Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757488Ab0BLRkM (ORCPT ); Fri, 12 Feb 2010 12:40:12 -0500 Received: from waste.org ([173.11.57.241]:47945 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755059Ab0BLRkJ (ORCPT ); Fri, 12 Feb 2010 12:40:09 -0500 Subject: Re: [PATCH 03/11] readahead: bump up the default readahead size From: Matt Mackall To: Jamie Lokier Cc: Wu Fengguang , Christian Ehrhardt , Andrew Morton , Jens Axboe , Chris Mason , Peter Zijlstra , Martin Schwidefsky , Clemens Ladisch , Olivier Galibert , Linux Memory Management List , "linux-fsdevel@vger.kernel.org" , LKML , Paul Gortmaker , David Woodhouse , linux-embedded@vger.kernel.org In-Reply-To: <20100211234249.GE407@shareable.org> References: <20100207041013.891441102@intel.com> <20100207041043.147345346@intel.com> <4B6FBB3F.4010701@linux.vnet.ibm.com> <20100208134634.GA3024@localhost> <1265924254.15603.79.camel@calx> <20100211234249.GE407@shareable.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 11 Feb 2010 18:04:31 -0600 Message-ID: <1265933071.15603.129.camel@calx> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1895 Lines: 43 On Thu, 2010-02-11 at 23:42 +0000, Jamie Lokier wrote: > Matt Mackall wrote: > > On Mon, 2010-02-08 at 21:46 +0800, Wu Fengguang wrote: > > > Chris, > > > > > > Firstly inform the linux-embedded maintainers :) > > > > > > I think it's a good suggestion to add a config option > > > (CONFIG_READAHEAD_SIZE). Will update the patch.. > > > > I don't have a strong opinion here beyond the nagging feeling that we > > should be using a per-bdev scaling window scheme rather than something > > static. > > I agree with both. 100Mb/s isn't typical on little devices, even if a > fast ATA disk is attached. I've got something here where the ATA > interface itself (on a SoC) gets about 10MB/s max when doing nothing > else, or 4MB/s when talking to the network at the same time. > It's not a modern design, but you know, it's junk we try to use :-) > > It sounds like a calculation based on throughput and seek time or IOP > rate, and maybe clamped if memory is small, would be good. > > Is the window size something that could be meaningfully adjusted > according to live measurements? I think so. You've basically got a few different things you want to balance: throughput, latency, and memory pressure. Successful readaheads expand the window, as do empty request queues, while long request queues and memory reclaim events collapse it. With any luck, we'll then automatically do the right thing with fast/slow devices on big/small boxes with varying load. And, like TCP, we don't need to 'know' anything about the hardware, except to watch what happens when we use it. -- http://selenic.com : development and support for Mercurial and Linux -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/