From 4996fc547f5b49f4a43c261dfadb02cf165cdb51 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Mon, 3 Mar 2025 17:29:56 +0100 Subject: [PATCH] mm: let _folio_nr_pages overlay memcg_data in first tail page Let's free up some more of the "unconditionally available on 64BIT" space in order-1 folios by letting _folio_nr_pages overlay memcg_data in the first tail page (second folio page). Consequently, we have the optimization now whenever we have CONFIG_MEMCG, independent of 64BIT. We have to make sure that page->memcg on tail pages does not return "surprises". page_memcg_check() already properly refuses PageTail(). Let's do that earlier in print_page_owner_memcg() to avoid printing wrong "Slab cache page" information. No other code should touch that field on tail pages of compound pages. Reset the "_nr_pages" to 0 when splitting folios, or when freeing them back to the buddy (to avoid false page->memcg_data "bad page" reports). Note that in __split_huge_page(), folio_nr_pages() would stop working already as soon as we start messing with the subpages. Most kernel configs should have at least CONFIG_MEMCG enabled, even if disabled at runtime. 64byte "struct memmap" is what we usually have on 64BIT. While at it, rename "_folio_nr_pages" to "_nr_pages". Hopefully memdescs / dynamically allocating "strut folio" in the future will further clean this up, e.g., making _nr_pages available in all configs and maybe even in small folios. Doing that should be fairly easy on top of this change. [david@redhat.com: make "make htmldoc" happy] Link: https://lkml.kernel.org/r/a97f8a91-ec41-4796-81e3-7c9e0e491ba4@redhat.com Link: https://lkml.kernel.org/r/20250303163014.1128035-4-david@redhat.com Signed-off-by: David Hildenbrand Reviewed-by: Kirill A. Shutemov Cc: Andy Lutomirks^H^Hski Cc: Borislav Betkov Cc: Dave Hansen Cc: Ingo Molnar Cc: Jann Horn Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Lance Yang Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcow (Oracle) Cc: Michal Koutn Cc: Muchun Song Cc: tejun heo Cc: Thomas Gleixner Cc: Vlastimil Babka Cc: Zefan Li Signed-off-by: Andrew Morton --- include/linux/mm.h | 4 ++-- include/linux/mm_types.h | 32 ++++++++++++++++++++++++-------- mm/huge_memory.c | 8 ++++++++ mm/internal.h | 4 ++-- mm/page_alloc.c | 6 +++++- mm/page_owner.c | 2 +- 6 files changed, 42 insertions(+), 14 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index cf892c08a88cd..c9c2ca3453502 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1199,10 +1199,10 @@ static inline unsigned int folio_large_order(const struct folio *folio) return folio->_flags_1 & 0xff; } -#ifdef CONFIG_64BIT +#ifdef NR_PAGES_IN_LARGE_FOLIO static inline long folio_large_nr_pages(const struct folio *folio) { - return folio->_folio_nr_pages; + return folio->_nr_pages; } #else static inline long folio_large_nr_pages(const struct folio *folio) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index b1827d78ff891..f3b519fbeca14 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -287,6 +287,11 @@ typedef struct { unsigned long val; } swp_entry_t; +#if defined(CONFIG_MEMCG) || defined(CONFIG_SLAB_OBJ_EXT) +/* We have some extra room after the refcount in tail pages. */ +#define NR_PAGES_IN_LARGE_FOLIO +#endif + /** * struct folio - Represents a contiguous set of bytes. * @flags: Identical to the page flags. @@ -312,7 +317,7 @@ typedef struct { * @_large_mapcount: Do not use directly, call folio_mapcount(). * @_nr_pages_mapped: Do not use outside of rmap and debug code. * @_pincount: Do not use directly, call folio_maybe_dma_pinned(). - * @_folio_nr_pages: Do not use directly, call folio_nr_pages(). + * @_nr_pages: Do not use directly, call folio_nr_pages(). * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h. * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h. * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h. @@ -376,14 +381,23 @@ struct folio { struct { unsigned long _flags_1; unsigned long _head_1; + union { + struct { /* public: */ - atomic_t _large_mapcount; - atomic_t _entire_mapcount; - atomic_t _nr_pages_mapped; - atomic_t _pincount; -#ifdef CONFIG_64BIT - unsigned int _folio_nr_pages; -#endif + atomic_t _large_mapcount; + atomic_t _entire_mapcount; + atomic_t _nr_pages_mapped; + atomic_t _pincount; + /* private: the union with struct page is transitional */ + }; + unsigned long _usable_1[4]; + }; + atomic_t _mapcount_1; + atomic_t _refcount_1; + /* public: */ +#ifdef NR_PAGES_IN_LARGE_FOLIO + unsigned int _nr_pages; +#endif /* NR_PAGES_IN_LARGE_FOLIO */ /* private: the union with struct page is transitional */ }; struct page __page_1; @@ -435,6 +449,8 @@ FOLIO_MATCH(_last_cpupid, _last_cpupid); offsetof(struct page, pg) + sizeof(struct page)) FOLIO_MATCH(flags, _flags_1); FOLIO_MATCH(compound_head, _head_1); +FOLIO_MATCH(_mapcount, _mapcount_1); +FOLIO_MATCH(_refcount, _refcount_1); #undef FOLIO_MATCH #define FOLIO_MATCH(pg, fl) \ static_assert(offsetof(struct folio, fl) == \ diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9a15fd3453ff6..2364990974ba4 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3399,6 +3399,14 @@ static void __split_huge_page(struct page *page, struct list_head *list, int order = folio_order(folio); unsigned int nr = 1 << order; + /* + * Reset any memcg data overlay in the tail pages. folio_nr_pages() + * is unreliable after this point. + */ +#ifdef NR_PAGES_IN_LARGE_FOLIO + folio->_nr_pages = 0; +#endif + /* complete memcg works before add pages to LRU */ split_page_memcg(head, order, new_order); diff --git a/mm/internal.h b/mm/internal.h index 1ac433d2092bb..1cd977413859d 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -725,8 +725,8 @@ static inline void folio_set_order(struct folio *folio, unsigned int order) return; folio->_flags_1 = (folio->_flags_1 & ~0xffUL) | order; -#ifdef CONFIG_64BIT - folio->_folio_nr_pages = 1U << order; +#ifdef NR_PAGES_IN_LARGE_FOLIO + folio->_nr_pages = 1U << order; #endif } diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 57f959af79c56..e1135dff9a863 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1174,8 +1174,12 @@ __always_inline bool free_pages_prepare(struct page *page, if (unlikely(order)) { int i; - if (compound) + if (compound) { page[1].flags &= ~PAGE_FLAGS_SECOND; +#ifdef NR_PAGES_IN_LARGE_FOLIO + folio->_nr_pages = 0; +#endif + } for (i = 1; i < (1 << order); i++) { if (compound) bad += free_tail_page_prepare(page, page + i); diff --git a/mm/page_owner.c b/mm/page_owner.c index 2d6360eaccbb6..a409e2561a8fd 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -507,7 +507,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, rcu_read_lock(); memcg_data = READ_ONCE(page->memcg_data); - if (!memcg_data) + if (!memcg_data || PageTail(page)) goto out_unlock; if (memcg_data & MEMCG_DATA_OBJEXTS)