Re: [PATCH 1/2] xfs: expose the number of free zones in sysfs

[Niklas Cassel <cassel@kernel.org>]

On Thu, Apr 23, 2026 at 07:11:42AM +0200, Christoph Hellwig wrote:
> On Wed, Apr 22, 2026 at 12:29:14PM +0200, Niklas Cassel wrote:
> > You say that the usual way to expose stats is through 2)
> > but e.g. nr_open_zones is exposed via 1), introduced in commit
> > 62c89988dc19 ("xfs: expose the number of open zones in sysfs")
> > (You are the author of that commit btw :))
> 
> nr_open_zones is important for applications as it tells them how many
> different placement points we can have.  nr_free is really just
> an implementation detail.

The commit message for 62c89988dc19 ("xfs: expose the number of open zones
in sysfs") motivated the change by saying that nr_open_zones could be used
in monitoring or testing software.

Which seemed like the same reason/purpose why I wanted to add nr_free_zones.

Your commit message did not mention that user space software could also use
nr_open_zones to calculate the number of different placement points.

Anyway, I can continue with the current (somewhat fragile) way of parsing
/proc/<pid>/mountstats. It is just a bit unfortunate that you can't get it
for a specific mountpoint only.

The "mountstats" command:
https://man7.org/linux/man-pages/man8/mountstats.8.html
seems to be able to display the mountstats for a specific mountpoint only,
but it seems to be for NFS only.

Carlos,
please disregard this series.


Kind regards,
Niklas