linux-kernel - Re: [PATCH 1/2] mm: vmscan: Limit direct reclaim for higher order allocations

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Date:	Sun, 9 Oct 2011 17:02:55 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	akpm@...ux-foundation.org, Josh Boyer <jwboyer@...hat.com>,
	aarcange@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: vmscan: Limit direct reclaim for higher order
 allocations

On Fri, Oct 07, 2011 at 04:17:22PM +0100, Mel Gorman wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> When suffering from memory fragmentation due to unfreeable pages,
> THP page faults will repeatedly try to compact memory.  Due to the
> unfreeable pages, compaction fails.
> 
> Needless to say, at that point page reclaim also fails to create
> free contiguous 2MB areas.  However, that doesn't stop the current
> code from trying, over and over again, and freeing a minimum of 4MB
> (2UL << sc->order pages) at every single invocation.
> 
> This resulted in my 12GB system having 2-3GB free memory, a
> corresponding amount of used swap and very sluggish response times.
> 
> This can be avoided by having the direct reclaim code not reclaim from
> zones that already have plenty of free memory available for compaction.
> 
> If compaction still fails due to unmovable memory, doing additional
> reclaim will only hurt the system, not help.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

-- 
Kinds regards,
Minchan Kim
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