linux-ext4 - Re: buffered writeback torture program

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Message-Id: <93CB867E-B908-4B38-A146-A9DC958ACF64@dilger.ca>
Date:	Thu, 21 Apr 2011 11:59:37 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Chris Mason <chris.mason@...cle.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>, xfs <xfs@....sgi.com>,
	jack <jack@...e.cz>, axboe <axboe@...nel.dk>,
	dchinner <dchinner@...hat.com>
Subject: Re: buffered writeback torture program

On 2011-04-21, at 11:41 AM, Christoph Hellwig wrote:
> On Thu, Apr 21, 2011 at 01:34:44PM -0400, Chris Mason wrote:
>> Sorry, this doesn't do it.  I think that given what a strange special
>> case this is, we're best off waiting for the IO-less throttling, and
>> maybe changing the code in xfs/ext4 to be a little more seek aware.  Or
>> maybe not, it has to get written eventually either way.
> 
> I'm not sure what you mean with seek aware.  XFS only clusters
> additional pages that are in the same extent, and in fact only does
> so for asynchrononous writeback.  Not sure how this should be more
> seek aware.

But doesn't XFS have potentially very large extents, especially in the case of files that were fallocate()'d or linearly written?  If there is a single 8GB extent, and then random writes within that extent (seems very database like) grouping the all of the writes in the extent doesn't seem so great.


Cheers, Andreas





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