linux-kernel - RFT: updatedb "morning after" problem [was: Re: -mm merge plans for 2.6.23]

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Message-ID: <20070726094024.GA15583@elte.hu>
Date:	Thu, 26 Jul 2007 11:40:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Frank Kingswood <frank@...gswood-consulting.co.uk>,
	Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ray Lee <ray-lk@...rabbit.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	ck list <ck@....kolivas.org>, Paul Jackson <pj@....com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: RFT: updatedb "morning after" problem [was: Re: -mm merge plans
	for 2.6.23]


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Thu, 26 Jul 2007 11:20:25 +0200 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > Once we give the kernel the knowledge that the dentry wont be used again 
> > by this app, the kernel can do a lot more intelligent decision and not 
> > baloon the dentry cache.
> > 
> > ( we _do_ want to baloon the dentry cache otherwise - for things like 
> >   "find" - having a fast VFS is important. But known-use-once things 
> >   like the daily updatedb job can clearly be annotated properly. )
> 
> Mutter.  /proc/sys/vm/vfs_cache_pressure has been there for what, 
> three years?  Are any distros raising it during the updatedb run yet?

but ... that's system-wide, and the 'dont baloon the dcache' is only a 
property of updatedb. Still, it's useful to debug this thing.

below is an updatedb hack that sets vfs_cache_pressure down to 0 during 
an updatedb run. Could someone who is affected by the 'morning after' 
problem give it a try? If this works then we can think about any other 
measures ...

	Ingo

--- /etc/cron.daily/mlocate.cron.orig
+++ /etc/cron.daily/mlocate.cron
@@ -1,4 +1,7 @@
 #!/bin/sh
 nodevs=$(< /proc/filesystems awk '$1 == "nodev" { print $2 }')
 renice +19 -p $$ >/dev/null 2>&1
+PREV=`cat /proc/sys/vm/vfs_cache_pressure 2>/dev/null`
+echo 0 > /proc/sys/vm/vfs_cache_pressure 2>/dev/null
 /usr/bin/updatedb -f "$nodevs"
+[ "$PREV" != "" ] && echo $PREV > /proc/sys/vm/vfs_cache_pressure 2>/dev/null
-
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