linux-kernel - Re: [patch v3 5/6] mm, thp: avoid excessive compaction latency during fault

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Message-ID: <20140507093935.GE23991@suse.de>
Date:	Wed, 7 May 2014 10:39:35 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch v3 5/6] mm, thp: avoid excessive compaction latency
 during fault

On Tue, May 06, 2014 at 07:22:50PM -0700, David Rientjes wrote:
> Synchronous memory compaction can be very expensive: it can iterate an enormous 
> amount of memory without aborting, constantly rescheduling, waiting on page
> locks and lru_lock, etc, if a pageblock cannot be defragmented.
> 
> Unfortunately, it's too expensive for transparent hugepage page faults 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.
> 
> Now that async compaction remembers where it left off without strictly relying
> on sync compaction, this makes thp allocations best-effort without causing
> egregious latency during fault.  We still need to retry async compaction after
> reclaim, but this won't stall for seconds.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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