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Re: [PATCH] xfs: revert to double-buffering readdir

To: Stephen Lord <lord@xxxxxxx>
Subject: Re: [PATCH] xfs: revert to double-buffering readdir
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 3 Dec 2007 15:11:41 +0000
Cc: Timothy Shimmin <tes@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Chris Wedgwood <cw@xxxxxxxx>, linux-xfs@xxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>
In-reply-to: <165B249C-FE97-4B27-927B-B39DE316CB23@xfs.org>
References: <20071114070400.GA25708@puku.stupidest.org> <20071125163014.GA17922@infradead.org> <474FBA21.4070201@sgi.com> <165B249C-FE97-4B27-927B-B39DE316CB23@xfs.org>
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Mutt/1.5.17 (2007-11-01)
On Fri, Nov 30, 2007 at 04:36:25PM -0600, Stephen Lord wrote:
> Wow, was it really that long ago!
> Looks like the readdir is in the bowels of the btree code when filldir gets 
> called
> here, there are probably locks on several buffers in the btree at this 
> point. This
> will only show up for large directories I bet.

Chris saw it with block-form directories.  I've verified it works fine
with short-form directories, and the leaf code looks like it could
happen aswell.  I also remember gfs2 running into a similar problem.

> The xfs readdir code has the complete xfs inode number in its hands at this 
> point
> (filldir is not necessarily getting all the bits of it). All we are doing 
> the lookup
> for really is to get the inode number back again so we can get the inode
> and get the attributes. Rather dumb really. There has got to be a way of
> doing a callout structure here so that the inode number can be pushed
> through filldir and back into an fs specific call. The fs then can do a 
> lookup
> by id - which is what it does most of the time for resolving nfs handles
> anyway. Should be more efficient than the current scheme.

Yes, a lot more efficient.  But it means adding a new operation for use
by the nfs server.

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