mm, compaction: remove redundant watermark check in compact_finished()
authorVlastimil Babka <vbabka@suse.cz>
Mon, 8 May 2017 22:54:33 +0000 (15:54 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 9 May 2017 00:15:09 +0000 (17:15 -0700)
commit228d7e33903040a0b9dd9a5ee9b3a49c538c0613
tree17eb03bb7f86959fba7506b304e43b3c53ea56c8
parentf25ba6dccc3bfe7e1524f4498a171be038507c45
mm, compaction: remove redundant watermark check in compact_finished()

When detecting whether compaction has succeeded in forming a high-order
page, __compact_finished() employs a watermark check, followed by an own
search for a suitable page in the freelists.  This is not ideal for two
reasons:

 - The watermark check also searches high-order freelists, but has a
   less strict criteria wrt fallback. It's therefore redundant and waste
   of cycles. This was different in the past when high-order watermark
   check attempted to apply reserves to high-order pages.

 - The watermark check might actually fail due to lack of order-0 pages.
   Compaction can't help with that, so there's no point in continuing
   because of that. It's possible that high-order page still exists and
   it terminates.

This patch therefore removes the watermark check.  This should save some
cycles and terminate compaction sooner in some cases.

Link: http://lkml.kernel.org/r/20170307131545.28577-3-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/compaction.c