Re: [PATCH 2/2] mkfs: Show progress during block discard

[Pavel Reichl <preichl@redhat.com>]

On Fri, Nov 22, 2019 at 12:42 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Thu, Nov 21, 2019 at 10:44:45PM +0100, Pavel Reichl wrote:
> > Signed-off-by: Pavel Reichl <preichl@redhat.com>
> > ---
> >  mkfs/xfs_mkfs.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> > index a02d6f66..07b8bd78 100644
> > --- a/mkfs/xfs_mkfs.c
> > +++ b/mkfs/xfs_mkfs.c
> > @@ -1248,6 +1248,7 @@ discard_blocks(dev_t dev, uint64_t nsectors)
> >       const uint64_t  step            = (uint64_t)2<<30;
> >       /* Sector size is 512 bytes */
> >       const uint64_t  count           = nsectors << 9;
> > +     uint64_t        prev_done       = (uint64_t) ~0;
> >
> >       fd = libxfs_device_to_fd(dev);
> >       if (fd <= 0)
> > @@ -1255,6 +1256,7 @@ discard_blocks(dev_t dev, uint64_t nsectors)
> >
> >       while (offset < count) {
> >               uint64_t        tmp_step = step;
> > +             uint64_t        done = offset * 100 / count;
>
> That will overflow on a EB-scale (2^60 bytes) filesystems, won't it?

I guess that can happen, sorry. I'll try to come out with computation
based on a floating point arithmetic. There should not be any
performance or actual precision problem.
(well actually I'll drop this line completely, no ratio will be
computed in the end)

>
> >
> >               if ((offset + step) > count)
> >                       tmp_step = count - offset;
> > @@ -1268,7 +1270,13 @@ discard_blocks(dev_t dev, uint64_t nsectors)
> >                       return;
> >
> >               offset += tmp_step;
> > +
> > +             if (prev_done != done) {
> > +                     prev_done = done;
> > +                     fprintf(stderr, _("Discarding: %2lu%% done\n"), done);
> > +             }
> >       }
> > +     fprintf(stderr, _("Discarding is done.\n"));
>
> Hmmm - this output doesn't get suppressed when the "quiet" (-q)
> option is used. mkfs is supposed to be silent when this option is
> specified.

OK, my bad. I'll fix that.
>
> I also suspect that it breaks a few fstests, too, as a some of them
> capture and filter mkfs output. They'll need filters to drop these
> new messages.
>
> FWIW, a 100 lines of extra mkfs output is going to cause workflow
> issues. I know it will cause me problems, because I often mkfs 500TB
> filesystems tens of times a day on a discard enabled device. This
> extra output will scroll all the context of the previous test run
> I'm about to compare against off my terminal screen and so now I
> will have to scroll the terminal to look at the results of
> back-to-back runs. IOWs, I'm going to immediately want to turn this
> output off and have it stay off permanently.
>
> Hence I think that, by default, just outputting a single "Discard in
> progress" line before starting the discard would be sufficient

OK, maybe just one line "Discard in progress" is actually what users
need. The computing of % done was probably just overkill from my side.
Sorry about that.

> indication of what mkfs is currently doing. If someone wants more
> verbose progress output, then we should probably introduce a
> "verbose" CLI option to go along with the "quiet" option that
> suppresses all output.
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>