From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) by kanga.kvack.org (Postfix) with ESMTP id AAF7C6B0035 for ; Thu, 3 Jul 2014 15:00:08 -0400 (EDT) Received: by mail-pa0-f42.google.com with SMTP id lj1so682891pab.1 for ; Thu, 03 Jul 2014 12:00:08 -0700 (PDT) Received: from e23smtp09.au.ibm.com (e23smtp09.au.ibm.com. [202.81.31.142]) by mx.google.com with ESMTPS id k7si1086844pdn.511.2014.07.03.12.00.05 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Thu, 03 Jul 2014 12:00:07 -0700 (PDT) Received: from /spool/local by e23smtp09.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 4 Jul 2014 05:00:03 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id DBE742CE8040 for ; Fri, 4 Jul 2014 05:00:00 +1000 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s63IhS4O52428940 for ; Fri, 4 Jul 2014 04:43:28 +1000 Received: from d23av03.au.ibm.com (localhost [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s63IxxTG025442 for ; Fri, 4 Jul 2014 05:00:00 +1000 Message-ID: <53B5A769.5030108@linux.vnet.ibm.com> Date: Fri, 04 Jul 2014 00:26:41 +0530 From: Raghavendra K T MIME-Version: 1.0 Subject: Re: [PATCH] mm readahead: Fix sys_readahead breakage by reverting 2MB limit (bug 79111) References: <1404392547-11648-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <53B59CB5.9060004@linux.vnet.ibm.com> <53B5A343.4090402@linux.vnet.ibm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Andrew Morton , Fengguang Wu , David Cohen , Al Viro , Damien Ramonda , Jan Kara , David Rientjes , Nishanth Aravamudan , linux-mm , Linux Kernel Mailing List On 07/04/2014 12:23 AM, Linus Torvalds wrote: > On Thu, Jul 3, 2014 at 11:38 AM, Raghavendra K T > wrote: >> >> Okay, how about something like 256MB? I would be happy to send a patch >> for that change. > > I'd like to see some performance numbers. I know at least Fedora uses > "readahead()" in the startup scripts, do we have any performance > numbers for that? > > Also, I think 256MB is actually excessive. People still do have really > slow devices out there. USB-2 is still common, and drives that read at > 15MB/s are not unusual. Do we really want to do readahead() that can > take tens of seconds (and *will* take tens of seconds sycnhronously, > because the IO requests fill up). > > So I wouldn't go from 2 to 256. That seems like an excessive jump. I > was more thinking in the 4-8MB range. But even then, I think we should > always have technical reasons (ie preferably numbers) for the change, > not just randomly change it. Okay. I 'll take some time to do the analysis. I think we also should keep in mind of possible remote readahead that would cause unnecessary penalty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org