After the changes of the prior commits, page/folio->private != NULL is now equivalent to checking PG_private.
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. folio_set/clear_private() and Set/ClearPagePrivate() become no-ops. PG_private is no longer checked at page free time. KPF_PRIVATE exposes PG_private to userspace. Change its code logic to check folio->private != NULL and exclude non-pagecache, swapcache, hugetlb, and anon folios. One minor semantic change, for orphaned pagecache folios (mapping == NULL) with fs-private data will no longer have KPF_PRIVATE. Assisted-by: Claude:claude-opus-4-8 Assisted-by: Codex:gpt-5 Signed-off-by: Zi Yan <[email protected]> To: Andrew Morton <[email protected]> To: David Hildenbrand <[email protected]> To: Steven Rostedt <[email protected]> To: Masami Hiramatsu <[email protected]> To: Lorenzo Stoakes <[email protected]> To: "Matthew Wilcox (Oracle)" <[email protected]> To: Jan Kara <[email protected]> To: Johannes Weiner <[email protected]> Cc: "Liam R. Howlett" <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: Mike Rapoport <[email protected]> Cc: Suren Baghdasaryan <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Mathieu Desnoyers <[email protected]> Cc: Zi Yan <[email protected]> Cc: Baolin Wang <[email protected]> Cc: Nico Pache <[email protected]> Cc: Ryan Roberts <[email protected]> Cc: Dev Jain <[email protected]> Cc: Barry Song <[email protected]> Cc: Lance Yang <[email protected]> Cc: Usama Arif <[email protected]> Cc: Matthew Brost <[email protected]> Cc: Joshua Hahn <[email protected]> Cc: Rakie Kim <[email protected]> Cc: Byungchul Park <[email protected]> Cc: Gregory Price <[email protected]> Cc: Ying Huang <[email protected]> Cc: Alistair Popple <[email protected]> Cc: Qi Zheng <[email protected]> Cc: Shakeel Butt <[email protected]> Cc: Kairui Song <[email protected]> Cc: Axel Rasmussen <[email protected]> Cc: Yuanchu Xie <[email protected]> Cc: Wei Xu <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] --- fs/proc/page.c | 6 +++++- include/linux/mm.h | 11 ++++++----- include/linux/page-flags.h | 26 +++++++++++++++++++++----- include/trace/events/pagemap.h | 4 +++- mm/huge_memory.c | 4 +++- mm/migrate.c | 3 ++- mm/page-writeback.c | 5 ++++- mm/vmscan.c | 3 ++- 8 files changed, 46 insertions(+), 16 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 260772b20bd99..abfa6f7d890cc 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -232,7 +232,11 @@ 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); + /* preserve the original KPF_PRIVATE semantics by excluding non pagecache folios */ + if (folio->mapping && !folio_test_anon(folio) && + (folio_get_private(folio) && !folio_test_swapcache(folio) && + !folio_test_hugetlb(folio))) + u |= BIT_ULL(KPF_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/mm.h b/include/linux/mm.h index 7fabe6c66b4b7..ebc035ac26ccc 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2961,9 +2961,9 @@ 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), @@ -3003,8 +3003,9 @@ static inline int folio_expected_ref_count(const struct folio *folio) 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 from filesystem private data. */ + ref_count += !!folio->private && !folio_test_hugetlb(folio) && + !folio_test_swapcache(folio); } /* One reference per page table mapping. */ diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 7a863572adce7..8efc61f967302 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(page); +} + +/* 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_swapcache(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..fb9abec40ec79 100644 --- a/include/trace/events/pagemap.h +++ b/include/trace/events/pagemap.h @@ -22,7 +22,9 @@ (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) \ + (folio_test_private(folio) && \ + !folio_test_swapcache(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 21c92ee48e469..d21a9b8f40d15 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -4799,7 +4799,9 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start, * will try to drop it before split and then check if the folio * can be split or not. So skip the check here. */ - if (!folio_test_private(folio) && + if (!(folio_test_private(folio) && + !folio_test_swapcache(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 b937cbd764808..ad5daef8721cf 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1330,7 +1330,8 @@ 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_swapcache(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 47495be68598f..b44468383f900 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -2706,7 +2706,10 @@ 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)); + __folio_mark_dirty(folio, mapping, + !(folio_test_private(folio) && + !folio_test_swapcache(folio) && + !folio_test_hugetlb(folio))); if (mapping->host) { /* !PageAnon && !swapper_space */ diff --git a/mm/vmscan.c b/mm/vmscan.c index 17d2b793cbfc4..ab059a2c6ea35 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -954,7 +954,8 @@ 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_swapcache(folio) && + !folio_test_hugetlb(folio))) return; mapping = folio_mapping(folio); -- 2.53.0
