From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757283AbZEHDZI (ORCPT ); Thu, 7 May 2009 23:25:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754576AbZEHDYz (ORCPT ); Thu, 7 May 2009 23:24:55 -0400 Received: from hera.cwi.nl ([192.16.191.8]:49155 "EHLO hera.cwi.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754116AbZEHDYz (ORCPT ); Thu, 7 May 2009 23:24:55 -0400 Date: Fri, 8 May 2009 05:23:20 +0200 From: "Andries E. Brouwer" To: KAMEZAWA Hiroyuki Cc: "Andries E. Brouwer" , linux-kernel@vger.kernel.org Subject: Re: madvise failure Message-ID: <20090508032315.GA19186@ub> References: <20090507121012.GA17048@ub> <20090508100745.6ef9fe3c.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090508100745.6ef9fe3c.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 08, 2009 at 10:07:45AM +0900, KAMEZAWA Hiroyuki wrote: > "Andries E. Brouwer" wrote: > >> In an application something like >> p = mmap(0, sz, PROT_READ, MAP_PRIVATE, fd, 0); >> madvise(p, sz, MADV_SEQUENTIAL); >> is done for a small number of files, each with a size of a few GB. >> A single sequential pass is done over these files - essentially a merge. >> >> On an old machine the madvise is useful, and decreases total time. > With the same kernel (Ubuntu/2.6.27) ? old one ? Both Ubuntu/2.6.27: 2.6.27-11-generic (new) vs 2.6.27-11-server (old) >> But on a more recent machine, with more memory, the madvise makes >> things worse. There, it seems better not to reveal to the kernel >> that the data will be read sequentially. >> >> Timing (six files of 4GB each, quadcore Intel Q9550, 16GB memory, >> kernel 2.6.27 [Ubuntu], two other processes active): >> with madvise, 7 runs: real time varying 9m10s - 37m29s, >> without madvise, 6 runs: real time fairly constant 5m45s - 5m54s. > Accessing each page one by one sequentially ? Yes. Essentially a merge. > or Sequential but (may) skip some pages in each access ? No. Andries