The patch titled
Subject: mm/page_alloc.c: fix watermark check in __zone_watermark_ok()
has been added to the -mm tree. Its filename is
mm-page_alloc-fix-watermark-check-in-__zone_watermark_ok.patch
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From: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>
Subject: mm/page_alloc.c: fix watermark check in __zone_watermark_ok()
The watermark check consists of two sub-checks. The first one is:
if (free_pages <= min + lowmem_reserve)
return false;
The check assures that there is minimal amount of RAM in the zone. If CMA
is used then the free_pages is reduced by the number of free pages in CMA
prior to the over-mentioned check.
if (!(alloc_flags & ALLOC_CMA))
free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
This prevents the zone from being drained from pages available for
non-movable allocations.
The second check prevents the zone from getting too fragmented.
for (o = 0; o < order; o++) {
free_pages -= z->free_area[o].nr_free << o;
min >>= 1;
if (free_pages <= min)
return false;
}
The field z->free_area[o].nr_free is equal to the number of free pages
including free CMA pages. Therefore the CMA pages are subtracted twice.
This may cause a false positive fail of __zone_watermark_ok() if the CMA
area gets strongly fragmented. In such a case there are many 0-order free
pages located in CMA. Those pages are subtracted twice therefore they
will quickly drain free_pages during the check against fragmentation. The
test fails even though there are many free non-cma pages in the zone.
This patch fixes this issue by subtracting CMA pages only for a purpose of
(free_pages <= min + lowmem_reserve) check.
Signed-off-by: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-fix-watermark-check-in-__zone_watermark_ok mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-fix-watermark-check-in-__zone_watermark_ok
+++ a/mm/page_alloc.c
@@ -1628,6 +1628,7 @@ static bool __zone_watermark_ok(struct z
long min = mark;
long lowmem_reserve = z->lowmem_reserve[classzone_idx];
int o;
+ long free_cma = 0;
free_pages -= (1 << order) - 1;
if (alloc_flags & ALLOC_HIGH)
@@ -1637,9 +1638,10 @@ static bool __zone_watermark_ok(struct z
#ifdef CONFIG_CMA
/* If allocation can't use CMA areas don't use free CMA pages */
if (!(alloc_flags & ALLOC_CMA))
- free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
+ free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
#endif
- if (free_pages <= min + lowmem_reserve)
+
+ if (free_pages - free_cma <= min + lowmem_reserve)
return false;
for (o = 0; o < order; o++) {
/* At the next order, this order's pages become unavailable */
_
Patches currently in -mm which might be from t.stanislaws@xxxxxxxxxxx are
origin.patch
mm-page_alloc-fix-watermark-check-in-__zone_watermark_ok.patch
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