[RFC 2/8] compaction: make isolate_lru_page with filter aware

[Minchan Kim <minchan.kim@gmail.com>]

In async mode, compaction doesn't migrate dirty or writeback pages.
So, it's meaningless to pick the page and re-add it to lru list.

Of course, when we isolate the page in compaction, the page might
be dirty or writeback but when we try to migrate the page, the page
would be not dirty, writeback. So it could be migrated. But it's
very unlikely as isolate and migration cycle is much faster than
writeout.

So, this patch helps cpu and prevent unnecessary LRU churning.

Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
---
 mm/compaction.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index dea32e3..9f80b5a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -335,7 +335,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
 		}
 
 		/* Try isolate the page */
-		if (__isolate_lru_page(page, ISOLATE_BOTH, 0, 0, 0) != 0)
+		if (__isolate_lru_page(page, ISOLATE_BOTH, 0, !cc->sync, 0) != 0)
 			continue;
 
 		VM_BUG_ON(PageTransCompound(page));
-- 
1.7.1

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