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

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Date:	Fri, 07 Oct 2011 18:42:42 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
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 10/07/2011 04:24 PM, Mel Gorman wrote:
> 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.

I'll probably build a kernel with your patch in it on
Sunday - I'll be walking across a mountain tomorrow :)

> 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.

This seems clear enough.

> 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?

Sure.

Acked-by: Rik van Riel <riel@...hat.com>


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