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Re: XFS unlink still slow on 3.1.9 kernel ?

To: Richard Ems <richard.ems@xxxxxxxxxxxxxxxxx>
Subject: Re: XFS unlink still slow on 3.1.9 kernel ?
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 14 Feb 2012 14:45:35 -0500
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <4F3A5440.409@xxxxxxxxxxxxxxxxx>
References: <4F394116.8080200@xxxxxxxxxxxxxxxxx> <20120214000924.GF14132@dastard> <4F3A5440.409@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Feb 14, 2012 at 01:32:00PM +0100, Richard Ems wrote:
> > You won't if the directory traversal is seek bound and that is the
> > limiting factor for performance.
> *Seek bound*? *When* is the directory traversal *seek bound*?

You read the inode for the directory first, then the external attribute
block for the ACLs, then if the directory isn't tiny you'll start reading
directory blocks, the more the larger the directory is, and if the
filesystem is close to beeing full they often will be non-contiguous.
Then you read the inode for each file/directory in it, then the external
attribute block, then the extent list, and so on.

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