From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f175.google.com (mail-ve0-f175.google.com [209.85.128.175]) by kanga.kvack.org (Postfix) with ESMTP id 893846B0035 for ; Thu, 3 Jul 2014 14:53:59 -0400 (EDT) Received: by mail-ve0-f175.google.com with SMTP id jx11so676804veb.6 for ; Thu, 03 Jul 2014 11:53:59 -0700 (PDT) Received: from mail-vc0-x22c.google.com (mail-vc0-x22c.google.com [2607:f8b0:400c:c03::22c]) by mx.google.com with ESMTPS id sq3si6041110vdb.76.2014.07.03.11.53.58 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 03 Jul 2014 11:53:58 -0700 (PDT) Received: by mail-vc0-f172.google.com with SMTP id hy10so651147vcb.31 for ; Thu, 03 Jul 2014 11:53:57 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <53B5A343.4090402@linux.vnet.ibm.com> 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> Date: Thu, 3 Jul 2014 11:53:57 -0700 Message-ID: Subject: Re: [PATCH] mm readahead: Fix sys_readahead breakage by reverting 2MB limit (bug 79111) From: Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Raghavendra K T Cc: Andrew Morton , Fengguang Wu , David Cohen , Al Viro , Damien Ramonda , Jan Kara , David Rientjes , Nishanth Aravamudan , linux-mm , Linux Kernel Mailing List 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. Linus -- 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