linux-kernel - Re: userspace pagecache management tool

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Message-Id: <20070303173933.9f46459c.akpm@linux-foundation.org>
Date:	Sat, 3 Mar 2007 17:39:33 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Lee Revell" <rlrevell@...-job.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: userspace pagecache management tool

On Sat, 3 Mar 2007 20:16:09 -0500 "Lee Revell" <rlrevell@...-job.com> wrote:

> On 3/3/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > The tool uses an LD_PRELOAD hack to intercept glibc's read(), pread(),
> > write(), pwrite(), close() and dup2() functions.  pagecache control is done
> > via posix_fadvise() and sync_file_range().
> >
> 
> How could this have any effect on the updatedb problem?  updatedb does
> not read() anything, it just open()s and stat()s every file on the
> disk.
> 

err, good point.  _one_ of those dang things which goes off when you've
stayed up too late does a lot of pagecache IO, not sure which one.  Maybe
rpmq?  But I'd expect that to be doing direct-io.

But yes, updatedb's pagecache usage will be mainly metadata, and this tool
doesn't address metadata pagecache, although it could do so.

<does an updatedb on a modest system>

It instantiated 5MB of pagecache and 20MB of slab, took about one minute.

<runs all the other things in /etc/cron.daily>

rpm uses rather a lot of pagecache.

So yes, it looks like updatedb is a slab problem.
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