linux-kernel - Re: [RFC-PATCH 0/7] Memory Compaction v1

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Message-Id: <20100121115636.73BA.A69D9226@jp.fujitsu.com>
Date:	Thu, 21 Jan 2010 12:12:11 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC-PATCH 0/7] Memory Compaction v1

Hi Mel,

Sorry, I haven't read this patch at all.

> The time differences are marginal but bear in mind that this is an ideal
> case of mostly unmapped buffer pages. On nice set of results is between
> allocations 13-18 where no pages were reclaimed, some compaction occured
> and 300 huge pages were allocated in 0.16 seconds. Furthermore, compaction
> allocated a high higher percentage of memory (91% of RAM as huge pages).
> 
> The downside appears to be that the compaction kernel reclaimed even more
> pages than the vanilla kernel. However, take the cut-off point of 880 pages
> that both kernels succeeded. The vanilla kernel had reclaimed 105132 pages
> at that point. The kernel with compaction had reclaimed 59071, less than
> half of what the vanilla kernel reclaimed. i.e. the bulk of pages reclaimed
> with the compaction kernel were to get from 87% of memory allocated to 91%
> as huge pages.
> 
> These results would appear to be an encouraging enough start.
> 
> Comments?

I think "Total pages reclaimed" increasing is not good thing ;)
Honestly, I haven't understand why your patch increase reclaimed and
the exactly meaning of the your tool's rclm field.

Can you share your mesurement script? May I run the same test?

I like this patch, but I don't like increasing reclaim. I'd like to know
this patch require any vmscan change and/or its change mitigate the issue.

Thanks.



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