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Date: Sun, 4 Jan 2009 18:58:27 -0500
From: Theodore Tso <tytso@mit.edu>
To: Pavel Machek <pavel@suse.cz>
Cc: "Alexander E. Patrakov" <patrakov@gmail.com>,
       kernel list <linux-kernel@vger.kernel.org>,
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       rdunlap@xenotime.net, linux-doc@vger.kernel.org,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: document ext3 requirements
Message-ID: <20090104235827.GH22958@mit.edu>
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References: <20090103123813.GA1512@ucw.cz> <4960BB2D.3060000@gmail.com> <20090104183834.GB17558@mit.edu> <20090104223756.GD1913@elf.ucw.cz>
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On Sun, Jan 04, 2009 at 11:37:56PM +0100, Pavel Machek wrote:
> 
> Are you sure you need to have thrashing? AFAICT metadata + fsync heavy
> workload should be enough... and there were scripts to easily repeat
> that.

The memory pressure is needed to force disk buffers out to disk sooner
than fsync() would normally force buffers out.  The scripts which I've
seen induced memory pressure.  If the disk is *super* aggressive at
reordering writes, I suppose a heavy fsync workload might be enough on
its own, but in practice, it's generally not enough.

							- Ted