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

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Message-ID: <20100121101112.GH5154@csn.ul.ie>
Date:	Thu, 21 Jan 2010 10:11:12 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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

On Thu, Jan 21, 2010 at 12:12:11PM +0900, KOSAKI Motohiro wrote:
> 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 ;)

First, I made a mistake in the patch. With the bug fixed, they're
reduced. See the post later in the thread
http://lkml.org/lkml/2010/1/6/215

> 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?
> 

Unfortunately at the moment it's part of a mini-testgrid setup I run out
of the house. It doesn't lend itself to being stand-alone. I'll break it
out as part of the next release.

> 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.
> 

With the bug repaired, reclaims go from 105132 to 45935 with more huge
pages allocated so right now, no special action is required.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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