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Date: Tue, 19 Jun 2012 14:48:59 -0400 From: Mike Snitzer <snitzer@...hat.com> To: Spelic <spelic@...ftmail.org> Cc: Lukáš Czerner <lczerner@...hat.com>, device-mapper development <dm-devel@...hat.com>, linux-ext4@...r.kernel.org, Dave Chinner <david@...morbit.com>, xfs@....sgi.com Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard On Tue, Jun 19 2012 at 10:44am -0400, Mike Snitzer <snitzer@...hat.com> wrote: > On Tue, Jun 19 2012 at 9:52am -0400, > Spelic <spelic@...ftmail.org> wrote: > > > I do not know what is the mechanism for which xfs cannot unmap > > blocks from dm-thin, but it really can't. > > If anyone has dm-thin installed he can try. This is 100% > > reproducible for me. > > I was initially surprised by this considering the thinp-test-suite does > test a compilebench workload against xfs and ext4 using online discard > (-o discard). > > But I just modified that test to use a thin-pool with 'ignore_discard' > and the test still passed on both ext4 and xfs. > > So there is more work needed in the thinp-test-suite to use blktrace > hooks to verify that discards are occuring when the compilebench > generated files are removed. > > I'll work through that and report back. blktrace shows discards for both xfs and ext4. But in general xfs is issuing discards with much smaller extents than ext4 does, e.g.: to the thin device: + 128 vs + 32 to the thin-pool's data device: + 120 vs + 16 -- 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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