Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753935AbZIWBsZ (ORCPT ); Tue, 22 Sep 2009 21:48:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753612AbZIWBsY (ORCPT ); Tue, 22 Sep 2009 21:48:24 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:39452 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753823AbZIWBsX (ORCPT ); Tue, 22 Sep 2009 21:48:23 -0400 Date: Tue, 22 Sep 2009 18:47:26 -0700 From: Andrew Morton To: Wu Fengguang Cc: Chris Mason , Peter Zijlstra , "Li, Shaohua" , "linux-kernel@vger.kernel.org" , "richard@rsk.demon.co.uk" , "jens.axboe@oracle.com" Subject: Re: regression in page writeback Message-Id: <20090922184726.b3669515.akpm@linux-foundation.org> In-Reply-To: <20090923013236.GA10885@localhost> References: <1253601612.8439.274.camel@twins> <20090922080505.GB9192@localhost> <1253606965.8439.281.camel@twins> <20090922082427.GA24888@localhost> <1253608335.8439.283.camel@twins> <20090922155259.GL10825@think> <20090923002220.GA6382@localhost> <20090922175452.d66400dd.akpm@linux-foundation.org> <20090923011758.GC6382@localhost> <20090922182832.28e7f73a.akpm@linux-foundation.org> <20090923013236.GA10885@localhost> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2368 Lines: 57 On Wed, 23 Sep 2009 09:32:36 +0800 Wu Fengguang wrote: > On Wed, Sep 23, 2009 at 09:28:32AM +0800, Andrew Morton wrote: > > On Wed, 23 Sep 2009 09:17:58 +0800 Wu Fengguang wrote: > > > > > On Wed, Sep 23, 2009 at 08:54:52AM +0800, Andrew Morton wrote: > > > > On Wed, 23 Sep 2009 08:22:20 +0800 Wu Fengguang wrote: > > > > > > > > > Jens' per-bdi writeback has another improvement. In 2.6.31, when > > > > > superblocks A and B both have 100000 dirty pages, it will first > > > > > exhaust A's 100000 dirty pages before going on to sync B's. > > > > > > > > That would only be true if someone broke 2.6.31. Did they? > > > > > > > > SYSCALL_DEFINE0(sync) > > > > { > > > > wakeup_pdflush(0); > > > > sync_filesystems(0); > > > > sync_filesystems(1); > > > > if (unlikely(laptop_mode)) > > > > laptop_sync_completion(); > > > > return 0; > > > > } > > > > > > > > the sync_filesystems(0) is supposed to non-blockingly start IO against > > > > all devices. It used to do that correctly. But people mucked with it > > > > so perhaps it no longer does. > > > > > > I'm referring to writeback_inodes(). Each invocation of which (to sync > > > 4MB) will do the same iteration over superblocks A => B => C ... So if > > > A has dirty pages, it will always be served first. > > > > > > So if wbc->bdi == NULL (which is true for kupdate/background sync), it > > > will have to first exhaust A before going on to B and C. > > > > But that works OK. We fill the first device's queue, then it gets > > congested and sync_sb_inodes() does nothing and we advance to the next > > queue. > > > > If a device has more than a queue's worth of dirty data then we'll > > probably leave some of that dirty memory un-queued, so there's some > > lack of concurrency in that situation. > > Yes, exactly if block device is not fast enough. Actually, no. If there's still outstanding dirty data for any of those queues, both wb_kupdate() and background_writeout() will take a teeny sleep and then will re-poll the queues. Did that logic get broken? -- 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/