linux-kernel - Re: [PATCH 2/2] mm: Abort reclaim/compaction if compaction can proceed

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Date:	Fri, 7 Oct 2011 21:24:17 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	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 2/2] mm: Abort reclaim/compaction if compaction can
 proceed

On Fri, Oct 07, 2011 at 04:07:06PM -0400, Rik van Riel wrote:
> On 10/07/2011 11:17 AM, Mel Gorman wrote:
> >If compaction can proceed, shrink_zones() stops doing any work but
> >the callers still shrink_slab(), raises the priority and potentially
> >sleeps.  This patch aborts direct reclaim/compaction entirely if
> >compaction can proceed.
> >
> >Signed-off-by: Mel Gorman<mgorman@...e.de>
> 
> This patch makes sense to me, but I have not tested it like
> the first one.
> 

Do if you can.

> Mel, have you tested this patch?

Yes.

> Did you see any changed
> behaviour vs. just the first patch?
> 

It's marginal and could be confirmation bias on my part. Basically,
there is noise when this path is being exercised but there were fewer
slabs scanned.  However, I don't know what the variances are and
whether the reduction was within the noise or not but it makes sense
that it would scan less.  If I profiled carefully, I might be able
to show that a few additional cycles are spent raising the priority
but it would be marginal.

While patch 1 is very clear, patch 2 depends on reviewers deciding it
"makes sense".

> Having said that, I'm pretty sure the patch is ok :)
> 

Care to ack?

-- 
Mel Gorman
SUSE Labs
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