On 10/29/24 01:58, Andrew Morton wrote: > The patch titled > Subject: mm/page_alloc: keep track of free highatomic > has been added to the -mm mm-hotfixes-unstable branch. Its filename is > mm-page_alloc-keep-track-of-free-highatomic.patch In case of mm-hotfixes, the cc stable for 6.12 is unnecessary as it should make it there directly. Perhaps it's the best way, yeah. Thanks, Vlastimil > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-keep-track-of-free-highatomic.patch > > This patch will later appear in the mm-hotfixes-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Yu Zhao <yuzhao@xxxxxxxxxx> > Subject: mm/page_alloc: keep track of free highatomic > Date: Mon, 28 Oct 2024 12:26:53 -0600 > > 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. > > Link: https://lkml.kernel.org/r/20241028182653.3420139-1-yuzhao@xxxxxxxxxx > Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx> > Reported-by: Link Lin <linkl@xxxxxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> [6.12+] > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > include/linux/mmzone.h | 1 + > mm/page_alloc.c | 10 +++++++--- > 2 files changed, 8 insertions(+), 3 deletions(-) > > --- a/include/linux/mmzone.h~mm-page_alloc-keep-track-of-free-highatomic > +++ a/include/linux/mmzone.h > @@ -823,6 +823,7 @@ struct zone { > unsigned long watermark_boost; > > unsigned long nr_reserved_highatomic; > + unsigned long nr_free_highatomic; > > /* > * We don't know if the memory that we're going to allocate will be > --- a/mm/page_alloc.c~mm-page_alloc-keep-track-of-free-highatomic > +++ a/mm/page_alloc.c > @@ -635,6 +635,8 @@ compaction_capture(struct capture_contro > static inline void account_freepages(struct zone *zone, int nr_pages, > int migratetype) > { > + lockdep_assert_held(&zone->lock); > + > if (is_migrate_isolate(migratetype)) > return; > > @@ -642,6 +644,9 @@ static inline void account_freepages(str > > if (is_migrate_cma(migratetype)) > __mod_zone_page_state(zone, NR_FREE_CMA_PAGES, nr_pages); > + > + if (is_migrate_highatomic(migratetype)) > + WRITE_ONCE(zone->nr_free_highatomic, zone->nr_free_highatomic + nr_pages); > } > > /* Used for pages not on another list */ > @@ -3081,11 +3086,10 @@ static inline long __zone_watermark_unus > > /* > * 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 */ > _ > > Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are > > mm-allow-set-clear-page_type-again.patch > mm-multi-gen-lru-remove-mm_leaf_old-and-mm_nonleaf_total-stats.patch > mm-multi-gen-lru-use-pteppmdp_clear_young_notify.patch > mm-page_alloc-keep-track-of-free-highatomic.patch >
