linux-kernel - Re: [ck] Re: -mm merge plans for 2.6.23

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Date:	Mon, 06 Aug 2007 12:11:53 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Matthew Hawkins <darthmdh@...il.com>
CC:	Ray Lee <ray-lk@...rabbit.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	linux-kernel@...r.kernel.org, ck list <ck@....kolivas.org>,
	linux-mm@...ck.org, Paul Jackson <pj@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [ck] Re: -mm merge plans for 2.6.23

Matthew Hawkins wrote:
> On 7/25/07, Nick Piggin <nickpiggin@...oo.com.au> wrote:
> 
>>I guess /proc/meminfo, /proc/zoneinfo, /proc/vmstat, /proc/slabinfo
>>before and after the updatedb run with the latest kernel would be a
>>first step. top and vmstat output during the run wouldn't hurt either.
> 
> 
> Hi Nick,
> 
> I've attached two files with this kind of info.  Being up at the cron
> hours of the morning meant I got a better picture of what my system is
> doing.  Here's a short summary of what I saw in top:
> 
> beagleindexer used gobs of ram.  600M or so (I have 1G)

Hmm OK, beagleindexer. I thought beagle didn't need frequent reindexing
because of inotify? Oh well...

> updatedb didn't use much ram, but while it was running kswapd kept on
> frequenting the top 10 cpu hogs - it would stick around for 5 seconds
> or so then disappear for no more than 10 seconds, then come back
> again.  This behaviour persisted during the run.  updatedb ran third
> (beagleindexer was first, then update-dlocatedb)

Kswapd will use CPU when memory is low, even if there is no swapping.

Your "buffers" grew by 600% (from 50MB to 350MB), and slab also grew
by a few thousand entries. This is not just a problem when it pushes
out swap, it will also harm filebacked working set.

This (which Ray's traces also show) is a bit of a problem. As Andrew
noticed, use-once isn't working well for buffer cache, and it doesn't
really for dentry and inode cache either (although those don't seem
to be as much of a problem on your workload).

Andrew has done a little test patch for this in -mm, but it probably
wants more work and testing. If you can test the -mm kernel and see
if things are improved, that would help.

-- 
SUSE Labs, Novell Inc.
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