Subject: Re: 2.6 vm/elevator loading down disks where 2.4 does not
From: Clint Byrum <cbyrum@spamaps.org>
To: Andrew Morton <akpm@osdl.org>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <20040609162548.63d69b78.akpm@osdl.org>
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	 <20040609162548.63d69b78.akpm@osdl.org>
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Date: Fri, 11 Jun 2004 09:45:36 -0700
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On Wed, 2004-06-09 at 16:25, Andrew Morton wrote:
> Possibly a memory zone problem.  Could you try booting with "mem=896m" on
> the kernel command line, see how that affects things?

This took a while longer to try, as I didn't want to unfairly test it
against a box with 1G of RAM. So I rebooted my 2.4.23 and 2.6.7-rc3 test
boxes with mem=896m. No change in the 5:1 ratio when comparing 2.6's
disk reads to 2.4's. Of course, both boxes ended up reading from the
disk more often, as they had less RAM for cache. I was unable to run a
long test as I did before, but I'm confident the 3 hours I did run tests
for show that this isn't a memory zone problem.

I still think this behavior is happening because useful pages are being
removed from the page cache too soon. Maybe this is happening because of
excessive readahead?

-cb

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