From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754229Ab1KXW23 (ORCPT ); Thu, 24 Nov 2011 17:28:29 -0500 Received: from cantor2.suse.de ([195.135.220.15]:37451 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862Ab1KXW21 (ORCPT ); Thu, 24 Nov 2011 17:28:27 -0500 Date: Thu, 24 Nov 2011 23:28:22 +0100 From: Jan Kara To: Wu Fengguang Cc: Christoph Hellwig , Andrew Morton , Linux Memory Management List , "linux-fsdevel@vger.kernel.org" , Ankit Jain , Dave Chinner , Christian Ehrhardt , Rik van Riel , Nikanth Karthikesan , LKML , Andi Kleen Subject: Re: [PATCH 2/8] readahead: make default readahead size a kernel parameter Message-ID: <20111124222822.GG29519@quack.suse.cz> References: <20111121091819.394895091@intel.com> <20111121093846.251104145@intel.com> <20111121100137.GC5084@infradead.org> <20111121113540.GB8895@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111121113540.GB8895@localhost> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 21-11-11 19:35:40, Wu Fengguang wrote: > On Mon, Nov 21, 2011 at 06:01:37PM +0800, Christoph Hellwig wrote: > > On Mon, Nov 21, 2011 at 05:18:21PM +0800, Wu Fengguang wrote: > > > From: Nikanth Karthikesan > > > > > > Add new kernel parameter "readahead=", which allows user to override > > > the static VM_MAX_READAHEAD=128kb. > > > > Is a boot-time paramter really such a good idea? I would at least > > It's most convenient to set at boot time, because the default size > will be used to initialize all the block devices. > > > make it a sysctl so that it's run-time controllable, including > > beeing able to set it from initscripts. > > Once boot up, it's more natural to set the size one by one, for > example > > blockdev --setra 1024 /dev/sda2 > or > echo 512 > /sys/block/sda/queue/read_ahead_kb > > And you still have the chance to modify the global default, but the > change will only be inherited by newly created devices thereafter: > > echo 512 > /sys/devices/virtual/bdi/default/read_ahead_kb > > The above command is very suitable for use in initscripts. However > there are no natural way to do sysctl as there is no such a global > value. Well, you can always have an udev rule to set read_ahead_kb to whatever you want. In some respect that looks like a nicer solution to me... Honza -- Jan Kara SUSE Labs, CR