On Tue 15-05-12 08:35:50, J. Bruce Fields wrote:
> On Tue, May 15, 2012 at 12:30:21PM +0200, Jan Kara wrote:
> > On Mon 14-05-12 19:54:32, J. Bruce Fields wrote:
> > > On Mon, May 14, 2012 at 05:33:04PM -0600, Andreas Dilger wrote:
> > > > I said as much in another reply - that once i_version is used on
> > > > a filesystem, it should be made "sticky" (i.e. permanently enabled
> > > > for that filesystem). However, until that time it shouldn't be
> > > > enabled just because it might one day be used.
> > > >
> > > > Even better than just blindly bumping the i_version on every change,
> > > > it would be better to have users of i_version (i.e. knfsd) flag the
> > > > inode with "needs i_version update" then read the version. When the
> > > > filesystem/VFS bumps i_version the next time it can clear this flag
> > > > and not update i_version again until after the next time i_version
> > > > is actually used.
> > >
> > > I really don't want to do anything more complicated than necessary.
> > >
> > > What would be the worst-case test for the extra inode dirtying, so we
> > > can see what the numbers actually are?
> > Something like:
> >
> > int fd, i;
> > struct timeval tv[2];
> >
> > fd = open("file", O_CREAT | O_RDWR, 0644);
> > if (fd < 0)
> > return 1;
> > for (i = 0; i < 1000000; i++) {
> > gettimeofday(tv);
> > tv[1] = tv[0];
> > if (futimes(fd, tv) < 0)
> > return 1;
> > }
> > return 0;
> >
> > And see how long does it take with and without i_version?
>
> The complaint I hear from Andreas is that we'll cause file_update_time()
> to call mark_inode_dirty() more often.
>
> I don't believe futimes() calls file_update_time().
Yeah, right. I didn't check and I was wrong...
> So maybe replace that futimes() by a one-byte write?
Yes, "pwrite(fd, "data", 1, 0);" should be then a proper test instead of
futimes().
Honza
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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