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Re: [PATCH 3/4] XFS: Return case-insensitive match for dentry cache

To: "Christoph Hellwig" <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/4] XFS: Return case-insensitive match for dentry cache
From: "Barry Naujok" <bnaujok@xxxxxxx>
Date: Thu, 15 May 2008 15:14:54 +1000
Cc: xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, aia21@xxxxxxxxxx
In-reply-to: <20080515045700.GA4328@infradead.org>
Organization: SGI
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On Thu, 15 May 2008 14:57:00 +1000, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

On Wed, May 14, 2008 at 05:55:45PM +1000, Barry Naujok wrote:
Not quite sure if this is the right test, but I did 1000 creates on
a brand new filesystem with and without ci on my SATA drive, both
sustained almost 600 creates per second.

I believe creates would be the worst case scenario for not adding
negative dentries?

No, negative dentries shouldn't have any effect on that. negative entries help to optimize away lookups. E.g. thing of the PATH variable and say your shell is not in the first directory listed there. Having a negative dentry for it means that you don't have to do a lookup in the first directories everytime someone wants to use the shell.

Ah, that makes more sense. I did a test of a million lookups to a non-existant file in a short-form directory (dual 1.6G opteron):

CI = 4.6s
non-CI = 3.7s

And a directory with 10000 files:

CI = 10.3s
non-CI = 3.9s


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