From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ryusuke Konishi Subject: Re: [RFC] relaxed barrier semantics Date: Tue, 03 Aug 2010 01:47:22 +0900 (JST) Message-ID: <20100803.014722.208373518.ryusuke@osrg.net> References: <20100728090025.GA9252@lst.de> <4C4FF592.9090800@kernel.org> <20100728092859.GA11096@lst.de> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Tejun Heo , Vivek Goyal , Jan Kara , jaxboe@fusionio.com, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp To: Christoph Hellwig Return-path: In-Reply-To: <20100728092859.GA11096@lst.de> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 28 Jul 2010 11:28:59 +0200, Christoph Hellwig wrote: > On Wed, Jul 28, 2010 at 11:17:06AM +0200, Tejun Heo wrote: > > I'll re-read barrier code and see how hard it would be to implement a > > proper solution. > > If we move all filesystems to non-draining barriers with pre- and post- > flushes that might actually be a relatively easy first step. We don't > have the complications to deal with multiple types of barriers to > start with, and it'll fix the issue for devices without volatile write > caches completely. > > I just need some help from the filesystem folks to determine if they > are safe with them. > > I know for sure that ext3 and xfs are from looking through them. And > I know reiserfs is if we make sure it doesn't hit the code path that > relies on it that is currently enabled by the barrier option. > > I'll just need more feedback from ext4, gfs2, btrfs and nilfs folks. With regard to nilfs, barrier is applied to writeback of super block since it saves position of a recent log and this log needs to be written to the platter prior to the super block. And so, I think a pre-flush + a FUA write can be used instead of draining for the barrier use in nilfs. Thanks, Ryusuke Konishi