linux-kernel - [PATCH 1/8] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC

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Message-Id: <20160718112302.27381-2-vbabka@suse.cz>
Date:	Mon, 18 Jul 2016 13:22:55 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Michal Hocko <mhocko@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 1/8] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

From: Hugh Dickins <hughd@...gle.com>

At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to
isolate a PageWriteback page, which __unmap_and_move() then rejects
with -EBUSY: of course the writeback might complete in between, but
that's not what we usually expect, so probably better not to isolate it.

When tested by stress-highalloc from mmtests, this has reduced the number of
page migrate failures by 60-70%.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
Acked-by: Michal Hocko <mhocko@...e.com>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index cd93ea24c565..892e397655dc 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1200,7 +1200,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 	struct page *page;
 	const isolate_mode_t isolate_mode =
 		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
-		(cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
+		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
 
 	/*
 	 * Start at where we last stopped, or beginning of the zone as
-- 
2.9.0