From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 970716B004D for ; Sat, 10 Oct 2009 21:10:17 -0400 (EDT) Date: Sun, 11 Oct 2009 09:10:06 +0800 From: Wu Fengguang Subject: Re: [PATCH] mm: make VM_MAX_READAHEAD configurable Message-ID: <20091011011006.GA20205@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091009154950.43f01784@mschwide.boeblingen.de.ibm.com> Sender: owner-linux-mm@kvack.org To: Martin Schwidefsky Cc: Jens Axboe , Peter Zijlstra , Ehrhardt Christian , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Andrew Morton List-ID: Hi Martin, On Fri, Oct 09, 2009 at 09:49:50PM +0800, Martin Schwidefsky wrote: > On Fri, 9 Oct 2009 14:29:52 +0200 > Jens Axboe wrote: > > > On Fri, Oct 09 2009, Peter Zijlstra wrote: > > > On Fri, 2009-10-09 at 13:19 +0200, Ehrhardt Christian wrote: > > > > From: Christian Ehrhardt > > > > > > > > On one hand the define VM_MAX_READAHEAD in include/linux/mm.h is just a default > > > > and can be configured per block device queue. > > > > On the other hand a lot of admins do not use it, therefore it is reasonable to > > > > set a wise default. > > > > > > > > This path allows to configure the value via Kconfig mechanisms and therefore > > > > allow the assignment of different defaults dependent on other Kconfig symbols. > > > > > > > > Using this, the patch increases the default max readahead for s390 improving > > > > sequential throughput in a lot of scenarios with almost no drawbacks (only > > > > theoretical workloads with a lot concurrent sequential read patterns on a very > > > > low memory system suffer due to page cache trashing as expected). [snip] > > The patch from Christian fixes a performance regression in the latest > distributions for s390. So we would opt for a larger value, 512KB seems > to be a good one. I have no idea what that will do to the embedded > space which is why Christian choose to make it configurable. Clearly > the better solution would be some sort of system control that can be > modified at runtime. 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..) 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