linux-kernel - Re: Understanding I/O behaviour

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Message-ID: <46D59DE2.2070405@redhat.com>
Date:	Wed, 29 Aug 2007 12:25:06 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	spamtrap@...bisoft.de
CC:	linux-kernel@...r.kernel.org,
	Peter zijlstra <a.p.zijlstra@...llo.nl>, mingo@...hat.com
Subject: Re: Understanding I/O behaviour - next try

On 08/28/2007 11:53 AM, Martin Knoblauch wrote:
> 
>  The basic setup is a dual x86_64 box with 8 GB of memory. The DL380
> has a HW RAID5, made from 4x72GB disks and about 100 MB write cache.
> The performance of the block device with O_DIRECT is about 90 MB/sec.
> 
>  The problematic behaviour comes when we are moving large files through
> the system. The file usage in this case is mostly "use once" or
> streaming. As soon as the amount of file data is larger than 7.5 GB, we
> see occasional unresponsiveness of the system (e.g. no more ssh
> connections into the box) of more than 1 or 2 minutes (!) duration
> (kernels up to 2.6.19). Load goes up, mainly due to pdflush threads and
> some other poor guys being in "D" state.

Try booting with "mem=4096M", "mem=2048M", ...
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