From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759125AbZFWPCN (ORCPT ); Tue, 23 Jun 2009 11:02:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759917AbZFWPBv (ORCPT ); Tue, 23 Jun 2009 11:01:51 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:51191 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760052AbZFWPBv (ORCPT ); Tue, 23 Jun 2009 11:01:51 -0400 Date: Tue, 23 Jun 2009 08:01:37 -0700 From: Andrew Morton To: Jens Axboe Cc: Linus Torvalds , Linux Kernel , hch@infradead.org Subject: Re: merging the per-bdi writeback patchset Message-Id: <20090623080137.33cdc45c.akpm@linux-foundation.org> In-Reply-To: <20090623085505.GU31415@kernel.dk> References: <20090623081156.GT31415@kernel.dk> <20090623014835.1fc8fb14.akpm@linux-foundation.org> <20090623085505.GU31415@kernel.dk> 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 On Tue, 23 Jun 2009 10:55:05 +0200 Jens Axboe wrote: > 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 :-) Yeah, sorry. > > 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. That's a bug, isn't it? This /* Is another pdflush already flushing this queue? */ if (current_is_pdflush() && !writeback_acquire(bdi)) break; isn't working. > 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. hm, true. 100% starved, or just "slowed down"? The latter I trust - otherwise there are still failure modes? > > 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. OK. How many kernel threads do the 1000-spindle people end up with?