Re: [PATCH] ceph: enable async dirops by default

[Ilya Dryomov <idryomov@gmail.com>]

On Wed, Sep 1, 2021 at 6:54 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> On Mon, 2021-08-09 at 12:44 -0400, Jeff Layton wrote:
> > Async dirops have been supported in mainline kernels for quite some time
> > now, and we've recently (as of June) started doing regular testing in
> > teuthology with '-o nowsync'. So far, that hasn't uncovered any issues,
> > so I think the time is right to flip the default for this option.
> >
> > Enable async dirops by default, and change /proc/mounts to show "wsync"
> > when they are disabled rather than "nowsync" when they are enabled.
> >
> > Cc: Patrick Donnelly <pdonnell@redhat.com>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/ceph/super.c | 4 ++--
> >  fs/ceph/super.h | 3 ++-
> >  2 files changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> > index 609ffc8c2d78..f517ad9eeb26 100644
> > --- a/fs/ceph/super.c
> > +++ b/fs/ceph/super.c
> > @@ -698,8 +698,8 @@ static int ceph_show_options(struct seq_file *m, struct dentry *root)
> >       if (fsopt->flags & CEPH_MOUNT_OPT_CLEANRECOVER)
> >               seq_show_option(m, "recover_session", "clean");
> >
> > -     if (fsopt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS)
> > -             seq_puts(m, ",nowsync");
> > +     if (!(fsopt->flags & CEPH_MOUNT_OPT_ASYNC_DIROPS))
> > +             seq_puts(m, ",wsync");
> >
> >       if (fsopt->wsize != CEPH_MAX_WRITE_SIZE)
> >               seq_printf(m, ",wsize=%u", fsopt->wsize);
> > diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> > index 389b45ac291b..0bc36cf4c683 100644
> > --- a/fs/ceph/super.h
> > +++ b/fs/ceph/super.h
> > @@ -48,7 +48,8 @@
> >
> >  #define CEPH_MOUNT_OPT_DEFAULT                       \
> >       (CEPH_MOUNT_OPT_DCACHE |                \
> > -      CEPH_MOUNT_OPT_NOCOPYFROM)
> > +      CEPH_MOUNT_OPT_NOCOPYFROM |            \
> > +      CEPH_MOUNT_OPT_ASYNC_DIROPS)
> >
> >  #define ceph_set_mount_opt(fsc, opt) \
> >       (fsc)->mount_options->flags |= CEPH_MOUNT_OPT_##opt
>
> I think we ought to wait to merge this into mainline just yet, but I'd
> like to leave it in the "testing" branch for now.
>
> I've been working this bug with Patrick for the last month or two:
>
>     https://tracker.ceph.com/issues/51279
>
> In at least one case, the problem seems to be that the MDS failed an
> async create with an ENOSPC error. The kclient's error handling around
> this is pretty non-existent right now, so it caused an unmount to hang.
>
> It's a pity we still don't have revoke()...
>
> I've started working on a series to clean this up, but in the meantime I
> think we ought to wait until that's in place before we make nowsync the
> default.
>
> Sound ok?

Yeah, I don't see any rush to make it the default especially given that
it hasn't been on in testing that long.

Thanks,

                Ilya