Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 16/66] mm, page_alloc: fix potential false positive in __zone_watermark_ok | Date | Mon, 29 Jan 2018 13:56:40 +0100 |
| |
4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vlastimil Babka <vbabka@suse.cz>
commit b050e3769c6b4013bb937e879fc43bf1847ee819 upstream.
Since commit 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@suse.cz Fixes: 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations") Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Mel Gorman <mgorman@techsingularity.net> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Rik van Riel <riel@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/page_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2821,9 +2821,6 @@ 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; @@ -2835,6 +2832,9 @@ bool __zone_watermark_ok(struct zone *z, return true; } #endif + if (alloc_harder && + !list_empty(&area->free_list[MIGRATE_HIGHATOMIC])) + return true; } return false; }
| |