Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756359Ab1DVRJa (ORCPT ); Fri, 22 Apr 2011 13:09:30 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:40586 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756233Ab1DVRJR (ORCPT ); Fri, 22 Apr 2011 13:09:17 -0400 Message-ID: <4DB1B62B.3000700@oracle.com> Date: Fri, 22 Apr 2011 10:08:59 -0700 From: Sunil Mushran User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.14) Gecko/20110223 Lightning/1.0b2 Thunderbird/3.1.8 MIME-Version: 1.0 To: Eric Blake CC: Markus Trippelsdorf , Christoph Hellwig , Josef Bacik , linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK_DATA flags References: <1303414954-3315-1-git-send-email-josef@redhat.com> <20110422045054.GB17795@infradead.org> <20110422112852.GB1627@x4.trippels.de> <4DB16B72.1050702@redhat.com> <4DB1AC9D.3010706@oracle.com> <4DB1AF6F.4040706@redhat.com> <4DB1B37C.9070406@oracle.com> <4DB1B4F1.8070109@redhat.com> In-Reply-To: <4DB1B4F1.8070109@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: acsinet22.oracle.com [141.146.126.238] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090206.4DB1B637.0015:SCFMA922111,ss=1,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1268 Lines: 25 On 04/22/2011 10:03 AM, Eric Blake wrote: >> cp can read whatever blocksize it chooses. If that block contains >> zero, it would signal cp that maybe it should SEEK_DATA and skip >> reading all those blocks. That's all. We are not trying to achieve >> perfection. We are just trying to reduce cpu waste. >> >> If the fs supports SEEK_*, then great. If it does not, then it is no >> worse than before. > But providing just SEEK_DATA _is_ worse than before if you don't provide > the correct SEEK_HOLE everywhere. Because then your algorithm of trying > lseek(SEEK_DATA) after every run of zeros in the hopes of an > optimization is a wasted syscall, since it will just return your current > offset every time, so you end up with more syscalls than if you had used > the single lseek(SEEK_DATA) that returns the end of the file up front, > and known that the remainder of the file has no holes to even try > seeking past. You are over-optimizing. strace any process on your box and you will find numerous wasted syscalls. -- 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/