From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 3D7E26B0087 for ; Fri, 9 Jan 2009 14:08:29 -0500 (EST) Subject: Re: Increase dirty_ratio and dirty_background_ratio? From: Chris Mason In-Reply-To: <20090109180241.GA15023@duck.suse.cz> References: <20090107.125133.214628094.davem@davemloft.net> <20090108030245.e7c8ceaf.akpm@linux-foundation.org> <20090108.082413.156881254.davem@davemloft.net> <1231433701.14304.24.camel@think.oraclecorp.com> <20090108195728.GC14560@duck.suse.cz> <20090109180241.GA15023@duck.suse.cz> Content-Type: text/plain Date: Fri, 09 Jan 2009 14:07:22 -0500 Message-Id: <1231528042.5998.13.camel@think.oraclecorp.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Jan Kara Cc: Linus Torvalds , David Miller , akpm@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, npiggin@suse.de List-ID: On Fri, 2009-01-09 at 19:02 +0100, Jan Kara wrote: > What we observe in the seekwatcher graphs is, that there are three > processes writing back the single database file in parallel (2 pdflush > threads because the machine has 2 CPUs, and the database process itself > because of dirty throttling). Each of the processes is writing back the > file at a different offset and so they together create even more random IO > (I'm attaching the graph and can provide blocktrace data if someone is > interested). If there was just one process doing the writeback, we'd be > writing back those data considerably faster... I spent some time trying similar things for btrfs, and went as far as making my own writeback thread and changing pdflush and throttled writes to wait on it. It was a great hack, but in the end I found the real problem was the way write_cache_pages is advancing the page_index. You probably remember the related ext4 discussion, and you could try my simple patch in this workload to see if it helps ext3. http://lkml.org/lkml/2008/10/1/278 Ext3 may need similar tricks. -chris -- 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/ . Don't email: email@kvack.org