Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752995AbZI0QzL (ORCPT ); Sun, 27 Sep 2009 12:55:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751513AbZI0QzL (ORCPT ); Sun, 27 Sep 2009 12:55:11 -0400 Received: from brick.kernel.dk ([93.163.65.50]:49674 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751431AbZI0QzK (ORCPT ); Sun, 27 Sep 2009 12:55:10 -0400 Date: Sun, 27 Sep 2009 18:55:14 +0200 From: Jens Axboe To: Andrew Morton Cc: Chris Mason , linux-kernel@vger.kernel.org, jack@suse.cz Subject: Re: [PATCH] bdi_sync_writeback should WB_SYNC_NONE first Message-ID: <20090927165513.GC23126@kernel.dk> References: <20090925141014.GB15853@think> <20090927013458.53e43459.akpm@linux-foundation.org> <20090927164431.GB23126@kernel.dk> <20090927095202.717fdf64.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090927095202.717fdf64.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2131 Lines: 56 On Sun, Sep 27 2009, Andrew Morton wrote: > On Sun, 27 Sep 2009 18:44:32 +0200 Jens Axboe wrote: > > > On Sun, Sep 27 2009, Andrew Morton wrote: > > > On Fri, 25 Sep 2009 10:10:14 -0400 Chris Mason wrote: > > > > > > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > > > > index 8e1e5e1..27f8e0e 100644 > > > > --- a/fs/fs-writeback.c > > > > +++ b/fs/fs-writeback.c > > > > @@ -225,7 +225,7 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, > > > > { > > > > struct wb_writeback_args args = { > > > > .sb = sb, > > > > - .sync_mode = WB_SYNC_ALL, > > > > + .sync_mode = WB_SYNC_NONE, > > > > .nr_pages = LONG_MAX, > > > > .range_cyclic = 0, > > > > }; > > > > @@ -236,6 +236,13 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, > > > > > > > > bdi_queue_work(bdi, &work); > > > > bdi_wait_on_work_clear(&work); > > > > + > > > > + args.sync_mode = WB_SYNC_ALL; > > > > + args.nr_pages = LONG_MAX; > > > > + > > > > + work.state = WS_USED | WS_ONSTACK; > > > > + bdi_queue_work(bdi, &work); > > > > + bdi_wait_on_work_clear(&work); > > > > } > > > > > > Those LONG_MAX's are a worry. What prevents a very long > > > almost-livelock from occurring if userspace is concurrently dirtying > > > pagecache at a high rate? > > > > Not sure whether Chris' system is back up again, but I discussed this > > with him on irc. Since the WB_SYNC_ALL writeback should be queued behind > > the WB_SYNC_NONE that the non-wait sync already issued, not sure why > > this patch makes a difference. It's definitely not the right approach. > > > > I wasn't referring to this patch actually. The code as it stands in > Linus's tree right now attempts to write back up to 2^63 pages... I agree, it could make the fs sync take a looong time. This is not a new issue, though. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/