| Message ID | 20240829165627.2256514-5-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: MM owner tracking for large folios (!hugetlb) + CONFIG_NO_PAGE_MAPCOUNT | expand |
On Thu, Aug 29, 2024 at 06:56:07PM +0200, David Hildenbrand wrote: > 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". > > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> BTW, have anybody evaluated how much (if anything) do we gain we a separate _nr_pages field in struct folio comparing to calculating it based on the order in _flags_1? Mask+shift should be pretty cheap.
On 23.10.24 13:38, Kirill A. Shutemov wrote: > On Thu, Aug 29, 2024 at 06:56:07PM +0200, David Hildenbrand wrote: >> 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". >> >> Signed-off-by: David Hildenbrand <david@redhat.com> > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > BTW, have anybody evaluated how much (if anything) do we gain we a > separate _nr_pages field in struct folio comparing to calculating it > based on the order in _flags_1? Mask+shift should be pretty cheap. I recall that Willy did, and it's mostly getting rid of a single instruction in loads of places. $ git grep folio_nr_pages | wc -l 254 [my first intuition was also to just remove it, but this way seems easy to just maintain it for now]
diff --git a/include/linux/mm.h b/include/linux/mm.h index fa8b6ce54235c..98411e53da916 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1078,8 +1078,8 @@ static inline unsigned int folio_large_order(const struct folio *folio) static inline long folio_large_nr_pages(const struct folio *folio) { -#ifdef CONFIG_64BIT - return folio->_folio_nr_pages; +#ifdef NR_PAGES_IN_LARGE_FOLIO + return folio->_nr_pages; #else return 1L << folio_large_order(folio); #endif diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6e3bdf8e38bca..480548552ea54 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -283,6 +283,11 @@ 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. @@ -305,7 +310,7 @@ 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. @@ -366,13 +371,20 @@ struct folio { unsigned long _flags_1; unsigned long _head_1; /* 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 + union { + struct { + atomic_t _large_mapcount; + atomic_t _entire_mapcount; + atomic_t _nr_pages_mapped; + atomic_t _pincount; + }; + unsigned long _usable_1[4]; + }; + atomic_t _mapcount_1; + atomic_t _refcount_1; +#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; @@ -424,6 +436,8 @@ 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 15418ffdd3774..28d12573fcf8c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3171,6 +3171,14 @@ 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 97d6b94429ebd..f627fd2200464 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -625,8 +625,8 @@ 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 c2ffccf9d2131..e276cbaf97054 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1077,8 +1077,12 @@ __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 + ((struct folio *)page)->_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)
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". Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm.h | 4 ++-- include/linux/mm_types.h | 30 ++++++++++++++++++++++-------- mm/huge_memory.c | 8 ++++++++ mm/internal.h | 4 ++-- mm/page_alloc.c | 6 +++++- mm/page_owner.c | 2 +- 6 files changed, 40 insertions(+), 14 deletions(-)