From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765124AbZEAUoP (ORCPT ); Fri, 1 May 2009 16:44:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755592AbZEAUn7 (ORCPT ); Fri, 1 May 2009 16:43:59 -0400 Received: from bc.sympatico.ca ([209.226.175.184]:61472 "EHLO tomts22-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755527AbZEAUn6 (ORCPT ); Fri, 1 May 2009 16:43:58 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AugEADD4+klMQW1W/2dsb2JhbACBUM19g30F Date: Fri, 1 May 2009 16:43:55 -0400 From: Mathieu Desnoyers To: Christoph Lameter Cc: Nick Piggin , Peter Zijlstra , Linux Kernel Mailing List , Yuriy Lalym , ltt-dev@lists.casi.polymtl.ca, Tejun Heo , Ingo Molnar , Linus Torvalds , Andrew Morton Subject: Re: [ltt-dev] [PATCH] Fix dirty page accounting in redirty_page_for_writepage() Message-ID: <20090501204355.GB20280@Krystal> References: <20090430141211.GB5922@Krystal> <20090430194158.GB12926@Krystal> <20090430211750.GA19933@Krystal> <20090501192142.GA18339@Krystal> <20090501202400.GA20280@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 16:42:06 up 62 days, 17:08, 2 users, load average: 0.29, 0.53, 0.52 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Christoph Lameter (cl@linux.com) wrote: > On Fri, 1 May 2009, Mathieu Desnoyers wrote: > > > So, back to my original point : do you agree on the usefulness of > > separating fallback irq-disabling from the per-cpu atomic construct ? > > No. Percpu operations are used for statistics and are like atomic > operations. Aggregation of these leads to a can of worms that we better > leave unopened. > > > x86 would map : > > > > percpu_irqsave/restore to "nothing". > > percpu_add_return_irq to xadd instruction. It is irq-safe by design. > > > > Other architectures (fallback) would map > > > > percpu_irqsave/restore to local_irq_save/restore. > > percpu_add_return_irq to var += value; return var; > > Shudder.... We have explored those types of macros before (while doing > fastpath optimization for SLUB) and it significant increases the > complexity. People may add additional instructions in between and now > interrupts off could be on or off depending on the architecture. Sometimes > percpu_irqsave does nothing. Very difficult to ensure that the usage is > correct. > > And we have barely any usage case for such macros. > Then do you have a better idea on how to deal with __inc_zone_state/inc_zone_state without duplicating the code and without adding useless local_irq_save/restore on x86 ? Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68