linux-kernel - Re: [patch] mm, thp: do not perform sync compaction on pagefault

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Date:	Thu, 1 May 2014 15:39:12 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Greg Thelen <gthelen@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [patch] mm, thp: do not perform sync compaction on pagefault

2014-05-01 9:45 GMT+09:00 David Rientjes <rientjes@...gle.com>:
> Synchronous memory compaction can be very expensive: it can iterate an enormous
> amount of memory without aborting and it can wait on page locks and writeback to
> complete if a pageblock cannot be defragmented.
> Unfortunately, it's too expensive for pagefault for transparent hugepages and
> it's much better to simply fallback to pages.  On 128GB machines, we find that
> synchronous memory compaction can take O(seconds) for a single thp fault.

Hello,

AFAIK, synchronous compaction doesn't wait the page on writeback.
sync compaction pass MIGRATE_SYNC_LIGHT for migrate_mode,
instead of MIGRATE_SYNC. It results in skipping the page on writeback.

Thanks.
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