linux-ext4 - Re: buffered writeback torture program

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Message-ID: <20110421180213.GA19255@infradead.org>
Date:	Thu, 21 Apr 2011 14:02:13 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 Thu, Apr 21, 2011 at 11:59:37AM -0600, Andreas Dilger wrote:
> 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.

It doesn't cluster any writes in an extent.  It only writes out
additional dirty pages directly following that one we were asked to
write out.  As soon as we hit a non-dirty page we give up.

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