From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753387Ab3ISJke (ORCPT ); Thu, 19 Sep 2013 05:40:34 -0400 Received: from cantor2.suse.de ([195.135.220.15]:48334 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752133Ab3ISJkd (ORCPT ); Thu, 19 Sep 2013 05:40:33 -0400 Date: Thu, 19 Sep 2013 10:40:30 +0100 From: Mel Gorman To: "Darrick J. Wong" , Kent Overstreet Cc: Jens Axboe , Jan Kara , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: Did immutable bvecs accidentally break stable page writes? Message-ID: <20130919094030.GT22421@suse.de> References: <20130919093250.GS22421@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20130919093250.GS22421@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 19, 2013 at 10:32:50AM +0100, Mel Gorman wrote: > Commit ffecfd1a (block: optionally snapshot page contents to provide > stable pages during write) uses bounce buffers for stable page writes in > jbd and ext3. Simplistically, __blk_queue_bounce takes a force parameter > that is used when pages must be snapshot. > > Commit 6bc454d1 (bounce: Refactor __blk_queue_bounce to not use > bi_io_vec) refactored __blk_queue_bounce and now the start of the > function looks like this > > static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig, > mempool_t *pool, int force) > { > struct bio *bio; > int rw = bio_data_dir(*bio_orig); > struct bio_vec *to, *from; > unsigned i; > > bio_for_each_segment(from, *bio_orig, i) > if (page_to_pfn(from->bv_page) > queue_bounce_pfn(q)) > goto bounce; > > return; > bounce: > bio = bio_clone_bioset(*bio_orig, GFP_NOIO, fs_bio_set); > > bio_for_each_segment_all(to, bio, i) { > struct page *page = to->bv_page; > > if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force) > continue; > > Note that the first bio_for_each_segment is completely ignoring the > force parameter and hence snapshotting. This is particularly problematic > for ext3 which forces the use of MS_SNAP_STABLE. > Which of course is no longer a problem for ext3 after commit 71368511 ("mm: make snapshotting pages for stable writes a per-bio operation). The folly of looking at a commit in isolation! I'm still curious why the force parameter is ignored when stable writes are required though. -- Mel Gorman SUSE Labs