_reclaimed += nr_pages;
+ return FOLIO_RECLAIM_SUCCESS;
+ }
+ }
+
+ 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);
+ *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);
+ }
+ return FOLIO_RECLAIM_SUCCESS;
+}
+
+enum folio_pageout_result {
+ FOLIO_PAGEOUT_KEEP_LOCKED,
+ FOLIO_PAGEOUT_KEEP_UNLOCKED,
+ FOLIO_PAGEOUT_ACTIVATE,
+ FOLIO_PAGEOUT_FREE, /* folio is locked, hand it to folio_try_reclaim_free() */
+};
+
+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 *mapping = folio_mapping(folio);
+ 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_FREE;
+ }
+ unreachable();
+}
+
+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;
+}
+
/*
- * shrink_folio_list() returns the number of reclaimed pages
+ * 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,
@@ -1433,36 +1628,9 @@ 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 +1642,6 @@ 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)) {
/*
@@ -1495,152 +1662,43 @@ 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.
*/
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;
- }
+ switch (folio_try_pageout(folio, sc, &ctx, folio_list)) {
+ case FOLIO_PAGEOUT_ACTIVATE:
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;
- }
+ case FOLIO_PAGEOUT_KEEP_LOCKED:
+ goto keep_locked;
+ case FOLIO_PAGEOUT_KEEP_UNLOCKED:
+ goto keep;
+ case FOLIO_PAGEOUT_FREE:
+ break; /* folio is locked; try to free it below */
}
}
- 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, &free_folios, sc,
+ &nr_reclaimed)) {
+ 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_SUCCESS:
+ 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:
|
| 3/2 | 2026/09/22 16:33 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 7724 output: 31 thoughts: 114 Thoughts: **Evaluating the Submitted Patch Series** Okay, so the user wants me to take a look at a patch series, specifically one applied as the HEAD commit in their workspace. My first instinct is to get a solid grasp of what's been changed and the context within the repository. Let's start with a thorough inspection. Since the patch modifies `mm/vmscan.c`, that's the focal point. I'll lean on the available tools - `git log`, `git diff`, or if those aren't directly accessible, I can always fall back on the `read-file` and `grepper` tools to achieve the same result, and take a look at the code. I need to understand the intent and impact of these changes. Specifically, I'll be targeting lines around 1155 and then lines 1433 through 1662 in `mm/vmscan.c`. That should give me a good handle on the primary modifications made by the patch. I'll be looking for potential side effects, performance implications, and whether the changes align with established coding practices and kernel design principles. A quick look at the surrounding code might also be needed. |
| 4/2 | 2026/09/22 16:33 | tool | grepper |
0mArgs:{
"Expression": "folio_activate_locked",
"PathPrefix": "mm/vmscan.c"
}Results: {
"Output": "mm/vmscan.c=1143=static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)\n--\nmm/vmscan.c-1158-/* Activate an isolated, locked folio and account the activation. */\nmm/vmscan.c:1159:static void folio_activate_locked(struct folio *folio,\nmm/vmscan.c-1160-\t\tstruct reclaim_stat *stat)\n--\nmm/vmscan.c=1276=static enum folio_pageout_result folio_try_pageout(struct folio *folio,\n--\nmm/vmscan.c-1288-\t\t * function and be accounted then. There is no need to\nmm/vmscan.c:1289:\t\t * clamp nr_pages here: folio_activate_locked() derives\nmm/vmscan.c-1290-\t\t * the count from folio_nr_pages() itself.\n--\nmm/vmscan.c=1356=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1700-activate_locked:\nmm/vmscan.c:1701:\t\tfolio_activate_locked(folio, stat);\nmm/vmscan.c-1702-keep_locked:\n"
} |
| 5/2 | 2026/09/22 16:33 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8452 output: 36 thoughts: 123 Thoughts: **Analyzing the vmscan.c Patch** Okay, let's dive into this patch. I see they're really going after `shrink_folio_list()` in `mm/vmscan.c`. Looks like they're breaking it down into more manageable, and potentially more efficient, pieces. Good. I'm seeing a clear pattern here – we're moving towards modularization and probably some improved locking strategy too. So, they've introduced a few new helpers: `folio_activate_locked()`, `folio_try_reclaim_free()`, `folio_try_pageout()`, and `folio_try_unmap()`. Interesting names, all hinting at specific functionalities, and I assume at a more granular locking scheme. I'll need to see how they're being used within `shrink_folio_list()`. It's likely these functions will allow for better concurrency, reducing contention on the folio lists and allowing for faster reclaim. Time to dig into the code itself. Let me check out lines 1150-1360 in `mm/vmscan.c`. That should give me the meat of the refactoring and reveal the real details behind this approach. I expect to see how these helpers are chained together and how they interact with the overall reclaim process. I'll be looking for changes in locking, error handling, and, of course, any potential performance implications. This is the part that will tell the real story. |
| 6/2 | 2026/09/22 16:33 | tool | read-file |
0mArgs:{
"File": "mm/vmscan.c",
"FirstLine": 1155,
"LineCount": 100
}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:\tenum folio_reclaim_result {\n1181:\t\tFOLIO_RECLAIM_KEEP,\n1182:\t\tFOLIO_RECLAIM_ACTIVATE,\n1183:\t\tFOLIO_RECLAIM_SUCCESS,\n1184:\t};\n1185:\t\n1186:\tstatic enum folio_reclaim_result folio_try_reclaim_free(struct folio *folio,\n1187:\t\t\tstruct folio_batch *free_folios,\n1188:\t\t\tstruct scan_control *sc,\n1189:\t\t\tunsigned int *nr_reclaimed)\n1190:\t{\n1191:\t\tconst unsigned int nr_pages = folio_nr_pages(folio);\n1192:\t\tstruct address_space *mapping = folio_mapping(folio);\n1193:\t\n1194:\t\t/*\n1195:\t\t * If the folio has buffers, try to free the buffer mappings\n1196:\t\t * associated with this folio. If we succeed we try to free\n1197:\t\t * the folio as well.\n1198:\t\t *\n1199:\t\t * We do this even if the folio is dirty.\n1200:\t\t * filemap_release_folio() does not perform I/O, but it is\n1201:\t\t * possible for a folio to have the dirty flag set, but it\n1202:\t\t * is actually clean (all its buffers are clean). This\n1203:\t\t * happens if the buffers were written out directly, with\n1204:\t\t * bh_submit(). ext3 will do this, as well as the blockdev\n1205:\t\t * mapping. filemap_release_folio() will discover that\n1206:\t\t * cleanness and will drop the buffers and mark the folio\n1207:\t\t * clean - it can be freed.\n1208:\t\t *\n1209:\t\t * Rarely, folios can have buffers and no -\u003emapping. These\n1210:\t\t * are the folios which were not successfully invalidated in\n1211:\t\t * truncate_cleanup_folio(). We try to drop those buffers\n1212:\t\t * here and if that worked, and the folio is no longer\n1213:\t\t * mapped into process address space (refcount == 1) it can\n1214:\t\t * be freed. Otherwise, leave the folio on the LRU so it is\n1215:\t\t * swappable.\n1216:\t\t */\n1217:\t\tif (folio_needs_release(folio)) {\n1218:\t\t\tif (!filemap_release_folio(folio, sc-\u003egfp_mask))\n1219:\t\t\t\treturn FOLIO_RECLAIM_ACTIVATE;\n1220:\t\n1221:\t\t\tif (!mapping \u0026\u0026 folio_ref_count(folio) == 1) {\n1222:\t\t\t\tfolio_unlock(folio);\n1223:\t\t\t\tif (folio_put_testzero(folio))\n1224:\t\t\t\t\tgoto free_it;\n1225:\t\n1226:\t\t\t\t/*\n1227:\t\t\t\t * Rare race with speculative reference. The\n1228:\t\t\t\t * speculative reference will free this folio\n1229:\t\t\t\t * shortly, so we may increment nr_reclaimed here\n1230:\t\t\t\t * and leave it off the LRU.\n1231:\t\t\t\t */\n1232:\t\t\t\t*nr_reclaimed += nr_pages;\n1233:\t\t\t\treturn FOLIO_RECLAIM_SUCCESS;\n1234:\t\t\t}\n1235:\t\t}\n1236:\t\n1237:\t\tif (folio_test_lazyfree(folio)) {\n1238:\t\t\t/* follow __remove_mapping for reference */\n1239:\t\t\tif (!folio_ref_freeze(folio, 1))\n1240:\t\t\t\treturn FOLIO_RECLAIM_KEEP;\n1241:\t\t\t/*\n1242:\t\t\t * The folio has only one reference left, which is\n1243:\t\t\t * from the isolation. After the caller puts the\n1244:\t\t\t * folio back on the lru and drops the reference, the\n1245:\t\t\t * folio will be freed anyway. It doesn't matter\n1246:\t\t\t * which lru it goes on. So we don't bother checking\n1247:\t\t\t * the dirty flag here.\n1248:\t\t\t */\n1249:\t\t\tcount_vm_events(PGLAZYFREED, nr_pages);\n1250:\t\t\tcount_memcg_folio_events(folio, PGLAZYFREED, nr_pages);\n1251:\t\t} else if (!mapping || !__remove_mapping(mapping, folio, true,\n1252:\t\t\t\t\t\t\t\tsc-\u003etarget_mem_cgroup))\n1253:\t\t\treturn FOLIO_RECLAIM_KEEP;\n1254:\t\n"
} |
| 7/2 | 2026/09/22 16:33 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 10531 output: 36 thoughts: 20 Thoughts: Okay, here's my attempt at summarizing the thought process, as requested, in the first person and assuming an expert audience, focusing on the specified lines: **Diving Deeper: Lines 1255-1355** Alright, let's get into the weeds, specifically lines 1255 to 1355. My initial scan already indicates this section's likely to deal with [insert your expert knowledge here, based on context that would be in the original text you are summarizing. Provide a general area like "model validation" or "experimental methodology" to provide the appropriate response]. Knowing the broader structure, I anticipate [mention what you expect to find, from your expert viewpoint]. I'll be looking closely for [mention specific technical terms or concepts relevant to your field]. The nuance I’m particularly keen on catching is [specific nuance]. Any deviation from established methodologies or unexpected findings will immediately grab my attention. I want to assess, quickly, if the author's argument is sufficiently substantiated, if the methods applied are appropriate and, if the work in question offers any advance in the state of the art. I'll need to rapidly evaluate whether [mention specific concerns that might arise in your area], and if the arguments are logically consistent and defensible against standard counterarguments. I'm going to pay special attention to the use of [technical term] in this context, because [expert reason]. In general, this requires a swift, yet careful, dissection of the work to gauge its validity. |
| 8/2 | 2026/09/22 16:34 | tool | read-file |
0mArgs:{
"File": "mm/vmscan.c",
"FirstLine": 1255,
"LineCount": 100
}Results: {
"Contents": "1255:\t\tfolio_unlock(folio);\n1256:\tfree_it:\n1257:\t\tVM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);\n1258:\t\t*nr_reclaimed += nr_pages;\n1259:\t\n1260:\t\tfolio_unqueue_deferred_split(folio);\n1261:\t\tif (folio_batch_add(free_folios, folio) == 0) {\n1262:\t\t\tmem_cgroup_uncharge_folios(free_folios);\n1263:\t\t\ttry_to_unmap_flush();\n1264:\t\t\tfree_unref_folios(free_folios);\n1265:\t\t}\n1266:\t\treturn FOLIO_RECLAIM_SUCCESS;\n1267:\t}\n1268:\t\n1269:\tenum folio_pageout_result {\n1270:\t\tFOLIO_PAGEOUT_KEEP_LOCKED,\n1271:\t\tFOLIO_PAGEOUT_KEEP_UNLOCKED,\n1272:\t\tFOLIO_PAGEOUT_ACTIVATE,\n1273:\t\tFOLIO_PAGEOUT_FREE,\t/* folio is locked, hand it to folio_try_reclaim_free() */\n1274:\t};\n1275:\t\n1276:\tstatic enum folio_pageout_result folio_try_pageout(struct folio *folio,\n1277:\t\t\tstruct scan_control *sc, struct swap_io_ctx *ctx,\n1278:\t\t\tstruct list_head *folio_list)\n1279:\t{\n1280:\t\tstruct address_space *mapping = folio_mapping(folio);\n1281:\t\tunsigned int nr_pages = folio_nr_pages(folio);\n1282:\t\n1283:\t\tswitch (pageout(ctx, mapping, folio, folio_list)) {\n1284:\t\tcase PAGE_ACTIVATE:\n1285:\t\t\t/*\n1286:\t\t\t * If shmem folio is split when writeback to swap, the\n1287:\t\t\t * tail pages will make their own pass through this\n1288:\t\t\t * function and be accounted then. There is no need to\n1289:\t\t\t * clamp nr_pages here: folio_activate_locked() derives\n1290:\t\t\t * the count from folio_nr_pages() itself.\n1291:\t\t\t */\n1292:\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n1293:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1294:\t\t\treturn FOLIO_PAGEOUT_ACTIVATE;\n1295:\t\tcase PAGE_KEEP:\n1296:\t\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n1297:\t\tcase PAGE_SUCCESS:\n1298:\t\t\tif (nr_pages \u003e 1 \u0026\u0026 !folio_test_large(folio))\n1299:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1300:\t\n1301:\t\t\tif (folio_test_writeback(folio))\n1302:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1303:\t\t\tif (folio_test_dirty(folio))\n1304:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1305:\t\n1306:\t\t\t/*\n1307:\t\t\t * A synchronous write - probably a ramdisk. Go ahead\n1308:\t\t\t * and try to reclaim the folio.\n1309:\t\t\t */\n1310:\t\t\tif (!folio_trylock(folio))\n1311:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_UNLOCKED;\n1312:\t\t\tif (folio_test_dirty(folio) || folio_test_writeback(folio))\n1313:\t\t\t\treturn FOLIO_PAGEOUT_KEEP_LOCKED;\n1314:\t\t\tfallthrough;\n1315:\t\tcase PAGE_CLEAN:\n1316:\t\t\treturn FOLIO_PAGEOUT_FREE;\n1317:\t\t}\n1318:\t\tunreachable();\n1319:\t}\n1320:\t\n1321:\tstatic bool folio_try_unmap(struct folio *folio, struct reclaim_stat *stat,\n1322:\t\t\tunsigned int nr_pages)\n1323:\t{\n1324:\t\tenum ttu_flags flags = TTU_BATCH_FLUSH;\n1325:\t\tconst bool was_swapbacked = folio_test_swapbacked(folio);\n1326:\t\n1327:\t\tif (folio_test_pmd_mappable(folio))\n1328:\t\t\tflags |= TTU_SPLIT_HUGE_PMD;\n1329:\t\t/*\n1330:\t\t * Without TTU_SYNC, try_to_unmap will only begin to hold PTL\n1331:\t\t * from the first present PTE within a large folio. Some\n1332:\t\t * initial PTEs might be skipped due to races with parallel\n1333:\t\t * PTE writes in which PTEs can be cleared temporarily before\n1334:\t\t * being written new present values. This will lead to a large\n1335:\t\t * folio is still mapped while some subpages have been\n1336:\t\t * partially unmapped after try_to_unmap; TTU_SYNC helps\n1337:\t\t * try_to_unmap acquire PTL from the first PTE, eliminating the\n1338:\t\t * influence of temporary PTE values.\n1339:\t\t */\n1340:\t\tif (folio_test_large(folio))\n1341:\t\t\tflags |= TTU_SYNC;\n1342:\t\n1343:\t\ttry_to_unmap(folio, flags);\n1344:\t\tif (folio_mapped(folio)) {\n1345:\t\t\tstat-\u003enr_unmap_fail += nr_pages;\n1346:\t\t\tif (!was_swapbacked \u0026\u0026 folio_test_swapbacked(folio))\n1347:\t\t\t\tstat-\u003enr_lazyfree_fail += nr_pages;\n1348:\t\t\treturn false;\n1349:\t\t}\n1350:\t\treturn true;\n1351:\t}\n1352:\t\n1353:\t/*\n1354:\t * Reclaimed folios are counted in the return value.\n"
} |
| 9/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 12517 output: 36 thoughts: 26 Thoughts: Okay, here's my take on those lines in `mm/vmscan.c`. **Diving into vmscan.c: A Specific Section for Deeper Understanding** Right, let's zero in on lines 1620 to 1715 within `mm/vmscan.c`. I know this area holds some critical logic related to the virtual memory scanner, so I'm keen to see what's being done. My immediate thought is, what specific aspects of memory reclaim are being addressed in this segment? Is this related to a particular page type, a specific reclaim strategy, or a certain optimization? I need to understand the *why* behind this section to truly grasp its significance. Are we dealing with active or inactive pages, file-backed or anonymous memory, and how are the reclaim decisions being influenced? It is also likely that I might be able to glean what the context of that function is and what the function is trying to achieve. Is there any obvious loop or conditional logic that will allow me to track the execution flow? |
| 10/2 | 2026/09/22 16:34 | tool | read-file |
0mArgs:{
"File": "mm/vmscan.c",
"FirstLine": 1620,
"LineCount": 100
}Results: {
"Contents": "1620:\t\t\t * then.\n1621:\t\t\t */\n1622:\t\t\tif ((nr_pages \u003e 1) \u0026\u0026 !folio_test_large(folio)) {\n1623:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1624:\t\t\t\tnr_pages = 1;\n1625:\t\t\t}\n1626:\t\n1627:\t\t\t/*\n1628:\t\t\t * The folio is mapped into the page tables of one or more\n1629:\t\t\t * processes. Try to unmap it here.\n1630:\t\t\t */\n1631:\t\t\tif (folio_mapped(folio) \u0026\u0026\n1632:\t\t\t !folio_try_unmap(folio, stat, nr_pages))\n1633:\t\t\t\tgoto activate_locked;\n1634:\t\n1635:\t\t\t/*\n1636:\t\t\t * Folio is unmapped now so it cannot be newly pinned anymore.\n1637:\t\t\t * No point in trying to reclaim folio if it is pinned.\n1638:\t\t\t * Furthermore we don't want to reclaim underlying fs metadata\n1639:\t\t\t * if the folio is pinned and thus potentially modified by the\n1640:\t\t\t * pinning process as that may upset the filesystem.\n1641:\t\t\t */\n1642:\t\t\tif (folio_maybe_dma_pinned(folio))\n1643:\t\t\t\tgoto activate_locked;\n1644:\t\n1645:\t\t\tif (folio_test_dirty(folio)) {\n1646:\t\t\t\tif (folio_is_file_lru(folio)) {\n1647:\t\t\t\t\t/*\n1648:\t\t\t\t\t * Immediately reclaim when written back.\n1649:\t\t\t\t\t * Similar in principle to folio_deactivate()\n1650:\t\t\t\t\t * except we already have the folio isolated\n1651:\t\t\t\t\t * and know it's dirty\n1652:\t\t\t\t\t */\n1653:\t\t\t\t\tnode_stat_mod_folio(folio, NR_VMSCAN_IMMEDIATE,\n1654:\t\t\t\t\t\t\tnr_pages);\n1655:\t\t\t\t\tif (!folio_test_reclaim(folio))\n1656:\t\t\t\t\t\tfolio_set_reclaim(folio);\n1657:\t\n1658:\t\t\t\t\tgoto activate_locked;\n1659:\t\t\t\t}\n1660:\t\n1661:\t\t\t\tif (!may_enter_fs(folio, sc-\u003egfp_mask))\n1662:\t\t\t\t\tgoto keep_locked;\n1663:\t\t\t\tif (!sc-\u003emay_writepage)\n1664:\t\t\t\t\tgoto keep_locked;\n1665:\t\t\t\t/*\n1666:\t\t\t\t * Folio is dirty. Flush the TLB if a writable entry\n1667:\t\t\t\t * potentially exists to avoid CPU writes after I/O\n1668:\t\t\t\t * starts and then write it out here.\n1669:\t\t\t\t */\n1670:\t\t\t\ttry_to_unmap_flush_dirty();\n1671:\t\t\t\tswitch (folio_try_pageout(folio, sc, \u0026ctx, folio_list)) {\n1672:\t\t\t\tcase FOLIO_PAGEOUT_ACTIVATE:\n1673:\t\t\t\t\tgoto activate_locked;\n1674:\t\t\t\tcase FOLIO_PAGEOUT_KEEP_LOCKED:\n1675:\t\t\t\t\tgoto keep_locked;\n1676:\t\t\t\tcase FOLIO_PAGEOUT_KEEP_UNLOCKED:\n1677:\t\t\t\t\tgoto keep;\n1678:\t\t\t\tcase FOLIO_PAGEOUT_FREE:\n1679:\t\t\t\t\tbreak;\t/* folio is locked; try to free it below */\n1680:\t\t\t\t}\n1681:\t\t\t}\n1682:\t\n1683:\t\t\tswitch (folio_try_reclaim_free(folio, \u0026free_folios, sc,\n1684:\t\t\t\t\t\t \u0026nr_reclaimed)) {\n1685:\t\t\tcase FOLIO_RECLAIM_ACTIVATE:\n1686:\t\t\t\tgoto activate_locked;\n1687:\t\t\tcase FOLIO_RECLAIM_KEEP:\n1688:\t\t\t\tgoto keep_locked;\n1689:\t\t\tcase FOLIO_RECLAIM_SUCCESS:\n1690:\t\t\t\tcontinue;\n1691:\t\t\t}\n1692:\t\n1693:\tactivate_locked_split:\n1694:\t\t\t/*\n1695:\t\t\t * The tail pages that are failed to add into swap cache\n1696:\t\t\t * reach here. Fixup nr_scanned.\n1697:\t\t\t */\n1698:\t\t\tif (nr_pages \u003e 1)\n1699:\t\t\t\tsc-\u003enr_scanned -= (nr_pages - 1);\n1700:\tactivate_locked:\n1701:\t\t\tfolio_activate_locked(folio, stat);\n1702:\tkeep_locked:\n1703:\t\t\tfolio_unlock(folio);\n1704:\tkeep:\n1705:\t\t\tlist_add(\u0026folio-\u003elru, \u0026ret_folios);\n1706:\t\t\tVM_BUG_ON_FOLIO(folio_test_lru(folio) ||\n1707:\t\t\t\t\tfolio_test_unevictable(folio), folio);\n1708:\t\t}\n1709:\t\t/* 'folio_list' is always empty here */\n1710:\t\n1711:\t\t/* Migrate folios selected for demotion */\n1712:\t\tnr_demoted = demote_folio_list(\u0026demote_folios, pgdat, memcg);\n1713:\t\tnr_reclaimed += nr_demoted;\n1714:\t\tstat-\u003enr_demoted += nr_demoted;\n1715:\t\t/* Folios that could not be demoted are still in @demote_folios */\n1716:\t\tif (!list_empty(\u0026demote_folios)) {\n1717:\t\t\t/* Folios which weren't demoted go back on @folio_list */\n1718:\t\t\tlist_splice_init(\u0026demote_folios, folio_list);\n1719:\t\n"
} |
| 11/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 14308 output: 31 thoughts: 611 Thoughts: **Analyzing the Folio Activation Patch** Okay, let's break this down. First, this patch introduces `folio_activate_locked`. It's replacing the code block previously under `activate_locked:`, which immediately makes me think this is a critical section we need to understand. The first thing I'm noticing is the inclusion of assertions in `folio_activate_locked`. We have `VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);` and `VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);`. This is already a signal. We're replacing a `VM_BUG_ON_FOLIO(folio_test_active(folio), folio);` with a warning, and adding a warning for a locked folio. That's a definite change in error handling. It says something about the potential for errors, and a more graceful handling. Now, looking at `activate_locked_split:`, there's a clear change. Before, the code was clamping `nr_pages` to 1 if it was greater than 1, implying it came from `activate_locked_split`. Now, the code just updates `sc->nr_scanned` and calls `folio_activate_locked(folio, stat)`. This is where it gets interesting. Inside `folio_activate_locked`, it grabs the `nr_pages` using `folio_nr_pages(folio)`, and then updates the stats based on the *actual* number of pages in the folio. Hold on, wasn't there a potential bug with the `nr_pages` accounting if the folio was split? Ah, the comment in `folio_try_pageout` is relevant: "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." Okay, so the patch is taking advantage of this behavior and the change to use `folio_nr_pages` instead of a potentially stale `nr_pages` from `activate_locked_split`. That's a clever optimization and correct. But, I need to understand where `goto activate_locked_split;` is used. I'll need to grep for that in `mm/vmscan.c` to see the full picture and how it is being called now. The patch looks solid so far; I need to follow the full flow and make sure no regressions are introduced. |
| 12/2 | 2026/09/22 16:34 | tool | grepper |
0mArgs:{
"Expression": "activate_locked_split",
"PathPrefix": "mm/vmscan.c"
}Results: {
"Output": "mm/vmscan.c=1356=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1584-\t\t\t\tif (!folio_test_large(folio))\nmm/vmscan.c:1585:\t\t\t\t\tgoto activate_locked_split;\nmm/vmscan.c-1586-\t\t\t\tif (ret != -E2BIG)\n--\nmm/vmscan.c-1599-\t\t\t\tif (folio_alloc_swap(folio))\nmm/vmscan.c:1600:\t\t\t\t\tgoto activate_locked_split;\nmm/vmscan.c-1601-\t\t\t}\n--\nmm/vmscan.c-1692-\nmm/vmscan.c:1693:activate_locked_split:\nmm/vmscan.c-1694-\t\t/*\n"
} |
| 13/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 15733 output: 26 thoughts: 390 Thoughts: **My Assessment of this Patch** Okay, here we go, diving into some serious core memory management code! This is directly touching `mm/vmscan.c`, which means it's critical. Let's see... I'm looking at these guidelines, focusing on "Core Subsystems" and "Runtime Assertions and Defensive Checks" – both of which this patch seems to implicate. Specifically, it looks like this patch is modifying `shrink_folio_list()` and extracting and refactoring related functions: `folio_try_reclaim_free`, `folio_try_pageout`, `folio_try_unmap`, and `folio_activate_locked`. That's already raising a flag. And yes, I see it's altering runtime assertions; adding `VM_WARN_ON_ONCE_FOLIO` and changing a `VM_BUG_ON_FOLIO` to a `VM_WARN_ON_ONCE_FOLIO`. That's a definite red flag for fuzzing! It also has modifications to how `nr_pages` is handled when falling through `activate_locked_split` to `activate_locked` and changes return flow and local variable scoping (`mapping`, `nr_reclaimed`). The question is, is this reachable? Absolutely! `shrink_folio_list` is at the heart of memory reclaim. This code gets executed when there's memory pressure – kswapd runs, direct reclaim is triggered, memcg limits are hit... it's all over the place. So, *definitely* `WorthFuzzing` is `TRUE`. This is a prime target. Now, let's see about the configuration requirements. Where does this code even fit? I'll check `mm/vmscan.c` and `mm/Makefile` to see if there are any specific kernel configurations that must be enabled. I want to see how broadly this code is compiled and used. |
| 14/2 | 2026/09/22 16:34 | tool | grepper |
0mArgs:{
"Expression": "vmscan\\.o",
"PathPrefix": "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"
} |
| 15/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 16688 output: 28 thoughts: 86 Thoughts: Here's my analysis of the situation: **Investigating the Unconditional Inclusion of vmscan.o** Okay, so `vmscan.o` is being built unconditionally as part of the `mm/Makefile` – that's the starting point. I need to understand if there's any conditional compilation *within* the code that would impact its behavior or even make it effectively optional. The crucial question is, are there any config options that influence the internal workings of `shrink_folio_list` or any of the new helper functions that were introduced? Even though the object file is always *present*, specific kernel configurations could still effectively disable or significantly alter the code's behavior. The most direct way to check is to look for `#ifdef` directives. I need to be thorough. I'll focus on the area around the recent patch in `mm/vmscan.c`. I'll run a `grep` for `#ifdef` to see if any of the new logic or the existing surrounding functions are gated behind any configuration options. This should reveal the influence of kernel configuration on the inclusion of the new code, or on its impact if it is being compiled. |
| 16/2 | 2026/09/22 16:34 | tool | grepper |
0mArgs:{
"Expression": "#if",
"PathPrefix": "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=1356=static unsigned int shrink_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-1590-\t\t\t\t\tgoto activate_locked;\nmm/vmscan.c:1591:#ifdef CONFIG_TRANSPARENT_HUGEPAGE\nmm/vmscan.c-1592-\t\t\t\tif (nr_pages \u003e= HPAGE_PMD_NR) {\n--\nmm/vmscan.c=2846=static bool can_age_anon_pages(struct lruvec *lruvec,\n--\nmm/vmscan.c-2857-\nmm/vmscan.c:2858:#ifdef CONFIG_LRU_GEN\nmm/vmscan.c-2859-\nmm/vmscan.c=2860=DEFINE_STATIC_KEY_FALSE(lru_switch);\nmm/vmscan.c:2861:#ifdef CONFIG_LRU_GEN_ENABLED\nmm/vmscan.c-2862-DEFINE_STATIC_KEY_ARRAY_TRUE(lru_gen_caps, NR_LRU_GEN_CAPS);\n--\nmm/vmscan.c=2910=static struct lruvec *get_lruvec(struct mem_cgroup *memcg, int nid)\n--\nmm/vmscan.c-2913-\nmm/vmscan.c:2914:#ifdef CONFIG_MEMCG\nmm/vmscan.c-2915-\tif (memcg) {\n--\nmm/vmscan.c=3046=static void reset_bloom_filter(struct lru_gen_mm_state *mm_state, unsigned long seq)\n--\nmm/vmscan.c-3065-\nmm/vmscan.c:3066:#ifdef CONFIG_LRU_GEN_WALKS_MMU\nmm/vmscan.c-3067-\nmm/vmscan.c=3068=static struct lru_gen_mm_list *get_mm_list(struct mem_cgroup *memcg)\n--\nmm/vmscan.c-3074-\nmm/vmscan.c:3075:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3076-\tif (memcg)\n--\nmm/vmscan.c=3108=void lru_gen_add_mm(struct mm_struct *mm)\n--\nmm/vmscan.c-3114-\tVM_WARN_ON_ONCE(!list_empty(\u0026mm-\u003elru_gen.list));\nmm/vmscan.c:3115:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3116-\tVM_WARN_ON_ONCE(mm-\u003elru_gen.memcg);\n--\nmm/vmscan.c=3135=void lru_gen_del_mm(struct mm_struct *mm)\n--\nmm/vmscan.c-3143-\nmm/vmscan.c:3144:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3145-\tmemcg = mm-\u003elru_gen.memcg;\n--\nmm/vmscan.c-3167-\nmm/vmscan.c:3168:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3169-\tmem_cgroup_put(mm-\u003elru_gen.memcg);\n--\nmm/vmscan.c-3173-\nmm/vmscan.c:3174:#ifdef CONFIG_MEMCG\nmm/vmscan.c-3175-void lru_gen_migrate_mm(struct mm_struct *mm)\n--\nmm/vmscan.c=4606=static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)\n--\nmm/vmscan.c-4649-\nmm/vmscan.c:4650:#ifdef CONFIG_MEMCG\nmm/vmscan.c-4651-\n--\nmm/vmscan.c=5862=static int lru_gen_seq_show(struct seq_file *m, void *v)\n--\nmm/vmscan.c-5875-\nmm/vmscan.c:5876:#ifdef CONFIG_MEMCG\nmm/vmscan.c-5877-\t\tif (memcg)\n--\nmm/vmscan.c=6131=void lru_gen_init_lruvec(struct lruvec *lruvec)\n--\nmm/vmscan.c-6150-\nmm/vmscan.c:6151:#ifdef CONFIG_MEMCG\nmm/vmscan.c-6152-\n--\nmm/vmscan.c=7009=unsigned long try_to_free_pages(struct zonelist *zonelist, int order,\n--\nmm/vmscan.c-7051-\nmm/vmscan.c:7052:#ifdef CONFIG_MEMCG\nmm/vmscan.c-7053-\n--\nmm/vmscan.c=7837=bool kswapd_test_hopeless(pg_data_t *pgdat)\n--\nmm/vmscan.c-7841-\nmm/vmscan.c:7842:#ifdef CONFIG_HIBERNATION\nmm/vmscan.c-7843-/*\n--\nmm/vmscan.c=7922=static const struct ctl_table vmscan_sysctl_table[] = {\n--\nmm/vmscan.c-7931-\t},\nmm/vmscan.c:7932:#ifdef CONFIG_NUMA\nmm/vmscan.c-7933-\t{\n--\nmm/vmscan.c=7954=module_init(kswapd_init)\nmm/vmscan.c-7955-\nmm/vmscan.c:7956:#ifdef CONFIG_NUMA\nmm/vmscan.c-7957-/*\n--\nmm/vmscan.c=8299=EXPORT_SYMBOL_GPL(check_move_unevictable_folios);\nmm/vmscan.c-8300-\nmm/vmscan.c:8301:#if defined(CONFIG_SYSFS) \u0026\u0026 defined(CONFIG_NUMA)\nmm/vmscan.c-8302-static ssize_t reclaim_store(struct device *dev,\n"
} |
| 17/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 19050 output: 27 thoughts: 181 Thoughts: **My Initial Assessment of the Code** Okay, so I'm looking at this new code, and the first thing that jumps out is that it isn't conditionally compiled with an `#ifdef`. That's unusual, and it immediately makes me start to think about dependencies. I need to figure out if it relies on any specific kernel configurations being enabled. Are we dealing with `CONFIG_SWAP` or `CONFIG_MEMCG`? Let's see...I'll check some of those relevant functions. Right, things like `count_memcg_folio_events`, `mem_cgroup_swap_full`, or `free_unref_folios`. I seem to recall those having stub definitions if `CONFIG_MEMCG` or `CONFIG_SWAP` are disabled, which would be a huge clue. But, in any normal kernel config, and certainly in a syzkaller context, those are almost always enabled. It's rare to see them disabled. Hmm, maybe there's a more subtle dependency? I should check and see if there are any specific configs that are *required* to actually reach or enable this section of code. I need to dig deeper. Hold on...this is an interesting thought... does `shrink_folio_list` get called if `CONFIG_LRU_GEN_ENABLED` is on? That's a good question! I need to investigate that relationship. Yes, that's a very interesting question. Okay, time to check where `shrink_folio_list()` is actually *called*. That's the next logical step. I need to trace its usage. |
| 18/2 | 2026/09/22 16:34 | tool | grepper |
0mArgs:{
"Expression": "shrink_folio_list",
"PathPrefix": "mm/"
}Results: {
"Output": "mm/memory.c=5606=static vm_fault_t __do_fault(struct vm_fault *vmf)\n--\nmm/memory.c-5620-\t * pte_alloc_one\nmm/memory.c:5621:\t * shrink_folio_list\nmm/memory.c-5622-\t * folio_wait_writeback(A)\n--\nmm/shmem.c=1810=int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,\n--\nmm/shmem.c-1944-\t\t * The swap_cache_del_folio() below could be left for\nmm/shmem.c:1945:\t\t * shrink_folio_list()'s folio_free_swap() to dispose of;\nmm/shmem.c-1946-\t\t * but I'm a little nervous about letting this folio out of\n--\nmm/swap_state.c=33=static const int page_cluster_max = 31;\n--\nmm/swap_state.c-36- * swapper_space is a fiction, retained to simplify the path through\nmm/swap_state.c:37: * vmscan's shrink_folio_list.\nmm/swap_state.c-38- */\n--\nmm/truncate.c=606=static int folio_launder(struct address_space *mapping, struct folio *folio)\n--\nmm/truncate.c-618- * invalidation guarantees, and cannot afford to leave folios behind because\nmm/truncate.c:619: * shrink_folio_list() has a temp ref on them, or because they're transiently\nmm/truncate.c-620- * sitting in the folio_add_lru() caches.\n--\nmm/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=1321=static bool folio_try_unmap(struct folio *folio, struct reclaim_stat *stat,\n--\nmm/vmscan.c-1355- */\nmm/vmscan.c:1356:static unsigned int shrink_folio_list(struct list_head *folio_list,\nmm/vmscan.c-1357-\t\tstruct pglist_data *pgdat, struct scan_control *sc,\n--\nmm/vmscan.c=1755=unsigned int reclaim_clean_pages_from_list(struct zone *zone,\n--\nmm/vmscan.c-1785-\tnoreclaim_flag = memalloc_noreclaim_save();\nmm/vmscan.c:1786:\tnr_reclaimed = shrink_folio_list(\u0026clean_folios, zone-\u003ezone_pgdat, \u0026sc,\nmm/vmscan.c-1787-\t\t\t\t\t\u0026stat, true, NULL);\n--\nmm/vmscan.c=2107=static void handle_reclaim_writeback(unsigned long nr_taken,\n--\nmm/vmscan.c-2127-\t\t * the kernel flusher here and later waiting on folios\nmm/vmscan.c:2128:\t\t * which are in writeback to finish (see shrink_folio_list()).\nmm/vmscan.c-2129-\t\t *\n--\nmm/vmscan.c=2149=static unsigned long shrink_inactive_list(unsigned long nr_to_scan,\n--\nmm/vmscan.c-2192-\nmm/vmscan.c:2193:\tnr_reclaimed = shrink_folio_list(\u0026folio_list, pgdat, sc, \u0026stat, false,\nmm/vmscan.c-2194-\t\t\t\t\t lruvec_memcg(lruvec));\n--\nmm/vmscan.c=2320=static unsigned int reclaim_folio_list(struct list_head *folio_list,\n--\nmm/vmscan.c-2333-\nmm/vmscan.c:2334:\tnr_reclaimed = shrink_folio_list(folio_list, pgdat, \u0026sc, \u0026stat, true, NULL);\nmm/vmscan.c-2335-\twhile (!list_empty(folio_list)) {\n--\nmm/vmscan.c=4437=static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)\n--\nmm/vmscan.c-4477-/*\nmm/vmscan.c:4478: * This function exploits spatial locality when shrink_folio_list() walks the\nmm/vmscan.c-4479- * rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages. If\n--\nmm/vmscan.c=5106=static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,\n--\nmm/vmscan.c-5140-retry:\nmm/vmscan.c:5141:\treclaimed = shrink_folio_list(\u0026list, pgdat, sc, \u0026stat, false, memcg);\nmm/vmscan.c-5142-\tsc-\u003enr_reclaimed += reclaimed;\n"
} |
| 19/2 | 2026/09/22 16:34 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 21023 output: 191 thoughts: 2852 Thoughts: **Folio Reclamation Refactor Summary** Alright, let's break this down. From what I see, `shrink_folio_list()` is the linchpin here, called from all the main folio reclaim paths: traditional LRU, MGLRU, compaction, migration, the works. It's the central function in the Linux kernel for reclaiming memory via folios. Given that it's called from so many critical areas, it needs thorough testing. Now, looking at the introduced and modified functions, it's clear the core logic is being refactored, split into modular functions: `folio_try_reclaim_free`, `folio_try_pageout`, `folio_try_unmap`, and `folio_activate_locked`. These are all static functions within `mm/vmscan.c`. Since they're not static inline functions in headers, they have distinct symbols, and the compiler almost certainly won't inline the large `shrink_folio_list`. This is key. These functions *directly* implement the altered logic. Crucially, `shrink_folio_list()` is NOT a ubiquitous function. It's specific to the memory reclaim subsystem, so it is a good focus. It is called only when memory is under pressure or explicitly via reclaim paths, unlike general memory allocation, which is ubiquitous. There are no config flags required to *reach* the modified code. `mm/vmscan.c` is compiled into the kernel unconditionally (unless you count `CONFIG_MMU` which is standard on amd64 or `CONFIG_SWAP` for the swap paths), so we don't have to worry about `#ifdef` guards. Now, let's get into the nitty-gritty. There are a few interesting changes here, and potential issues: 1. In `folio_activate_locked`, the change to how `nr_pages` is computed, along with a new assertion, `VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio)`, makes me double-check the locking state and accounting. The previous assumption that the `nr_pages` was reset during activation isn't valid anymore. 2. `folio_try_reclaim_free()` now has an interesting local mapping, meaning that the mapping could be stale. 3. `folio_try_pageout()` also now has new checks. These are significant refactors of the core memory reclaim logic with new assertions and changed accounting. Any fuzzing effort should really target the whole set of functions. Based on the nature of these changes, and their centrality to the reclaim process, the functions that are going to be in FocusSymbols are: * `shrink_folio_list` * `folio_try_reclaim_free` * `folio_try_pageout` * `folio_try_unmap` * `folio_activate_locked` These are the core functions implementing the refactored folio reclamation logic. They aren't ubiquitous, they are specific to the subsystem. The code is fully reachable during page reclaim. This warrants fuzzing. |
| 20/2 | 2026/09/22 16:34 | tool | set-results |
0mArgs:{
"EnableConfigs": [],
"FocusSymbols": [
"shrink_folio_list",
"folio_try_reclaim_free",
"folio_try_pageout",
"folio_try_unmap",
"folio_activate_locked"
],
"Reasoning": "The patch refactors the core page reclamation routine shrink_folio_list() in mm/vmscan.c into several helper functions (folio_activate_locked, folio_try_reclaim_free, folio_try_pageout, and folio_try_unmap). It alters state accounting and handling during folio splitting and pageout, and introduces new runtime assertions (such as VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio)). This is reachable core memory management code executed under memory pressure and warrants fuzzing.",
"WorthFuzzing": true
}Results: {
"EnableConfigs": null,
"FocusSymbols": [
"shrink_folio_list",
"folio_try_reclaim_free",
"folio_try_pageout",
"folio_try_unmap",
"folio_activate_locked"
],
"Reasoning": "The patch refactors the core page reclamation routine shrink_folio_list() in mm/vmscan.c into several helper functions (folio_activate_locked, folio_try_reclaim_free, folio_try_pageout, and folio_try_unmap). It alters state accounting and handling during folio splitting and pageout, and introduces new runtime assertions (such as VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio)). This is reachable core memory management code executed under memory pressure and warrants fuzzing.",
"WorthFuzzing": true
} |
| 21/1 | 2026/09/22 16:34 | action | If |
0mArgs:{
"WorthFuzzing": true
}Results: null |
| 22/2 | 2026/09/22 16:34 | agent | kmsan-evaluator |
0mModel:core Args: null Results: {
"KMSANReasoning": "The patch is a refactoring of the folio reclamation loop in `shrink_folio_list()` (`mm/vmscan.c`). It extracts monolithic blocks of code into smaller helper functions: `folio_activate_locked()`, `folio_try_reclaim_free()`, `folio_try_pageout()`, and `folio_try_unmap()`.\n\nNo new data structures, stack/heap allocations, or copies to user space (such as copy_to_user or netlink/ioctl transfers) are introduced. All local variables and pointers are properly initialized, and no uninitialized memory paths or info-leaks are created or exposed. Any potential regressions or bugs from this refactoring (e.g., refcounting issues, lock handling, or use-after-free) would be detected by standard debugging facilities (KASAN, page-refcount checks, and lockdep), making a dedicated KMSAN fuzzing session unnecessary.",
"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 7be148f91d6dd00d1d9ac102004804b1e9a3e38e
Author: syz-cluster <triage@syzkaller.com>
Date: Tue Sep 22 16:33:06 2026 +0000
syz-cluster: applied patch under review
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e200ce3eb056b..71b507011603d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1155,8 +1155,203 @@ 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);
+ }
+}
+
+enum folio_reclaim_result {
+ FOLIO_RECLAIM_KEEP,
+ FOLIO_RECLAIM_ACTIVATE,
+ FOLIO_RECLAIM_SUCCESS,
+};
+
+static enum folio_reclaim_result folio_try_reclaim_free(struct folio *folio,
+ struct folio_batch *free_folios,
+ struct scan_control *sc,
+ unsigned int *nr_reclaimed)
+{
+ 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.
+ */
+ *nr_reclaimed += nr_pages;
+ return FOLIO_RECLAIM_SUCCESS;
+ }
+ }
+
+ 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);
+ *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);
+ }
+ return FOLIO_RECLAIM_SUCCESS;
+}
+
+enum folio_pageout_result {
+ FOLIO_PAGEOUT_KEEP_LOCKED,
+ FOLIO_PAGEOUT_KEEP_UNLOCKED,
+ FOLIO_PAGEOUT_ACTIVATE,
+ FOLIO_PAGEOUT_FREE, /* folio is locked, hand it to folio_try_reclaim_free() */
+};
+
+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 *mapping = folio_mapping(folio);
+ 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_FREE;
+ }
+ unreachable();
+}
+
+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;
+}
+
/*
- * shrink_folio_list() returns the number of reclaimed pages
+ * 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,
@@ -1433,36 +1628,9 @@ 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 +1642,6 @@ 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)) {
/*
@@ -1495,152 +1662,43 @@ 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.
*/
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;
- }
+ switch (folio_try_pageout(folio, sc, &ctx, folio_list)) {
+ case FOLIO_PAGEOUT_ACTIVATE:
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;
- }
+ case FOLIO_PAGEOUT_KEEP_LOCKED:
+ goto keep_locked;
+ case FOLIO_PAGEOUT_KEEP_UNLOCKED:
+ goto keep;
+ case FOLIO_PAGEOUT_FREE:
+ break; /* folio is locked; try to free it below */
}
}
- 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, &free_folios, sc,
+ &nr_reclaimed)) {
+ 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_SUCCESS:
+ 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:
|
| 23/3 | 2026/09/22 16:34 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 6936 output: 221 thoughts: 1439 Thoughts: **KMSAN Evaluation: Patch in `mm/vmscan.c` Refactoring** Alright, let's dissect this patch and decide if we need a KMSAN fuzzing session. The patch is touching `mm/vmscan.c`, which always warrants careful scrutiny. It looks like we're refactoring `shrink_folio_list`. The core of the change is breaking this large function into several helper functions: `folio_activate_locked`, `folio_try_reclaim_free`, `folio_try_pageout`, and `folio_try_unmap`. Okay, so this is about code organization, but we need to verify there are *no* hidden dangers. First, let's compare `shrink_folio_list` before and after. My primary concerns are around: new allocations, any data copied to user space, the introduction of uninitialized memory, potential information leaks, or issues related to structure padding. Let's dig into each of these newly extracted functions. 1. `folio_activate_locked` handles folio activation and associated accounting. The code looks very similar to existing logic in the original function (the `activate_locked:` label), including checks for active folios and handling swap cache entries. It uses `VM_WARN_ON_ONCE_FOLIO` which is a good sign for sanity checks. All variables are initialized. No new risks appear here. 2. `folio_try_reclaim_free` replaces the freeing and unmapping logic at the bottom of the loop in `shrink_folio_list`. It deals with the freeing of folios, batching, and deferred unmapping. It's a key part of the reclaim process. I'm checking for anything new that is missed. Local variable `nr_reclaimed` is passed by pointer from `shrink_folio_list`, but it was already initialized in the original function. The function's logic seems safe. 3. `folio_try_pageout` calls `pageout`, which is a well-established function. It's about handling pageout operations and returns a pageout result. This is a crucial section, but my initial impression is that the new function is merely a better structure of existing calls. Everything seems initialized. 4. `folio_try_unmap` deals with unmapping folios. Checks for TTU flags and calls `try_to_unmap`. Again, checking everything carefully... and the variables initialized (`enum ttu_flags flags`, `bool was_swapbacked`). Okay, no new data copied to user space, good. Regarding uninitialized variables or memory, it appears that all local variables within `shrink_folio_list` and the new functions are properly initialized before use. The code uses existing data structures. It doesn't introduce any new stack or heap allocations that would cause me to worry. The patch is purely about simplifying and restructuring the folio reclaim logic. Now, let's double-check the KMSAN rules. We only need KMSAN if the patch introduces or modifies kernel structures sent to user space (nope), conditional logic dependent on uninitialized variables (nope), allocation/initialization of complex data structures where uninitialized fields are read (nope), or allows access to uninitialized bytes of existing buffers (nope). This patch is just refactoring the core memory management to break down a long monolithic loop into more manageable functions. It seems very low risk from a KMSAN perspective. No new uninitialized memory exposure. All clear. No KMSAN needed here. Therefore, `NeedsKMSAN = false`. I'll run the `set-results` tool and provide this reasoning. |
| 24/3 | 2026/09/22 16:35 | tool | set-results |
0mArgs:{
"KMSANReasoning": "The patch is a refactoring of the folio reclamation loop in `shrink_folio_list()` (`mm/vmscan.c`). It extracts monolithic blocks of code into smaller helper functions: `folio_activate_locked()`, `folio_try_reclaim_free()`, `folio_try_pageout()`, and `folio_try_unmap()`.\n\nNo new data structures, stack/heap allocations, or copies to user space (such as copy_to_user or netlink/ioctl transfers) are introduced. All local variables and pointers are properly initialized, and no uninitialized memory paths or info-leaks are created or exposed. Any potential regressions or bugs from this refactoring (e.g., refcounting issues, lock handling, or use-after-free) would be detected by standard debugging facilities (KASAN, page-refcount checks, and lockdep), making a dedicated KMSAN fuzzing session unnecessary.",
"NeedsKMSAN": false
}Results: {
"KMSANReasoning": "The patch is a refactoring of the folio reclamation loop in `shrink_folio_list()` (`mm/vmscan.c`). It extracts monolithic blocks of code into smaller helper functions: `folio_activate_locked()`, `folio_try_reclaim_free()`, `folio_try_pageout()`, and `folio_try_unmap()`.\n\nNo new data structures, stack/heap allocations, or copies to user space (such as copy_to_user or netlink/ioctl transfers) are introduced. All local variables and pointers are properly initialized, and no uninitialized memory paths or info-leaks are created or exposed. Any potential regressions or bugs from this refactoring (e.g., refcounting issues, lock handling, or use-after-free) would be detected by standard debugging facilities (KASAN, page-refcount checks, and lockdep), making a dedicated KMSAN fuzzing session unnecessary.",
"NeedsKMSAN": false
} |
| Total Calls | Total Tokens | Avg Tokens | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|
| Total Calls | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|