Commit 4996fc54 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

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: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirks^H^Hski <luto@kernel.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Michal Koutn <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: tejun heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 1ea5212a

include/linux/mm.h

+2 −2
Original line number Diff line number Diff line
@@ -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)

include/linux/mm_types.h

+24 −8
Original line number Diff line number Diff line
@@ -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

	/* 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) ==			\

mm/huge_memory.c

+8 −0
Original line number Diff line number Diff line
@@ -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);

mm/internal.h

+2 −2
Original line number Diff line number Diff line
@@ -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

}

mm/page_alloc.c

+5 −1
Original line number Diff line number Diff line
@@ -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);