linux-kernel - Re: [PATCH] ceph: show max caps in debugfs caps file

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Date:   Thu, 21 May 2020 20:19:06 +0800
From:   Yanhu Cao <gmayyyha@...il.com>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Ilya Dryomov <idryomov@...il.com>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ceph: show max caps in debugfs caps file

On Thu, May 21, 2020 at 7:09 PM Jeff Layton <jlayton@...nel.org> wrote:
>
> On Thu, 2020-05-21 at 17:38 +0800, Yanhu Cao wrote:
> >         before
> >         ------
> >         total           1026
> >         avail           1024
> >         used            2
> >         reserved        0
> >         min             1024
> >
> >         after
> >         ------
> >         total           1026
> >         avail           1024
> >         used            2
> >         max             2048
> >         reserved        0
> >         min             1024
> >
> > Signed-off-by: Yanhu Cao <gmayyyha@...il.com>
> > ---
> >  fs/ceph/caps.c    | 6 ++++--
> >  fs/ceph/debugfs.c | 7 ++++---
> >  fs/ceph/super.h   | 2 +-
> >  3 files changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> > index 5f3aa4d607de..e2c759a2ef35 100644
> > --- a/fs/ceph/caps.c
> > +++ b/fs/ceph/caps.c
> > @@ -404,8 +404,8 @@ void ceph_put_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap)
> >  }
> >
> >  void ceph_reservation_status(struct ceph_fs_client *fsc,
> > -                          int *total, int *avail, int *used, int *reserved,
> > -                          int *min)
> > +                          int *total, int *avail, int *used, int *max,
> > +                          int *reserved, int *min)
> >  {
> >       struct ceph_mds_client *mdsc = fsc->mdsc;
> >
> > @@ -417,6 +417,8 @@ void ceph_reservation_status(struct ceph_fs_client *fsc,
> >               *avail = mdsc->caps_avail_count;
> >       if (used)
> >               *used = mdsc->caps_use_count;
> > +     if (max)
> > +             *max = mdsc->caps_use_max;
>
> Can you lay out what value this will provide? I'm not convinced that
> this information is really that helpful:
>
> mdsc->caps_use_max is just set to the value of the "caps_max" mount
> option, and that information is displayed in /proc/mounts if it's not
> set to the default.
>
> What might be more interesting is to track the most recent "max_caps"
> value sent by the MDS (see the CEPH_SESSION_RECALL_STATE message
> handling). Tracking that would give us a more dynamic view of the
> current maximum requested by the MDS, which is often going to be less
> than what "caps_max" was set to at mount time.

Do you mean the 'mds_recall_max_caps'? which can be set by the MDS.
Clients use this value every time to trim caps.

There is an option mds_max_caps_per_client which is a soft limit,
which is determined by the behavior of the client.
and we recently encounter a warning '1 MDSs report oversized
cache'(ceph-v12.2.12: mds_cache_memory_limit=64G, used=100G),
Therefore, the effect is not good.

So we want to know whether the caps held by the client exceed caps_max
through the debugfs caps file (default or mount option).


>
> >       if (reserved)
> >               *reserved = mdsc->caps_reserve_count;
> >       if (min)
> > diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
> > index 481ac97b4d25..942004376588 100644
> > --- a/fs/ceph/debugfs.c
> > +++ b/fs/ceph/debugfs.c
> > @@ -138,16 +138,17 @@ static int caps_show(struct seq_file *s, void *p)
> >  {
> >       struct ceph_fs_client *fsc = s->private;
> >       struct ceph_mds_client *mdsc = fsc->mdsc;
> > -     int total, avail, used, reserved, min, i;
> > +     int total, avail, used, max, reserved, min, i;
> >       struct cap_wait *cw;
> >
> > -     ceph_reservation_status(fsc, &total, &avail, &used, &reserved, &min);
> > +     ceph_reservation_status(fsc, &total, &avail, &used, &max,
> > +                             &reserved, &min);
> >       seq_printf(s, "total\t\t%d\n"
> >                  "avail\t\t%d\n"
> >                  "used\t\t%d\n"
> >                  "reserved\t%d\n"
> >                  "min\t\t%d\n\n",
> > -                total, avail, used, reserved, min);
> > +                total, avail, used, max, reserved, min);
> >       seq_printf(s, "ino                issued           implemented\n");
> >       seq_printf(s, "-----------------------------------------------\n");
> >
> > diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> > index 60aac3aee055..79aa42d9336c 100644
> > --- a/fs/ceph/super.h
> > +++ b/fs/ceph/super.h
> > @@ -700,7 +700,7 @@ extern void ceph_unreserve_caps(struct ceph_mds_client *mdsc,
> >                              struct ceph_cap_reservation *ctx);
> >  extern void ceph_reservation_status(struct ceph_fs_client *client,
> >                                   int *total, int *avail, int *used,
> > -                                 int *reserved, int *min);
> > +                                 int *max, int *reserved, int *min);
> >
> >
> >
>
> --
> Jeff Layton <jlayton@...nel.org>
>