osd: user specified flushing for cache tiering

This patch implements user specified cache flushing for cache tiering. In many use cases, the user traffic is high in only some fixed time, fox example, work hour. In those cases, it is desirable that the flushing job could be scheduled in the idle time, and do as much as possible, to reduce the bandwidth contention with user traffic.

The codes:
https://github.com/ceph/ceph/pull/5362

Mingxin Liu (5):
osd: parse and queue user specified flushing
osd: traverse PGs and reset agent state
osd: set the default value of agent_timer's "safe_callbacks" be false
osd: add scheduled flushing work in agent logic
osd: handle configuration changes for user specified flushing

 src/common/config_opts.h |   2 +
 src/osd/OSD.cc           | 128 ++++++++++++++++++++++++++++++++++++++++++++++-
 src/osd/OSD.h            |  12 +++--
 src/osd/PG.h             |   1 +
 src/osd/ReplicatedPG.cc  |   3 +-
 5 files changed, 141 insertions(+), 5 deletions(-)

1.9.1