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Re: Ext4 and xfs problems in dm-thin on allocation and discard

To: Mike Snitzer <msnitzer@xxxxxxxxxx>
Subject: Re: Ext4 and xfs problems in dm-thin on allocation and discard
From: Spelic <spelic@xxxxxxxxxxxxx>
Date: Tue, 19 Jun 2012 15:52:15 +0200
Cc: Lukáš Czerner <lczerner@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Spelic <spelic@xxxxxxxxxxxxx>, device-mapper development <dm-devel@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20120619133041.GB6811@xxxxxxxxxx>
References: <4FDF9EBE.2030809@xxxxxxxxxxxxx> <20120619015745.GJ25389@dastard> <20120619031241.GA3884@xxxxxxxxxx> <alpine.LFD.2.00.1206190816440.2241@xxxxxxxxxxxxxxxxxxxxxxxxx> <20120619131649.GA6811@xxxxxxxxxx> <alpine.LFD.2.00.1206191519320.21961@xxxxxxxxxxxxxxxxxxxxxxxxx> <20120619133041.GB6811@xxxxxxxxxx>
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On 06/19/12 15:30, Mike Snitzer wrote:
I don't recall Spelic saying anything about EOPNOTSUPP. So what has made you zero in on an -EOPNOTSUPP return (which should not be happening)?

Exactly: I do not know if EOPNOTSUPP is being returned or not.

If this helps, I have configured dm-thin via lvm2
  LVM version:     2.02.95(2) (2012-03-06)
  Library version: 1.02.74 (2012-03-06)
  Driver version:  4.22.0

from dmsetup table I only see one option : "skip_block_zeroing", if and only if I configure it with -Zn . I do not see anything regarding ignore_discard

vg1-pooltry1-tpool: 0 20971520 thin-pool 252:1 252:2 2048 0 1 skip_block_zeroing
     vg1-pooltry1_tdata: 0 20971520 linear 9:20 62922752
     vg1-pooltry1_tmeta: 0 8192 linear 9:20 83894272
     vg1-thinlv1: 0 31457280 thin 252:3 1


and in dmesg:
[ 33.685200] device-mapper: thin: Discard unsupported by data device (dm-2): Disabling discard passdown. [ 33.709586] device-mapper: thin: Discard unsupported by data device (dm-6): Disabling discard passdown.


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.


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