osd/OSD: Add pg_num_history comment

Signed-off-by: Matan Breizman <mbreizma@redhat.com>

diff --git a/src/osd/OSD.h b/src/osd/OSD.h
index e5f3510e2a5239b14d5e6e5031f963b74def7901..1ad1b509fc1c746bd8079145b593355169aafe07 100644 (file)
--- a/src/osd/OSD.h
+++ b/src/osd/OSD.h
@@ -1666,6 +1666,12 @@ protected:
     return osdmap ? osdmap->get_epoch() : 0;
   }
 
+  /* When handling OSDMaps pg_num_history is used to
+   * track any changes to number of PGs of each pool
+   * to be used later in order to identify PG splits and merges.
+   * See: OSD::track_pools_and_pg_num_changes
+   *      and OSDService::identify_splits_and_merges.
+   */
   pool_pg_num_history_t pg_num_history;
 
   ceph::shared_mutex map_lock = ceph::make_shared_mutex("OSD::map_lock");