From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754589Ab1G1BE2 (ORCPT ); Wed, 27 Jul 2011 21:04:28 -0400 Received: from mga01.intel.com ([192.55.52.88]:40204 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752863Ab1G1BEW (ORCPT ); Wed, 27 Jul 2011 21:04:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,279,1309762800"; d="scan'208";a="35313520" Subject: Re: [PATCH]vmscan: add block plug for page reclaim From: Shaohua Li To: Andrew Morton Cc: Jens Axboe , Minchan Kim , "mgorman@suse.de" , linux-mm , lkml In-Reply-To: <20110727164523.c2b1d569.akpm@linux-foundation.org> References: <1311130413.15392.326.camel@sli10-conroe> <1311142253.15392.361.camel@sli10-conroe> <1311144559.15392.366.camel@sli10-conroe> <4E287EC0.4030208@fusionio.com> <1311311695.15392.369.camel@sli10-conroe> <4E2B17A6.6080602@fusionio.com> <20110727164523.c2b1d569.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 28 Jul 2011 09:04:20 +0800 Message-ID: <1311815060.15392.375.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-07-28 at 07:45 +0800, Andrew Morton wrote: > On Sat, 23 Jul 2011 20:49:10 +0200 > Jens Axboe wrote: > > > > I can observe the average request size changes. Before the patch, the > > > average request size is about 90k from iostat (but the variation is > > > big). With the patch, the request size is about 100k and variation is > > > small. > > > > That's a good win right there, imho. > > yup. Reduced CPU consumption on that path isn't terribly exciting IMO, > but improved request size is significant. > > Using an additional 44 bytes of stack on that path is also > significant(ly bad). But we need to fix that problem anyway. One way > we could improve things in mm/vmscan.c is to move the blk_plug into > scan_control then get the scan_control off the stack in some manner. > That's easy for kswapd: allocate one scan_control per kswapd at > startup. Doing it for direct-reclaim would be a bit trickier... unfortunately, the direct-reclaim case is what cares about stack. BTW, the scan_control can be dieted. may_unmap/may_swap/may_writepage can be a bit. swappiness < 100, so can be a char. order <= 11, can be a char. should I do it to cut the size? > And I have the usual maintainability whine. If someone comes up to > vmscan.c and sees it calling blk_start_plug(), how are they supposed to > work out why that call is there? They go look at the blk_start_plug() > definition and it is undocumented. I think we can do better than this? the block plug is a little tricky, we definitely should document it. Jens, if you don't mind, I'll add comments there. Thanks, Shaohua