Re: [PATCH v2 00/11] fs: multigrain timestamp redux

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2024-07-01 at 09:53 -0400, Josef Bacik wrote:
> On Mon, Jul 01, 2024 at 06:26:36AM -0400, Jeff Layton wrote:
> > This set is essentially unchanged from the last one, aside from the
> > new file in Documentation/. I had a review comment from Andi Kleen
> > suggesting that the ctime_floor should be per time_namespace, but I
> > think that's incorrect as the realtime clock is not namespaced.
> > 
> > At LSF/MM this year, we had a discussion about the inode change
> > attribute. At the time I mentioned that I thought I could salvage the
> > multigrain timestamp work that had to be reverted last year [1].  That
> > version had to be reverted because it was possible for a file to get a
> > coarse grained timestamp that appeared to be earlier than another file
> > that had recently gotten a fine-grained stamp.
> > 
> > This version corrects the problem by establishing a per-time_namespace
> > ctime_floor value that should prevent this from occurring. In the above
> > situation that was problematic before, the two files might end up with
> > the same timestamp value, but they won't appear to have been modified in
> > the wrong order.
> > 
> > That problem was discovered by the test-stat-time gnulib test. Note that
> > that test still fails on multigrain timestamps, but that's because its
> > method of determining the minimum delay that will show a timestamp
> > change will no longer work with multigrain timestamps. I have a patch to
> > change the testcase to use a different method that I've posted to the
> > bug-gnulib mailing list.
> > 
> > The big question with this set is whether the performance will be
> > suitable. The testing I've done seems to show performance parity with
> > multigrain timestamps enabled, but it's hard to rule this out regressing
> > some workload.
> > 
> > This set is based on top of Christian's vfs.misc branch (which has the
> > earlier change to track inode timestamps as discrete integers). If there
> > are no major objections, I'd like to let this soak in linux-next for a
> > bit to see if any problems shake out.
> > 
> > [1]: https://lore.kernel.org/linux-fsdevel/20230807-mgctime-v7-0-d1dec143a704@kernel.org/
> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> 
> I have a few nits that need to be addressed, but you can add
> 
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> 
> to the series once they're addressed.  Thanks,
> 

Thanks! Fixed them up in my tree. I left the IS_I_VERSION check out as
well, and added a note to the changelog on the btrfs patch.
-- 
Jeff Layton <jlayton@kernel.org>