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Date: Sat, 23 Nov 2013 09:40:38 +1100 From: Dave Chinner <david@...morbit.com> To: Christoph Hellwig <hch@...radead.org> Cc: Martin Boutin <martboutin@...il.com>, "Kernel.org-Linux-RAID" <linux-raid@...r.kernel.org>, Eric Sandeen <sandeen@...hat.com>, "Kernel.org-Linux-EXT4" <linux-ext4@...r.kernel.org>, xfs-oss <xfs@....sgi.com> Subject: Re: Filesystem writes on RAID5 too slow On Fri, Nov 22, 2013 at 01:21:36AM -0800, Christoph Hellwig wrote: > > From: Dave Chinner <dchinner@...hat.com> > > > > The function xfs_bmap_isaeof() is used to indicate that an > > allocation is occurring at or past the end of file, and as such > > should be aligned to the underlying storage geometry if possible. > > > > Commit 27a3f8f ("xfs: introduce xfs_bmap_last_extent") changed the > > behaviour of this function for empty files - it turned off > > allocation alignment for this case accidentally. Hence large initial > > allocations from direct IO are not getting correctly aligned to the > > underlying geometry, and that is cause write performance to drop in > > alignment sensitive configurations. > > > > Fix it by considering allocation into empty files as requiring > > aligned allocation again. > > > > Signed-off-by: Dave Chinner <dchinner@...hat.com> > > Ooops. The fix looks good, > > Reviewed-by: Christoph Hellwig <hch@....de> > > > Might be worth cooking up a test for this, scsi_debug can expose > geometry, and we already have it wired to to large sector size > testing in xfstests. We don't need to screw around with the sector size - that is irrelevant to the problem, and we have an allocation alignment test that is supposed to catch these issues: generic/223. As I said, I have seen occasional failures of that test (once a month, on average) as a result of this bug. It was simply not often enough - running in a hard loop didn't increase the frequency of failures - to be able debug it or to reach my "there's a regression I need to look at" threshold. Perhaps we need to revisit that test and see if we can make it more likely to trigger failures... Cheers, Dave. -- Dave Chinner david@...morbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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