From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756157AbZFWIzR (ORCPT ); Tue, 23 Jun 2009 04:55:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751501AbZFWIzE (ORCPT ); Tue, 23 Jun 2009 04:55:04 -0400 Received: from brick.kernel.dk ([93.163.65.50]:45012 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454AbZFWIzD (ORCPT ); Tue, 23 Jun 2009 04:55:03 -0400 Date: Tue, 23 Jun 2009 10:55:05 +0200 From: Jens Axboe To: Andrew Morton Cc: Linus Torvalds , Linux Kernel , hch@infradead.org Subject: Re: merging the per-bdi writeback patchset Message-ID: <20090623085505.GU31415@kernel.dk> References: <20090623081156.GT31415@kernel.dk> <20090623014835.1fc8fb14.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090623014835.1fc8fb14.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 23 2009, Andrew Morton wrote: > On Tue, 23 Jun 2009 10:11:56 +0200 Jens Axboe wrote: > > > Things are looking good for this patchset and it's been in -next for > > almost a week without any reports of problems. So I'd like to merge it > > for 2.6.31 if at all possible. Any objections? > > erk. I was rather expecting I'd have time to have a look at it all. OK, we can wait if we have to, just trying to avoid having to keep this fresh for one full cycle. I have posted this patchset 11 times though over months, so it's not like it's a new piece of work :-) > It's unclear to me actually _why_ the performance changes which were > observed have actually occurred. In fact it's a bit unclear (to me) > why the patchset was written and what it sets out to achieve :( It started out trying to get rid of the pdflush uneven writeout. If you look at various pdflush intensive workloads, even on a single disk you often have 5 or more pdflush threads working the same device. It's just not optimal. Another issue was starvation with request allocation. Given that pdflush does non-blocking writes (it has to, by design), pdflush can potentially be starved if someone else is working the device. > A long time ago the XFS guys (Dave Chinner iirc) said that XFS needs > more than one thread per device to keep the device saturated. Did that > get addressed? It supports up to 32-threads per device, but Chinner et all have been silent. So the support is there and there's a super_operations->inode_get_wb() to map a dirty inode to a writeback device. Nobody is doing that yet though. > (kthread_run() returns an ERR_PTR() on error, btw - not NULL.) Oh thanks, will fix that up. -- Jens Axboe