Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751652AbbEGTyL (ORCPT ); Thu, 7 May 2015 15:54:11 -0400 Received: from mail-la0-f53.google.com ([209.85.215.53]:33624 "EHLO mail-la0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751294AbbEGTyI (ORCPT ); Thu, 7 May 2015 15:54:08 -0400 MIME-Version: 1.0 In-Reply-To: References: <1430949612-21356-1-git-send-email-zab@redhat.com> <20150507002617.GJ4327@dastard> <20150507172053.GA659@lenny.home.zabbo.net> From: Andy Lutomirski Date: Thu, 7 May 2015 12:53:46 -0700 Message-ID: Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag To: Richard Weinberger Cc: Zach Brown , Dave Chinner , Alexander Viro , Sage Weil , linux-fsdevel , LKML , "open list:ABI/API" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1507 Lines: 33 On Thu, May 7, 2015 at 12:09 PM, Richard Weinberger wrote: > On Thu, May 7, 2015 at 7:20 PM, Zach Brown wrote: >> On Thu, May 07, 2015 at 10:26:17AM +1000, Dave Chinner wrote: >>> On Wed, May 06, 2015 at 03:00:12PM -0700, Zach Brown wrote: >>> > Add the O_NOMTIME flag which prevents mtime from being updated which can >>> > greatly reduce the IO overhead of writes to allocated and initialized >>> > regions of files. >>> >>> Hmmm. How do backup programs now work out if the file has changed >>> and hence needs copying again? ie. applications using this will >>> break other critical infrastructure in subtle ways. >> >> By using backup infrastructure that doesn't use cmtime. Like btrfs >> send/recv. Or application level backups that know how to do >> incrementals from metadata in giant database files, say, without >> walking, comparing, and copying the entire thing. > > But how can Joey random user know that some of his > applications are using O_NOMTIME and his KISS backup > program does no longer function as expected? > Joey random user can't have a working KISS backup anyway, though, because we screw up mtime updates on mmap writes. I have patches gathering dust that fix that, though. --Andy -- 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/