Re: [PATCH v6 4/7] libceph: add an epoch_barrier field to struct ceph_osd_client

[Ilya Dryomov <idryomov@gmail.com>]

On Thu, Mar 30, 2017 at 8:07 PM, Jeff Layton <jlayton@redhat.com> wrote:
> Cephfs can get cap update requests that contain a new epoch barrier in
> them. When that happens we want to pause all OSD traffic until the right
> map epoch arrives.
>
> Add an epoch_barrier field to ceph_osd_client that is protected by the
> osdc->lock rwsem. When the barrier is set, and the current OSD map
> epoch is below that, pause the request target when submitting the
> request or when revisiting it. Add a way for upper layers (cephfs)
> to update the epoch_barrier as well.
>
> If we get a new map, compare the new epoch against the barrier before
> kicking requests and request another map if the map epoch is still lower
> than the one we want.
>
> If we get a map with a full pool, or at quota condition, then set the
> barrier to the current epoch value.
>
> Reviewed-by: "Yan, Zheng” <zyan@redhat.com>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  include/linux/ceph/osd_client.h |  2 ++
>  net/ceph/debugfs.c              |  3 ++-
>  net/ceph/osd_client.c           | 48 +++++++++++++++++++++++++++++++++--------
>  3 files changed, 43 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
> index 8cf644197b1a..85650b415e73 100644
> --- a/include/linux/ceph/osd_client.h
> +++ b/include/linux/ceph/osd_client.h
> @@ -267,6 +267,7 @@ struct ceph_osd_client {
>         struct rb_root         osds;          /* osds */
>         struct list_head       osd_lru;       /* idle osds */
>         spinlock_t             osd_lru_lock;
> +       u32                    epoch_barrier;
>         struct ceph_osd        homeless_osd;
>         atomic64_t             last_tid;      /* tid of last request */
>         u64                    last_linger_id;
> @@ -305,6 +306,7 @@ extern void ceph_osdc_handle_reply(struct ceph_osd_client *osdc,
>                                    struct ceph_msg *msg);
>  extern void ceph_osdc_handle_map(struct ceph_osd_client *osdc,
>                                  struct ceph_msg *msg);
> +void ceph_osdc_update_epoch_barrier(struct ceph_osd_client *osdc, u32 eb);
>
>  extern void osd_req_op_init(struct ceph_osd_request *osd_req,
>                             unsigned int which, u16 opcode, u32 flags);
> diff --git a/net/ceph/debugfs.c b/net/ceph/debugfs.c
> index d7e63a4f5578..71ba13927b3d 100644
> --- a/net/ceph/debugfs.c
> +++ b/net/ceph/debugfs.c
> @@ -62,7 +62,8 @@ static int osdmap_show(struct seq_file *s, void *p)
>                 return 0;
>
>         down_read(&osdc->lock);
> -       seq_printf(s, "epoch %d flags 0x%x\n", map->epoch, map->flags);
> +       seq_printf(s, "epoch %u barrier %u flags 0x%x\n", map->epoch,
> +                       osdc->epoch_barrier, map->flags);
>
>         for (n = rb_first(&map->pg_pools); n; n = rb_next(n)) {
>                 struct ceph_pg_pool_info *pi =
> diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> index 4e56cd1ec265..3a94e8a1c7ff 100644
> --- a/net/ceph/osd_client.c
> +++ b/net/ceph/osd_client.c
> @@ -1298,8 +1298,9 @@ static bool target_should_be_paused(struct ceph_osd_client *osdc,
>                        __pool_full(pi);
>
>         WARN_ON(pi->id != t->base_oloc.pool);
> -       return (t->flags & CEPH_OSD_FLAG_READ && pauserd) ||
> -              (t->flags & CEPH_OSD_FLAG_WRITE && pausewr);
> +       return ((t->flags & CEPH_OSD_FLAG_READ) && pauserd) ||
> +              ((t->flags & CEPH_OSD_FLAG_WRITE) && pausewr) ||
> +              (osdc->osdmap->epoch < osdc->epoch_barrier);
>  }
>
>  enum calc_target_result {
> @@ -1609,13 +1610,15 @@ static void send_request(struct ceph_osd_request *req)
>  static void maybe_request_map(struct ceph_osd_client *osdc)
>  {
>         bool continuous = false;
> +       u32 epoch = osdc->osdmap->epoch;
>
>         verify_osdc_locked(osdc);
> -       WARN_ON(!osdc->osdmap->epoch);
> +       WARN_ON_ONCE(epoch == 0);
>
>         if (ceph_osdmap_flag(osdc, CEPH_OSDMAP_FULL) ||
>             ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSERD) ||
> -           ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSEWR)) {
> +           ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSEWR) ||
> +           epoch < osdc->epoch_barrier) {
>                 dout("%s osdc %p continuous\n", __func__, osdc);
>                 continuous = true;
>         } else {

Looks like this hunk is smaller now, but I thought we agreed to drop it
entirely?  "epoch < osdc->epoch_barrier" isn't there in Objecter.

> @@ -1653,8 +1656,13 @@ static void __submit_request(struct ceph_osd_request *req, bool wrlocked)
>                 goto promote;
>         }
>
> -       if ((req->r_flags & CEPH_OSD_FLAG_WRITE) &&
> -           ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSEWR)) {
> +       if (osdc->osdmap->epoch < osdc->epoch_barrier) {
> +               dout("req %p epoch %u barrier %u\n", req, osdc->osdmap->epoch,
> +                    osdc->epoch_barrier);
> +               req->r_t.paused = true;
> +               maybe_request_map(osdc);
> +       } else if ((req->r_flags & CEPH_OSD_FLAG_WRITE) &&
> +                  ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSEWR)) {
>                 dout("req %p pausewr\n", req);
>                 req->r_t.paused = true;
>                 maybe_request_map(osdc);
> @@ -1808,7 +1816,8 @@ static void abort_request(struct ceph_osd_request *req, int err)
>
>  /*
>   * Drop all pending requests that are stalled waiting on a full condition to
> - * clear, and complete them with ENOSPC as the return code.
> + * clear, and complete them with ENOSPC as the return code. Set the
> + * osdc->epoch_barrier to the latest replay version epoch that was aborted.

This comment needs an update -- replay version is gone...

>   */
>  static void ceph_osdc_abort_on_full(struct ceph_osd_client *osdc)
>  {
> @@ -1836,8 +1845,10 @@ static void ceph_osdc_abort_on_full(struct ceph_osd_client *osdc)
>                                 abort_request(req, -ENOSPC);
>                 }
>         }
> +       /* Update the epoch barrier to current epoch */
> +       osdc->epoch_barrier = osdc->osdmap->epoch;

How important is it to update the epoch barrier only if something was
aborted?  Being here doesn't mean that something was actually aborted.

>  out:
> -       dout("return abort_on_full\n");
> +       dout("return abort_on_full barrier=%u\n", osdc->epoch_barrier);
>  }
>
>  static void check_pool_dne(struct ceph_osd_request *req)
> @@ -3293,7 +3304,8 @@ void ceph_osdc_handle_map(struct ceph_osd_client *osdc, struct ceph_msg *msg)
>         pausewr = ceph_osdmap_flag(osdc, CEPH_OSDMAP_PAUSEWR) ||
>                   ceph_osdmap_flag(osdc, CEPH_OSDMAP_FULL) ||
>                   have_pool_full(osdc);
> -       if (was_pauserd || was_pausewr || pauserd || pausewr)
> +       if (was_pauserd || was_pausewr || pauserd || pausewr ||
> +           osdc->osdmap->epoch < osdc->epoch_barrier)
>                 maybe_request_map(osdc);
>
>         kick_requests(osdc, &need_resend, &need_resend_linger);
> @@ -3311,6 +3323,24 @@ void ceph_osdc_handle_map(struct ceph_osd_client *osdc, struct ceph_msg *msg)
>         up_write(&osdc->lock);
>  }
>
> +void ceph_osdc_update_epoch_barrier(struct ceph_osd_client *osdc, u32 eb)
> +{
> +       down_read(&osdc->lock);
> +       if (unlikely(eb > osdc->epoch_barrier)) {
> +               up_read(&osdc->lock);
> +               down_write(&osdc->lock);
> +               if (osdc->epoch_barrier < eb) {

Nit: make it "eb > osdc->epoch_barrier" so it matches the unlikely
condition.

Thanks,

                Ilya