From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755946Ab2LNBsM (ORCPT ); Thu, 13 Dec 2012 20:48:12 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:64952 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755862Ab2LNBsJ (ORCPT ); Thu, 13 Dec 2012 20:48:09 -0500 Message-ID: <50CA8556.7030905@mit.edu> Date: Thu, 13 Dec 2012 17:48:06 -0800 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: "Darrick J. Wong" CC: axboe@kernel.dk, lucho@ionkov.net, jack@suse.cz, ericvh@gmail.com, viro@zeniv.linux.org.uk, rminnich@sandia.gov, tytso@mit.edu, martin.petersen@oracle.com, neilb@suse.de, david@fromorbit.com, Zheng Liu , linux-kernel@vger.kernel.org, hch@infradead.org, linux-fsdevel@vger.kernel.org, adilger.kernel@dilger.ca, bharrosh@panasas.com, jlayton@samba.org, v9fs-developer@lists.sourceforge.net, linux-ext4@vger.kernel.org Subject: Re: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write References: <20121213080740.23360.16346.stgit@blackbox.djwong.org> <20121213080811.23360.98131.stgit@blackbox.djwong.org> In-Reply-To: <20121213080811.23360.98131.stgit@blackbox.djwong.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/13/2012 12:08 AM, Darrick J. Wong wrote: > Several complaints have been received regarding long file write latencies when > memory pages must be held stable during writeback. Since it might not be > acceptable to stall programs for the entire duration of a page write (which may > take many milliseconds even on good hardware), enable a second strategy wherein > pages are snapshotted as part of submit_bio; the snapshot can be held stable > while writes continue. > > This provides a band-aid to provide stable page writes on jbd without needing > to backport the fixed locking scheme in jbd2. A mount option is added to ext4 > to allow administrators to enable it there. I'm a bit confused as to what it has to do with ext3. Wouldn't this be useful as a mount option everywhere, though? If this becomes widely used, would it be better to snapshot on wait_for_stable_page instead of on io submission? FWIW, I'm about to pound pretty hard on this whole patchset on a box that doesn't need stable pages. I'll let you know how it goes. --Andy