Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757292Ab2JZINi (ORCPT ); Fri, 26 Oct 2012 04:13:38 -0400 Received: from mail-ia0-f174.google.com ([209.85.210.174]:47415 "EHLO mail-ia0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757210Ab2JZINd (ORCPT ); Fri, 26 Oct 2012 04:13:33 -0400 MIME-Version: 1.0 In-Reply-To: <20121026080240.GA13662@localhost> References: <20121025025826.GB23462@localhost> <20121026002544.GI29378@dastard> <20121026012758.GA6282@localhost> <5089F5AD.5040708@gmail.com> <20121026065855.GA9179@localhost> <508A35B0.30106@gmail.com> <20121026070936.GA12282@localhost> <508A399D.6000506@gmail.com> <20121026073630.GA12886@localhost> <508A4007.5080906@gmail.com> <20121026080240.GA13662@localhost> Date: Fri, 26 Oct 2012 16:13:32 +0800 Message-ID: Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state From: YingHang Zhu To: Fengguang Wu Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Chinner , linux-mm@kvack.org, Ni zhan Chen Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2894 Lines: 70 Hi Fengguang, On Fri, Oct 26, 2012 at 4:02 PM, Fengguang Wu wrote: > On Fri, Oct 26, 2012 at 03:47:19PM +0800, Ni zhan Chen wrote: >> On 10/26/2012 03:36 PM, Fengguang Wu wrote: >> >On Fri, Oct 26, 2012 at 03:19:57PM +0800, Ni zhan Chen wrote: >> >>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? >> >It's this line in shrink_readahead_size_eio(): >> > >> > ra->ra_pages /= 4; >> >> Yeah, I mean why the 4th readahead size will be 0(disabled)? What's >> the original value of ra->ra_pages? How can guarantee the 4th shrink >> readahead size can be 0? > > Ah OK, I'm talking about the typical case. The default readahead size > is 128k, which will become 0 after / 256. The reasonable good ra size > for hard disks is 1MB=256pages, which also becomes 1page after 4 errors. How do you feel about my previous mail of error statistics, in fact I prefer treating these files independently, so do some check for FMODE_RANDOM before we change the readahead window to avoid trashing the read ahead window, If the user applications call fadvise but the media turn out to be error-prone, after one read we know the situation and set the file in FMODE_RANDOM, this should solve the issue Dave raised. Do I miss something? Thanks in advance. > > Thanks, > Fengguang -- Thanks, Ying Zhu -- 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/