From: Vlastimil Babka <vbabka@suse.cz> To: Andrew Morton <akpm@linux-foundation.org> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman <mgorman@techsingularity.net>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Rik van Riel <riel@redhat.com>, David Rientjes <rientjes@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Vlastimil Babka <vbabka@suse.cz> Subject: [PATCH] mm, page_alloc: fix potential false positive in __zone_watermark_ok Date: Thu, 2 Nov 2017 13:50:01 +0100 Message-ID: <20171102125001.23708-1-vbabka@suse.cz> (raw) 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. Fixes: 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations") Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- mm/page_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 79cdac1fee42..f43039945148 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3032,9 +3032,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, 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; @@ -3044,6 +3041,9 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, if (!list_empty(&area->free_list[MIGRATE_CMA])) return true; #endif + if (alloc_harder && + !list_empty(&area->free_list[MIGRATE_HIGHATOMIC])) + return true; } return false; } -- 2.14.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next reply index Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-02 12:50 Vlastimil Babka [this message] 2017-11-02 13:23 ` Mel Gorman
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