From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 0EFAE6B004D for ; Mon, 12 Oct 2009 05:39:24 -0400 (EDT) Date: Mon, 12 Oct 2009 17:39:21 +0800 From: Wu Fengguang Subject: Re: [PATCH] mm: make VM_MAX_READAHEAD configurable Message-ID: <20091012093920.GA2480@localhost> References: <1255087175-21200-1-git-send-email-ehrhardt@linux.vnet.ibm.com> <1255090830.8802.60.camel@laptop> <20091009122952.GI9228@kernel.dk> <20091009154950.43f01784@mschwide.boeblingen.de.ibm.com> <20091011011006.GA20205@localhost> <4AD2C43D.1080804@linux.vnet.ibm.com> <20091012062317.GA10719@localhost> <4AD2F70C.4010506@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AD2F70C.4010506@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org To: Christian Ehrhardt Cc: Martin Schwidefsky , Jens Axboe , Peter Zijlstra , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton List-ID: On Mon, Oct 12, 2009 at 05:29:48PM +0800, Christian Ehrhardt wrote: > Wu Fengguang wrote: > > [SNIP] > >>> May I ask for more details about your performance regression and why > >>> it is related to readahead size? (we didn't change VM_MAX_READAHEAD..) > >>> > >>> > >> Sure, the performance regression appeared when comparing Novell SLES10 > >> vs. SLES11. > >> While you are right Wu that the upstream default never changed so far, > >> SLES10 had a > >> patch applied that set 512. > >> > > > > I see. I'm curious why SLES11 removed that patch. Did it experienced > > some regressions with the larger readahead size? > > > > > > Only the obvious expected one with very low free/cacheable > memory and a lot of parallel processes that do sequential I/O. > The RA size scales up for all of them but 64xMaxRA then > doesn't fit. > > For example iozone with 64 threads (each on one disk for its own), > sequential access pattern read with I guess 10 M free for cache > suffered by ~15% due to trashing. FYI, I just finished with a patch for dealing with readahead thrashing. Will do some tests and post the result :) 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/ . Don't email: email@kvack.org