linux-kernel - Slow Disk I/O

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Date:	Fri, 28 May 2010 11:34:25 -0700
From:	"Brian D. McGrew" <brian@...ionpro.com>
To:	<linux-kernel@...r.kernel.org>
Subject: Slow Disk I/O

Good morning All!

I¹m running CentOS 5.4 x86_64 on a Dell T5500 with 3GB || 12GB or RAM. I¹m
running a 2.6.18-128.el5 kernel.  There is a 500GB SATA drive connected to
the onboard SATA controller.  I can reproduce this problem with CentOS 5.4
i386 on the Dell T5500, T5400 and Optiplex 740¹s.

So now, on to the problem...  In our software, we¹re reading in 5MP image
files in the neighborhood of 500 to 1500 files at a time.  Just a simple
for() loop, open, read, close...  Nothing fancy...

When I have 3GB of RAM in the system, life is good.. Each read takes 8 to
10ms...  This is a good thing!

If I bump the memory up to 12GB, all of the reads are now taking 150 to
200ms.

My default, va.swappines to set to 60...  If I decrease this number, the
problem gets much worse.  If I up va.swappines to 100, the problem gets a
little better, but not a whole lot.

What should I be looking at???

-b

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