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

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Date:	Mon, 3 Dec 2007 15:11:41 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Stephen Lord <lord@....org>
Cc:	Timothy Shimmin <tes@....com>,
	Christoph Hellwig <hch@...radead.org>,
	Chris Wedgwood <cw@...f.org>, linux-xfs@....sgi.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfs: revert to double-buffering readdir

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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