From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx183.postini.com [74.125.245.183]) by kanga.kvack.org (Postfix) with SMTP id 2D39E6B0031 for ; Thu, 8 Aug 2013 18:58:42 -0400 (EDT) Message-ID: <5204229F.8000507@intel.com> Date: Thu, 08 Aug 2013 15:58:39 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [RFC 0/3] Add madvise(..., MADV_WILLWRITE) References: <20130807134058.GC12843@quack.suse.cz> <520286A4.1020101@intel.com> <20130808101807.GB4325@quack.suse.cz> <20130808185340.GA13926@quack.suse.cz> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: Jan Kara , linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org I was coincidentally tracking down what I thought was a scalability problem (turned out to be full disks :). I noticed, though, that ext4 is about 20% slower than ext2/3 at doing write page faults (x-axis is number of tasks): http://www.sr71.net/~dave/intel/page-fault-exts/cmp.html?1=ext3&2=ext4&hide=linear,threads,threads_idle,processes_idle&rollPeriod=5 The test case is: https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault3.c A 'perf diff' shows some of the same suspects that you've been talking about, Andy: http://www.sr71.net/~dave/intel/page-fault-exts/diffprofile.txt > 2.39% +2.34% [kernel.kallsyms] [k] __set_page_dirty_buffers > +2.50% [kernel.kallsyms] [k] __block_write_begin > +2.16% [kernel.kallsyms] [k] __block_commit_write The same test on ext4 but doing MAP_PRIVATE instead of MAP_SHARED goes at the same speed as ext2/3: https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault2.c This is looking to me more like an ext4-specific problem that needs to get solved rather than through some interfaces (like MADV_WILLWRITE). -- 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