Re: [PATCH v5 2/6] libceph: abort already submitted but abortable requests when map or pool goes full

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-03-28 at 16:34 +0200, Ilya Dryomov wrote:
> On Sat, Feb 25, 2017 at 6:43 PM, Jeff Layton <jlayton@redhat.com> wrote:
> > When a Ceph volume hits capacity, a flag is set in the OSD map to
> > indicate that, and a new map is sprayed around the cluster. With cephfs
> > we want it to shut down any abortable requests that are in progress with
> > an -ENOSPC error as they'd just hang otherwise.
> > 
> > Add a new ceph_osdc_abort_on_full helper function to handle this. It
> > will first check whether there is an out-of-space condition in the
> > cluster. It will then walk the tree and abort any request that has
> > r_abort_on_full set with an ENOSPC error. Call this new function
> > directly whenever we get a new OSD map.
> > 
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  net/ceph/osd_client.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 42 insertions(+)
> > 
> > diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> > index 8fc0ccc7126f..b286ff6dec29 100644
> > --- a/net/ceph/osd_client.c
> > +++ b/net/ceph/osd_client.c
> > @@ -1770,6 +1770,47 @@ static void complete_request(struct ceph_osd_request *req, int err)
> >         ceph_osdc_put_request(req);
> >  }
> > 
> > +/*
> > + * Drop all pending requests that are stalled waiting on a full condition to
> > + * clear, and complete them with ENOSPC as the return code.
> > + */
> > +static void ceph_osdc_abort_on_full(struct ceph_osd_client *osdc)
> > +{
> > +       struct ceph_osd_request *req;
> > +       struct ceph_osd *osd;
> 
> These variables could have narrower scope.
> 
> > +       struct rb_node *m, *n;
> > +       u32 latest_epoch = 0;
> > +       bool osdmap_full = ceph_osdmap_flag(osdc, CEPH_OSDMAP_FULL);
> 
> This variable is redundant.
> 
> > +
> > +       dout("enter abort_on_full\n");
> > +
> > +       if (!osdmap_full && !have_pool_full(osdc))
> > +               goto out;
> > +
> > +       for (n = rb_first(&osdc->osds); n; n = rb_next(n)) {
> > +               osd = rb_entry(n, struct ceph_osd, o_node);
> > +               mutex_lock(&osd->lock);
> 
> No need to take osd->lock here as osdc->lock is held for write.
> 

Could you explain how this locking works?

It appeared to me that o_requests was protected by osd->lock based on
when link_request is called in __submit_request. If the osdc->lock is
sufficient, then why take the osd->lock before grabbing the tid and
linking it into the tree?

> > +               m = rb_first(&osd->o_requests);
> > +               while (m) {
> > +                       req = rb_entry(m, struct ceph_osd_request, r_node);
> > +                       m = rb_next(m);
> > +
> > +                       if (req->r_abort_on_full &&
> > +                           (osdmap_full || pool_full(osdc, req->r_t.base_oloc.pool))) {
> 
> Over 80 lines and I think we need target_oloc instead of base_oloc
> here.
> 
> > +                               u32 cur_epoch = le32_to_cpu(req->r_replay_version.epoch);
> 
> Is replay_version used this way in the userspace client?  It is an ack
> vs commit leftover and AFAICT it is never set (i.e. always 0'0) in newer
> Objecter, so something is wrong here.
> 
> > +
> > +                               dout("%s: abort tid=%llu flags 0x%x\n", __func__, req->r_tid, req->r_flags);
> 
> Over 80 lines and probably unnecessary -- complete_request() has
> a similar dout.
> 
> > +                               complete_request(req, -ENOSPC);
> 
> This should be abort_request() (newly introduced in 4.11).
> 

Fixed most of the above, but could you explain this bit?

abort_request() just calls cancel_map_check() and then does a
complete_request(). Why do we want to cancel the map check here?

> > +                               if (cur_epoch > latest_epoch)
> > +                                       latest_epoch = cur_epoch;
> > +                       }
> > +               }
> > +               mutex_unlock(&osd->lock);
> > +       }
> > +out:
> > +       dout("return abort_on_full latest_epoch=%u\n", latest_epoch);
> > +}
> > +
> >  static void cancel_map_check(struct ceph_osd_request *req)
> >  {
> >         struct ceph_osd_client *osdc = req->r_osdc;
> > @@ -3232,6 +3273,7 @@ void ceph_osdc_handle_map(struct ceph_osd_client *osdc, struct ceph_msg *msg)
> > 
> >         ceph_monc_got_map(&osdc->client->monc, CEPH_SUB_OSDMAP,
> >                           osdc->osdmap->epoch);
> > +       ceph_osdc_abort_on_full(osdc);
> 
> Nit: swap ceph_osdc_abort_on_full() and ceph_monc_got_map() so that
> ceph_osdc_abort_on_full() follows kick_requests().  No real reason
> other than for "I processed this map" notification to go last, after
> the map is fully processed.
> 

Sure, np.

Thanks,
-- 
Jeff Layton <jlayton@redhat.com>