From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zach Brown Subject: Re: [PATCH RFC] vfs: add a O_NOMTIME flag Date: Thu, 7 May 2015 11:43:50 -0700 Message-ID: <20150507184350.GA1945@lenny.home.zabbo.net> 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 Cc: Alexander Viro , Sage Weil , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org To: Dave Chinner Return-path: Content-Disposition: inline In-Reply-To: <20150507172053.GA659@lenny.home.zabbo.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org > > > The criteria for using O_NOMTIME is the same as for using O_NOATIME: > > > owning the file or having the CAP_FOWNER capability. If we're not > > > comfortable allowing owners to prevent mtime/ctime updates then we > > > should add a tunable to allow O_NOMTIME. Maybe a mount option? > > > > I dislike "turn off safety for performance" options because Joe > > SpeedRacer will always select performance over safety. > > Well, for ceph there's no safety concern. They never use cmtime in > these files. > > So are you suggesting not implementing this and making them rework their > IO paths to avoid the fs maintaining mtime so that we don't give Joe > Speedracer more rope? Or are we talking about adding some speed bumps > that ceph can flip on that might give Joe Speedracer pause? Maybe one way to make it less of an attractive nuisance would be to hide it under open_by_handle_at(). Like xfs_open_by_handle() does today but we probably don't want to unconditionally add it to the generic path so we'd have a flag. They want to move to opening by handles anyway to avoid dirent lookups when opening cold files. - z