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BACKPORT: mm/page_alloc: keep track of free highatomic

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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: 0aaa29a56e ("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>

Bug: 406708503
(cherry picked from commit c928807f6f6b6d595a7e199591ae297c81de3aeb)
[ To avoid breaking the ABI, remove the newly added variable nr_free_highatomic
from the zone and replace it with an array free_highatomics[MAX_NR_ZONES] ]

Change-Id: I099bdc4a9a60d6d816cb17a84f1a71b6084e9f78
Signed-off-by: yipeng xiang <yipengxiang@honor.corp-partner.google.com>
This commit is contained in:
Yu Zhao
2024-10-28 12:26:53 -06:00
committed by Suren Baghdasaryan
parent b9e2be445a
commit 9743210ec0
1 changed files with 9 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
mm/page_alloc.c
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@@ -323,6 +323,8 @@ const char * const migratetype_names[MIGRATE_TYPES] = {
#endif
};
unsigned long free_highatomics[MAX_NR_ZONES] = {0};
int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
static int watermark_boost_factor __read_mostly = 15000;
@@ -759,6 +761,8 @@ 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;
@@ -766,6 +770,9 @@ 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(free_highatomics[zone_idx(zone)],
free_highatomics[zone_idx(zone)] + nr_pages);
}
/* Used for pages not on another list */
@@ -3204,11 +3211,10 @@ 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(free_highatomics[zone_idx(z)]);
#ifdef CONFIG_CMA
/* If allocation can't use CMA areas don't use free CMA pages */