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Stop checking PG_private on pages and folios and use page/folio->private instead, except swapcache and hugetlb folios, because the former uses a field (swp_entry_t swap) overlapping with ->private and the latter sets its flags in ->private. Exclude swapcache and hugetlb when the code is meant to check PG_private only. PG_swapcache and folio->swap.val cannot be set/clear as a whole, so excluding swapcache with folio_test_swapcache() is not reliable. Instead, use folio_test_swapbacked(), since PG_swapbacked is stable when a folio is added to/removed from swapcache. folio_expected_ref_count() can be called without folio lock, so annotate folio_test_private() with data_race() to avoid triggering race condition checks. While at it, annotate folio->mapping too. Add data_race() annotation for other lockless callers too. folio_set/clear_private() and Set/ClearPagePrivate() become no-ops. PG_private is no longer checked at page free time. Remove KPF_PRIVATE since PG_private is no longer used. Assisted-by: Claude:claude-opus-4-8 Assisted-by: Codex:gpt-5 Signed-off-by: Zi Yan To: Andrew Morton To: David Hildenbrand To: Steven Rostedt To: Masami Hiramatsu To: Lorenzo Stoakes To: "Matthew Wilcox (Oracle)" To: Jan Kara To: Johannes Weiner Cc: "Liam R. Howlett" Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Mathieu Desnoyers Cc: Zi Yan Cc: Baolin Wang Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Matthew Brost Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Qi Zheng Cc: Shakeel Butt Cc: Kairui Song Cc: Axel Rasmussen Cc: Yuanchu Xie Cc: Wei Xu Cc: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-trace-kernel@vger.kernel.org --- fs/proc/page.c | 1 - include/linux/kernel-page-flags.h | 1 - include/linux/mm.h | 22 +++++++++++++++------- include/linux/page-flags.h | 26 +++++++++++++++++++++----- include/trace/events/pagemap.h | 5 ++++- mm/huge_memory.c | 5 ++++- mm/migrate.c | 3 ++- mm/page-writeback.c | 6 +++++- mm/vmscan.c | 3 ++- tools/mm/page-types.c | 2 -- 10 files changed, 53 insertions(+), 21 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 260772b20bd99..f90e1030825e9 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -232,7 +232,6 @@ u64 stable_page_flags(const struct page *page) u |= kpf_copy_bit(k, KPF_RESERVED, PG_reserved); u |= kpf_copy_bit(k, KPF_OWNER_2, PG_owner_2); - u |= kpf_copy_bit(k, KPF_PRIVATE, PG_private); u |= kpf_copy_bit(k, KPF_PRIVATE_2, PG_private_2); u |= kpf_copy_bit(k, KPF_OWNER_PRIVATE, PG_owner_priv_1); u |= kpf_copy_bit(k, KPF_ARCH, PG_arch_1); diff --git a/include/linux/kernel-page-flags.h b/include/linux/kernel-page-flags.h index 196778a087c4d..fe5ab6e50bd70 100644 --- a/include/linux/kernel-page-flags.h +++ b/include/linux/kernel-page-flags.h @@ -11,7 +11,6 @@ #define KPF_RESERVED 32 #define KPF_MLOCKED 33 #define KPF_OWNER_2 34 -#define KPF_PRIVATE 35 #define KPF_PRIVATE_2 36 #define KPF_OWNER_PRIVATE 37 #define KPF_ARCH 38 diff --git a/include/linux/mm.h b/include/linux/mm.h index c49ef99b4413b..5eb8a62fafb56 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3004,9 +3004,9 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio) * @folio: the folio * * Calculate the expected folio refcount, taking references from the pagecache, - * swapcache, PG_private and page table mappings into account. Useful in - * combination with folio_ref_count() to detect unexpected references (e.g., - * GUP or other temporary references). + * swapcache, private data (folio->private != NULL) and page table mappings into + * account. Useful in combination with folio_ref_count() to detect unexpected + * references (e.g., GUP or other temporary references). * * Does currently not consider references from the LRU cache. If the folio * was isolated from the LRU (which is the case during migration or split), @@ -3044,10 +3044,18 @@ static inline int folio_expected_ref_count(const struct folio *folio) ref_count += folio_test_swapcache(folio) << order; if (!folio_test_anon(folio)) { - /* One reference per page from the pagecache. */ - ref_count += !!folio->mapping << order; - /* One reference from PG_private. */ - ref_count += folio_test_private(folio); + /* + * One reference per page from the pagecache. + * Use data_race() since folio might not be locked. + */ + ref_count += !!data_race(folio->mapping) << order; + /* + * One reference from filesystem private data. + * Use data_race() since folio might not be locked. + */ + ref_count += data_race(folio_test_private(folio)) && + !folio_test_hugetlb(folio) && + !folio_test_swapbacked(folio); } /* One reference per page table mapping. */ diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 86dd0470da117..9cb4d64739798 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -578,7 +578,23 @@ FOLIO_FLAG(swapbacked, FOLIO_HEAD_PAGE) * for its own purposes. * - PG_private and PG_private_2 cause release_folio() and co to be invoked */ -PAGEFLAG(Private, private, PF_ANY) + +static __always_inline bool folio_test_private(const struct folio *folio) +{ + return folio->private; +} + +static __always_inline int PagePrivate(const struct page *page) +{ + return !!page->private; +} + +/* no-ops during transition */ +static __always_inline void folio_set_private(struct folio *folio) { } +static __always_inline void folio_clear_private(struct folio *folio) { } +static __always_inline void SetPagePrivate(struct page *page) { } +static __always_inline void ClearPagePrivate(struct page *page) { } + FOLIO_FLAG(private_2, FOLIO_HEAD_PAGE) /* owner_2 can be set on tail pages for anon memory */ @@ -1170,7 +1186,7 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) */ #define PAGE_FLAGS_CHECK_AT_FREE \ (1UL << PG_lru | 1UL << PG_locked | \ - 1UL << PG_private | 1UL << PG_private_2 | \ + 1UL << PG_private_2 | \ 1UL << PG_writeback | 1UL << PG_reserved | \ 1UL << PG_active | \ 1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK) @@ -1194,8 +1210,6 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) (0xffUL /* order */ | 1UL << PG_has_hwpoisoned | \ 1UL << PG_large_rmappable | 1UL << PG_partially_mapped) -#define PAGE_FLAGS_PRIVATE \ - (1UL << PG_private | 1UL << PG_private_2) /** * folio_has_private - Determine if folio has private stuff * @folio: The folio to be checked @@ -1205,7 +1219,9 @@ static __always_inline void __ClearPageAnonExclusive(struct page *page) */ static inline int folio_has_private(const struct folio *folio) { - return !!(folio->flags.f & PAGE_FLAGS_PRIVATE); + return (!!folio->private && !folio_test_swapbacked(folio) && + !folio_test_hugetlb(folio)) || + folio_test_private_2(folio); } #undef PF_ANY diff --git a/include/trace/events/pagemap.h b/include/trace/events/pagemap.h index 36c3a90f0acca..8193f91216822 100644 --- a/include/trace/events/pagemap.h +++ b/include/trace/events/pagemap.h @@ -22,7 +22,10 @@ (folio_test_swapcache(folio) ? PAGEMAP_SWAPCACHE : 0) | \ (folio_test_swapbacked(folio) ? PAGEMAP_SWAPBACKED : 0) | \ (folio_test_mappedtodisk(folio) ? PAGEMAP_MAPPEDDISK : 0) | \ - (folio_test_private(folio) ? PAGEMAP_BUFFERS : 0) \ + /* data_race() is used to read folio->private locklessly */ \ + (data_race(folio_test_private(folio)) && \ + !folio_test_swapbacked(folio) && \ + !folio_test_hugetlb(folio) ? PAGEMAP_BUFFERS : 0) \ ) TRACE_EVENT(mm_lru_insertion, diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d1ce061601bcd..9b2a9d0794a61 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -4831,8 +4831,11 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start, * For folios with private, split_huge_page_to_list_to_order() * will try to drop it before split and then check if the folio * can be split or not. So skip the check here. + * data_race() is used to read folio->private locklessly. */ - if (!folio_test_private(folio) && + if (!(data_race(folio_test_private(folio)) && + !folio_test_swapbacked(folio) && + !folio_test_hugetlb(folio)) && folio_expected_ref_count(folio) != folio_ref_count(folio)) goto next; diff --git a/mm/migrate.c b/mm/migrate.c index a369d0c95c386..f6befd3ff1c46 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1327,7 +1327,8 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, * free the metadata, so the page can be freed. */ if (!src->mapping) { - if (folio_test_private(src)) { + if (folio_test_private(src) && !folio_test_swapbacked(src) && + !folio_test_hugetlb(src)) { try_to_free_buffers(src); goto out; } diff --git a/mm/page-writeback.c b/mm/page-writeback.c index eeab25d6ce364..02ad49b10be07 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -2705,7 +2705,11 @@ bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio) if (folio_test_set_dirty(folio)) return false; - __folio_mark_dirty(folio, mapping, !folio_test_private(folio)); + /* data_race() is used to read folio->private locklessly */ + __folio_mark_dirty(folio, mapping, + !(data_race(folio_test_private(folio)) && + !folio_test_swapbacked(folio) && + !folio_test_hugetlb(folio))); if (mapping->host) { /* !PageAnon && !swapper_space */ diff --git a/mm/vmscan.c b/mm/vmscan.c index 40d3f1b48a74c..9348ebf9de882 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -978,7 +978,8 @@ static void folio_check_dirty_writeback(struct folio *folio, *writeback = folio_test_writeback(folio); /* Verify dirty/writeback state if the filesystem supports it */ - if (!folio_test_private(folio)) + if (!(folio_test_private(folio) && !folio_test_swapbacked(folio) && + !folio_test_hugetlb(folio))) return; mapping = folio_mapping(folio); diff --git a/tools/mm/page-types.c b/tools/mm/page-types.c index 7fc5a8be5997f..47e4781c5fc38 100644 --- a/tools/mm/page-types.c +++ b/tools/mm/page-types.c @@ -73,7 +73,6 @@ #define KPF_RESERVED 32 #define KPF_MLOCKED 33 #define KPF_OWNER_2 34 -#define KPF_PRIVATE 35 #define KPF_PRIVATE_2 36 #define KPF_OWNER_PRIVATE 37 #define KPF_ARCH 38 @@ -131,7 +130,6 @@ static const char * const page_flag_names[] = { [KPF_RESERVED] = "r:reserved", [KPF_MLOCKED] = "m:mlocked", [KPF_OWNER_2] = "d:owner_2", - [KPF_PRIVATE] = "P:private", [KPF_PRIVATE_2] = "p:private_2", [KPF_OWNER_PRIVATE] = "O:owner_private", [KPF_ARCH] = "h:arch", -- 2.53.0