Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756773Ab2JZHUO (ORCPT ); Fri, 26 Oct 2012 03:20:14 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:57639 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756600Ab2JZHUJ (ORCPT ); Fri, 26 Oct 2012 03:20:09 -0400 Message-ID: <508A399D.6000506@gmail.com> Date: Fri, 26 Oct 2012 15:19:57 +0800 From: Ni zhan Chen User-Agent: Mozilla/5.0 (X11; Linux i686; rv:16.0) Gecko/20121011 Thunderbird/16.0.1 MIME-Version: 1.0 To: Fengguang Wu CC: Dave Chinner , YingHang Zhu , akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state References: <20121025015014.GC29378@dastard> <50889FF1.9030107@gmail.com> <20121025025826.GB23462@localhost> <20121026002544.GI29378@dastard> <20121026012758.GA6282@localhost> <5089F5AD.5040708@gmail.com> <20121026065855.GA9179@localhost> <508A35B0.30106@gmail.com> <20121026070936.GA12282@localhost> In-Reply-To: <20121026070936.GA12282@localhost> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1549 Lines: 43 On 10/26/2012 03:09 PM, Fengguang Wu wrote: > On Fri, Oct 26, 2012 at 03:03:12PM +0800, Ni zhan Chen wrote: >> On 10/26/2012 02:58 PM, Fengguang Wu wrote: >>>> static void shrink_readahead_size_eio(struct file *filp, >>>> struct file_ra_state *ra) >>>> { >>>> - ra->ra_pages /= 4; >>>> + spin_lock(&filp->f_lock); >>>> + filp->f_mode |= FMODE_RANDOM; >>>> + spin_unlock(&filp->f_lock); >>>> >>>> As the example in comment above this function, the read maybe still >>>> sequential, and it will waste IO bandwith if modify to FMODE_RANDOM >>>> directly. >>> Yes immediately disabling readahead may hurt IO performance, the >>> original '/ 4' may perform better when there are only 1-3 IO errors >>> encountered. >> Hi Fengguang, >> >> Why the number should be 1-3? > The original behavior is '/= 4' on each error. > > After 1 errors, readahead size will be shrinked by 1/4 > After 2 errors, readahead size will be shrinked by 1/16 > After 3 errors, readahead size will be shrinked by 1/64 > After 4 errors, readahead size will be effectively 0 (disabled) But from function shrink_readahead_size_eio and its caller filemap_fault I can't find the behavior you mentioned. How you figure out it? Regards, Chen > > Thanks, > Fengguang > -- 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/