The patch titled
Subject: mm, page_alloc: fix potential false positive in __zone_watermark_ok
has been removed from the -mm tree. Its filename was
mm-page_alloc-fix-potential-false-positive-in-__zone_watermark_ok.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm, page_alloc: fix potential false positive in __zone_watermark_ok
Since 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0
allocations"), __zone_watermark_ok() check for high-order allocations will
shortcut per-migratetype free list checks for ALLOC_HARDER allocations,
and return true as long as there's free page of any migratetype. The
intention is that ALLOC_HARDER can allocate from MIGRATE_HIGHATOMIC free
lists, while normal allocations can't.
However, as a side effect, the watermark check will then also return true
when there are pages only on the MIGRATE_ISOLATE list, or (prior to CMA
conversion to ZONE_MOVABLE) on the MIGRATE_CMA list. Since the allocation
cannot actually obtain isolated pages, and might not be able to obtain CMA
pages, this can result in a false positive.
The condition should be rare and perhaps the outcome is not a fatal one.
Still, it's better if the watermark check is correct. There also
shouldn't be a performance tradeoff here.
Link: http://lkml.kernel.org/r/20171102125001.23708-1-vbabka@xxxxxxx
Fixes: 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations")
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-fix-potential-false-positive-in-__zone_watermark_ok mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-fix-potential-false-positive-in-__zone_watermark_ok
+++ a/mm/page_alloc.c
@@ -3041,9 +3041,6 @@ bool __zone_watermark_ok(struct zone *z,
if (!area->nr_free)
continue;
- if (alloc_harder)
- return true;
-
for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) {
if (!list_empty(&area->free_list[mt]))
return true;
@@ -3055,6 +3052,9 @@ bool __zone_watermark_ok(struct zone *z,
return true;
}
#endif
+ if (alloc_harder &&
+ !list_empty(&area->free_list[MIGRATE_HIGHATOMIC]))
+ return true;
}
return false;
}
_
Patches currently in -mm which might be from vbabka@xxxxxxx are
mm-compaction-extend-pageblock_skip_persistent-to-all-compound-pages.patch
mm-compaction-split-off-flag-for-not-updating-skip-hints.patch
mm-compaction-remove-unneeded-pageblock_skip_persistent-checks.patch
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