Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751800AbbGNLoz (ORCPT ); Tue, 14 Jul 2015 07:44:55 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:60866 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751265AbbGNLox (ORCPT ); Tue, 14 Jul 2015 07:44:53 -0400 Date: Tue, 14 Jul 2015 13:44:49 +0200 From: Pavel Machek To: Andy Lutomirski Cc: Richard Weinberger , Zach Brown , Dave Chinner , Alexander Viro , Sage Weil , linux-fsdevel , LKML , "open list:ABI/API" Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag Message-ID: <20150714114448.GA31973@amd> References: <1430949612-21356-1-git-send-email-zab@redhat.com> <20150507002617.GJ4327@dastard> <20150507172053.GA659@lenny.home.zabbo.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1893 Lines: 41 On Thu 2015-05-07 12:53:46, Andy Lutomirski wrote: > 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. I'm using unison, and yes, I believe I already seen failures from mmap(). I'd like to see that fixed, and I can test the patches. Thanks, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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/