From: Mike Snitzer Subject: Re: [Bug 14354] Status of barrier requests in LVM and dm-crypt? Date: Tue, 13 Oct 2009 10:49:45 -0400 Message-ID: <20091013144945.GA22223@redhat.com> References: Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mikulas Patocka , dm-devel@redhat.com, linux-ext4@vger.kernel.org, bugzilla-daemon@bugzilla.kernel.org To: "Theodore Ts'o" Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com List-Id: linux-ext4.vger.kernel.org On Mon, Oct 12 2009 at 2:15pm -0400, Theodore Ts'o wrote: > Hi, I'm trying to track down a problem relating to ext4 problems, in > kernel bugzilla 14354. Originally it was thought this was a regression > 2.6.31->2.6.32-rc1 regression, but the Aneesh Kumar's report shows a > very similar fsck transcript using a 2.6.30-1 kernel (which makes makes > it unclear whether this is really a regression or not), and all three > reports are tied together by the use of device-mapper. > > The fsck logs are consistent barriers being disabled. As I recall under > some circumstances device mapper silently drops barrier requests --- I > thought this was fixed for device mapper in some cases. What's the > current status of barrier requests in device mapper? Are they > faithfully passed for standard (non-RAID) LVM2 volumes? When was this > changed? What about dm-crypto volumes? (One of the reports was with a > dm-crypt volume from what I can tell.) Barrier infrastructure started to get added to the DM core in 2.6.30, see: http://git.kernel.org/linus/af7e466a1ace But barriers were not enabled for all DM targets (_except_ dm-multipath) until 2.6.31. So 2.6.31's dm-crypt does support barriers, see: http://git.kernel.org/linus/647c7db14ef9 If the underlying device(s) support barriers DM should faithfully pass them on (again except for dm-multipath). Also, requests with barriers that result in -EOPNOTSUPP are retried without the barrier, see: http://git.kernel.org/linus/51aa32284958 Mike