From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754930Ab1KUKAK (ORCPT ); Mon, 21 Nov 2011 05:00:10 -0500 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:39122 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752063Ab1KUKAI (ORCPT ); Mon, 21 Nov 2011 05:00:08 -0500 Date: Mon, 21 Nov 2011 05:00:04 -0500 From: Christoph Hellwig To: Wu Fengguang Cc: Andrew Morton , Linux Memory Management List , linux-fsdevel@vger.kernel.org, Li Shaohua , Clemens Ladisch , Jens Axboe , Rik van Riel , LKML , Andi Kleen Subject: Re: [PATCH 1/8] block: limit default readahead size for small devices Message-ID: <20111121100004.GB5084@infradead.org> References: <20111121091819.394895091@intel.com> <20111121093846.121502745@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111121093846.121502745@intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 21, 2011 at 05:18:20PM +0800, Wu Fengguang wrote: > This looks reasonable: smaller device tend to be slower (USB sticks as > well as micro/mobile/old hard disks). > > Given that the non-rotational attribute is not always reported, we can > take disk size as a max readahead size hint. This patch uses a formula > that generates the following concrete limits: Given that you mentioned the rotational flag and device size in this mail, as well as benchmarking with an intel SSD - did you measure how useful large read ahead sizes still are with highend Flash device that have extremly high read IOP rates?