crimson/os/seastore/cache: add comment about backref_extent_entry_t

Signed-off-by: Xuehan Xu <xxhdx1985126@gmail.com>
(cherry picked from commit 62974a65897edce2afdb16ba99baea0193a0d4a6)

diff --git a/src/crimson/os/seastore/cache.h b/src/crimson/os/seastore/cache.h
index 3abb7bb9360c1df3ad1ec352bc52660b83254e2b..9289dda0881b579a35fffd9c5f0a10aba3591a4f 100644 (file)
--- a/src/crimson/os/seastore/cache.h
+++ b/src/crimson/os/seastore/cache.h
@@ -1106,6 +1106,14 @@ public:
   /// Dump live extents
   void dump_contents();
 
+  /**
+   * backref_extent_entry_t
+   *
+   * All the backref extent entries have to be indexed by paddr in memory,
+   * so they can be retrived by range during cleaning.
+   *
+   * See BtreeBackrefManager::retrieve_backref_extents_in_range()
+   */
   struct backref_extent_entry_t {
     backref_extent_entry_t(
       paddr_t paddr,