[patch 084/101] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

[patch 084/101] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

[akpm]

From: Hugh Dickins <hughd@google.com>
Subject: mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

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%.

Link: http://lkml.kernel.org/r/20160721073614.24395-2-vbabka@suse.cz
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/compaction.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN mm/compaction.c~mm-compaction-dont-isolate-pagewriteback-pages-in-migrate_sync_light-mode mm/compaction.c
--- a/mm/compaction.c~mm-compaction-dont-isolate-pagewriteback-pages-in-migrate_sync_light-mode
+++ a/mm/compaction.c
@@ -1200,7 +1200,7 @@ static isolate_migrate_t isolate_migrate
 	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
_