From: Yu Zhao <yuzhao@google.com> mainline inclusion from mainline-v6.12-rc7 commit c928807f6f6b6d595a7e199591ae297c81de3aeb category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBC4T0 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- OOM kills due to vastly overestimated free highatomic reserves were observed: ... invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0 ... Node 0 Normal free:1482936kB boost:0kB min:410416kB low:739404kB high:1068392kB reserved_highatomic:1073152KB ... Node 0 Normal: 1292*4kB (ME) 1920*8kB (E) 383*16kB (UE) 220*32kB (ME) 340*64kB (E) 2155*128kB (UE) 3243*256kB (UE) 615*512kB (U) 1*1024kB (M) 0*2048kB 0*4096kB = 1477408kB The second line above shows that the OOM kill was due to the following condition: free (1482936kB) - reserved_highatomic (1073152kB) = 409784KB < min (410416kB) And the third line shows there were no free pages in any MIGRATE_HIGHATOMIC pageblocks, which otherwise would show up as type 'H'. Therefore __zone_watermark_unusable_free() underestimated the usable free memory by over 1GB, which resulted in the unnecessary OOM kill above. The comments in __zone_watermark_unusable_free() warns about the potential risk, i.e., If the caller does not have rights to reserves below the min watermark then subtract the high-atomic reserves. This will over-estimate the size of the atomic reserve but it avoids a search. However, it is possible to keep track of free pages in reserved highatomic pageblocks with a new per-zone counter nr_free_highatomic protected by the zone lock, to avoid a search when calculating the usable free memory. And the cost would be minimal, i.e., simple arithmetics in the highatomic alloc/free/move paths. Note that since nr_free_highatomic can be relatively small, using a per-cpu counter might cause too much drift and defeat its purpose, in addition to the extra memory overhead. Dependson e0932b6c1f94 ("mm: page_alloc: consolidate free page accounting") - see [1] [akpm@linux-foundation.org: s/if/else if/, per Johannes, stealth whitespace tweak] Link: https://lkml.kernel.org/r/20241028182653.3420139-1-yuzhao@google.com Link: https://lkml.kernel.org/r/0d0ddb33-fcdc-43e2-801f-0c1df2031afb@suse.cz [1] Fixes: 0aaa29a56e4f ("mm, page_alloc: reserve pageblocks for high-order atomic allocations on demand") Signed-off-by: Yu Zhao <yuzhao@google.com> Reported-by: Link Lin <linkl@google.com> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Liu Shixin <liushixin2@huawei.com> Conflicts: include/linux/mmzone.h [Context conflicts.] Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com> --- include/linux/mmzone.h | 2 +- mm/page_alloc.c | 10 +++++++--- 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index ebaa85d5ac70..775e8cfc186c 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1032,7 +1032,7 @@ struct zone { CACHELINE_PADDING(_pad3_); - KABI_RESERVE(1) + KABI_USE(1, unsigned long nr_free_highatomic) KABI_RESERVE(2) KABI_RESERVE(3) KABI_RESERVE(4) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index f43076d49e7e..ce4051c7da26 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -639,6 +639,8 @@ compaction_capture(struct capture_control *capc, struct page *page, static inline void account_freepages(struct zone *zone, int nr_pages, int migratetype) { + lockdep_assert_held(&zone->lock); + if (is_migrate_isolate(migratetype)) return; @@ -646,6 +648,9 @@ static inline void account_freepages(struct zone *zone, int nr_pages, if (is_migrate_cma(migratetype)) __mod_zone_page_state(zone, NR_FREE_CMA_PAGES, nr_pages); + else if (is_migrate_highatomic(migratetype)) + WRITE_ONCE(zone->nr_free_highatomic, + zone->nr_free_highatomic + nr_pages); } /* Used for pages not on another list */ @@ -3088,11 +3093,10 @@ static inline long __zone_watermark_unusable_free(struct zone *z, /* * If the caller does not have rights to reserves below the min - * watermark then subtract the high-atomic reserves. This will - * over-estimate the size of the atomic reserve but it avoids a search. + * watermark then subtract the free pages reserved for highatomic. */ if (likely(!(alloc_flags & ALLOC_RESERVES))) - unusable_free += z->nr_reserved_highatomic; + unusable_free += READ_ONCE(z->nr_free_highatomic); #ifdef CONFIG_CMA /* If allocation can't use CMA areas don't use free CMA pages */ -- 2.43.0