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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Tue, 5 Jan 2021 17:45:07 +0200
Message-ID: <CAOQ4uxhJA93JeNMHB5-Enhx1t-ZirRHs7MHtL02jhg8DAEz9BA@mail.gmail.com>
Subject: Re: [PATCH 2/2] nfsd: report per-export stats
To:     "J . Bruce Fields" <bfields@fieldses.org>
Cc:     Jeff Layton <jlayton@poochiereds.net>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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On Tue, Jan 5, 2021 at 5:34 PM J . Bruce Fields <bfields@fieldses.org> wrote:
>
> On Tue, Jan 05, 2021 at 08:42:21AM +0200, Amir Goldstein wrote:
> > On Tue, Jan 5, 2021 at 12:49 AM J . Bruce Fields <bfields@fieldses.org> wrote:
> > >
> > > On Mon, Dec 28, 2020 at 07:03:44PM +0200, Amir Goldstein wrote:
> > > > Collect some nfsd stats per export in addition to the global stats.
> > >
> > > Seems like a reasonable thing to do.
> > >
> > > > A new nfsdfs export_stats file is created.  It uses the same ops as the
> > > > exports file to iterate the export entries and we use the file's name to
> > > > determine the reported info per export.  For example:
> > > >
> > > >  $ cat /proc/fs/nfsd/export_stats
> > > >  # Version 1.1
> > > >  # Path Client Start-time
> > > >  #    Stats
> > > >  /test        localhost       92
> > > >       fh_stale: 0
> > > >       io_read: 9
> > > >       io_write: 1
> > > >
> > > > Every export entry reports the start time when stats collection
> > > > started, so stats collecting scripts can know if stats where reset
> > > > between samples.
> > >
> > > Yes, you expect svc_export to be created (or destroyed) when a
> > > filesystem is exported (or unexported), or when nfsd starts (or stops).
> > >
> > > But actually it's just a cache entry and can be removed and recreated at
> > > any time.  Not much we can do about losing statistics when that happens,
> > > but the start time at least gives us some hope of interpreting the
> > > statistics.
> > >
> > > Why weren't there existing file system statistics that would do the job
> > > in your case?
> > >
> >
> > I am not sure what you mean.
> > We want to know the amount of read/write io for a specific export on
> > the server, including io to/from page cache, which isn't counted by stats
> > of most local filesystems.
>
> I was just curious what exactly your use case was.  (And incidentally
> if it explained the interest in STALE errors as well?)

Ah no I don't. I just added it as a public service.
Do you prefer that I drop fh_stale from per-export stats?

>
> > Unrelated, in our search for those statistics, we were surprised (good
> > surprises)
> > to learn about s_op->show_stats(), but also surprised (bad surprise)
> > to learn how few filesystems implement this method.
>
> Yes, Chuck added it for NFS (checks history...) in 2006.  NFS is unique
> in some ways, but I can imagine it'd be useful elsewhere too.
>

Well, we are exporting fuse, so I considered adding ->show_stats() for fuse,
but per export stats is MUCH easier ;-)

Thanks,
Amir.