[PATCH v2 0/4] flush the mdlog before waiting on unsafe reqs

[xiubli@redhat.com]

From: Xiubo Li <xiubli@redhat.com>

For the client requests who will have unsafe and safe replies from
MDS daemons, in the MDS side the MDS daemons won't flush the mdlog
(journal log) immediatelly, because they think it's unnecessary.
That's true for most cases but not all, likes the fsync request.
The fsync will wait until all the unsafe replied requests to be
safely replied.

Normally if there have multiple threads or clients are running, the
whole mdlog in MDS daemons could be flushed in time if any request
will trigger the mdlog submit thread. So usually we won't experience
the normal operations will stuck for a long time. But in case there
has only one client with only thread is running, the stuck phenomenon
maybe obvious and the worst case it must wait at most 5 seconds to
wait the mdlog to be flushed by the MDS's tick thread periodically.

This patch will trigger to flush the mdlog in all the relevant and
auth MDSes manually just before waiting the unsafe requests to finish.


Changed in V2:
- send mdlog flush request to unsafe req relevant and auth MDSes only
instead of all of them.
- rename the first two commits' subject.
- fix the log messages.
- remove the feature bits fixing patch.
- fix some comments.
- remove flush_mdlog() wrapper.
- update the ceph_session_op_name() for new _REQUEST_FLUSH_MDLOG.



Xiubo Li (4):
  ceph: make ceph_create_session_msg a global symbol
  ceph: make iterate_sessions a global symbol
  ceph: flush mdlog before umounting
  ceph: flush the mdlog before waiting on unsafe reqs

 fs/ceph/caps.c               | 104 ++++++++++++++++++++++++++---------
 fs/ceph/mds_client.c         |  90 ++++++++++++++++++++++--------
 fs/ceph/mds_client.h         |   5 ++
 fs/ceph/strings.c            |   1 +
 include/linux/ceph/ceph_fs.h |   1 +
 5 files changed, 152 insertions(+), 49 deletions(-)

-- 
2.27.0