Merge PR #21719 into master

* refs/pull/21719/head:
	mds: trim log during shutdown to clean metadata

Reviewed-by: Zheng Yan <zyan@redhat.com>

diff --cc src/mds/MDCache.cc
index c947be26e3565f9ff9d22cbb19dd0cf57844f498,62a4b8f7ce5ab51d1064ffcad21044ac319b76ca..eb07de00ed1aa27f044df43045401345c163f148
--- 1/src/mds/MDCache.cc
--- 2/src/mds/MDCache.cc
+++ b/src/mds/MDCache.cc
@@@ -7706,10 -7676,11 +7706,10 @@@ bool MDCache::shutdown_pass(
    trim(UINT64_MAX);
    dout(5) << "lru size now " << lru.lru_get_size() << "/" << bottom_lru.lru_get_size() << dendl;
  
-   // SUBTREES
+   // Export all subtrees to another active (usually rank 0) if not rank 0
    int num_auth_subtree = 0;
    if (!subtrees.empty() &&
 -      mds->get_nodeid() != 0 && 
 -      migrator->get_export_queue_size() == 0) {
 +      mds->get_nodeid() != 0) {
      dout(7) << "looking for subtrees to export to mds0" << dendl;
      list<CDir*> ls;
      for (map<CDir*, set<CDir*> >::iterator it = subtrees.begin();