Messages in this thread | | | Date | Fri, 8 May 2015 10:11:15 -0700 | From | Zach Brown <> | Subject | Re: [PATCH RFC] vfs: add a O_NOMTIME flag |
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On Thu, May 07, 2015 at 06:01:23PM -0700, Sage Weil wrote: > On Thu, 7 May 2015, 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: > > > > 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? > > I think this is the fundamental question: who do we give the ammunition > to, the user or app writer, or the sysadmin?
Yeah, I think this is right. Dave doesn't want the possibility of it bleeding in to installations through irresponsible default use in apps without explicit buy-in from the people responsible for the backups.
> [...] > > Or, we can be conservative and require a mount option so that the admin > has to explicitly allow behavior that might break some existing > assumptions about mtime/ctime ('-o user_noatime' I guess?). > > I'm happy either way, so long as in the end an unprivileged ceph daemon > avoids the useless work. In our case we always own the entire mount/disk, > so a mount option is just fine.
It seems that the thread has headed towards responding to my suggestion of a possible mount option with an enthusiastic "yes, please, no surprises."
So I'll try that.
- z
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