mds: trim non-auth subtree more aggressively

When a non-auth dirfrag is pinned by uncommitted slave update,
there still can be non-auth child dirfrags that are trimmable.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: don't start new segment while finishing disambiguate imports

This avoid inserting ESubtreeMap among EImportFinish events that
finish disambiguate imports. Because the ESubtreeMap reflects the
subtree state when all EImportFinish events are replayed.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: treat cluster as degraded when there is clientreplay MDS

This forbids exporting subtrees and fragmenting dirfrags when there
is MDS in clientreplay state. During replaying client requests, the
MDS may need to authpin some remote objects. Exporting subtrees and
fragmenting dirfrags slow down replaying client requests.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
mds: handle freeze authpin race

For across authority rename, the MDS first freezes the source inode's
authpin. It happens while the source dentry isn't locked. So when the
inode's authpin become frozen, the source dentry may have changed and
be linked to a different inode.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Merge pull request #1584 from ceph/wip-multimds

Wip multimds

Reviewed-by: Sage Weil <sage@inktank.com>