osd: document split tracking structures a bit

Signed-off-by: Sage Weil <sage@redhat.com>

diff --git a/src/osd/OSD.h b/src/osd/OSD.h
index 2d10d6f3b032d6445f5c0489842203d5d6a9ec27..e4517873e89bbd3667c2a2d8fa7d328a4022b7be 100644 (file)
--- a/src/osd/OSD.h
+++ b/src/osd/OSD.h
@@ -913,8 +913,13 @@ public:
 private:
   // split
   Mutex in_progress_split_lock;
+  // splits are "pending" after OSD has consumed the map indicating the PG should
+  // split but the PG has not yet processed the map.
   map<spg_t, spg_t> pending_splits; // child -> parent
   map<spg_t, set<spg_t> > rev_pending_splits; // parent -> [children]
+
+  // splits are "in progress" after the PG has gotten the map, and we hold the
+  // parent lock, but the children have not yet been created.
   set<spg_t> in_progress_splits;       // child
 
 public: