From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 9E9766B008A for ; Tue, 14 Dec 2010 09:33:48 -0500 (EST) Date: Tue, 14 Dec 2010 22:33:25 +0800 From: Wu Fengguang Subject: Re: [PATCH 04/35] writeback: reduce per-bdi dirty threshold ramp up time Message-ID: <20101214143325.GA22764@localhost> References: <20101213144646.341970461@intel.com> <20101213150326.856922289@intel.com> <1292333854.2019.16.camel@castor.rsk> <20101214135910.GA21401@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101214135910.GA21401@localhost> Sender: owner-linux-mm@kvack.org To: Richard Kennedy Cc: Andrew Morton , Jan Kara , Peter Zijlstra , Christoph Hellwig , Trond Myklebust , Dave Chinner , Theodore Ts'o , Chris Mason , Mel Gorman , Rik van Riel , KOSAKI Motohiro , Greg Thelen , Minchan Kim , linux-mm , "linux-fsdevel@vger.kernel.org" , LKML List-ID: On Tue, Dec 14, 2010 at 09:59:10PM +0800, Wu Fengguang wrote: > On Tue, Dec 14, 2010 at 09:37:34PM +0800, Richard Kennedy wrote: > > As to the ramp up time, when writing to 2 disks at the same time I see > > the per_bdi_threshold taking up to 20 seconds to converge on a steady > > value after one of the write stops. So I think this could be speeded up > > even more, at least on my setup. > > I have the roughly same ramp up time on the 1-disk 3GB mem test: > > http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/dirty-pages.png > Interestingly, the above graph shows that after about 10s fast ramp up, there is another 20s slow ramp down. It's obviously due the decline of global limit: http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/vmstat-dirty.png But why is the global limit declining? The following log shows that nr_file_pages keeps growing and goes stable after 75 seconds (so long time!). In the same period nr_free_pages goes slowly down to its stable value. Given that the global limit is mainly derived from nr_free_pages+nr_file_pages (I disabled swap), something must be slowly eating memory until 75 ms. Maybe the tracing ring buffers? free file reclaimable pages 50s 369324 + 318760 => 688084 60s 235989 + 448096 => 684085 http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/tests/3G/ext4-1dd-1M-8p-2952M-2.6.37-rc5+-2010-12-09-00-37/vmstat Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org