osd/PG: Add helper method to get the average size of objects in a PG.

Factor out the code in PG::queue_recovery() that determines the average
object size in a PG to PG::get_average_object_size(). This is used to
determine the cost of a background operation for e.g., recovery,
snaptrim in case mClock scheduler is employed.

Signed-off-by: Sridhar Seshasayee <[email protected]>

Author: sseshasa

src/osd/PG.cc

@@ -420,15 +420,7 @@ void PG::queue_recovery()
     dout(10) << "queue_recovery -- queuing" << dendl;
     recovery_queued = true;
     // Let cost per object be the average object size
-    auto num_bytes = static_cast<uint64_t>(
-      std::max<int64_t>(
-	0, // ensure bytes is non-negative
-	info.stats.stats.sum.num_bytes));
-    auto num_objects = static_cast<uint64_t>(
-      std::max<int64_t>(
-	1, // ensure objects is non-negative and non-zero
-	info.stats.stats.sum.num_objects));
-    uint64_t cost_per_object = std::max<uint64_t>(num_bytes / num_objects, 1);
+    uint64_t cost_per_object = get_average_object_size();
     osd->queue_for_recovery(
       this, cost_per_object, recovery_state.get_recovery_op_priority()
     );

src/osd/PG.h

@@ -1024,6 +1024,19 @@ class PG : public DoutPrefixProvider,
     return num_bytes;
   }
 
+  uint64_t get_average_object_size() {
+    ceph_assert(ceph_mutex_is_locked_by_me(_lock));
+    auto num_bytes = static_cast<uint64_t>(
+      std::max<int64_t>(
+        0, // ensure bytes is non-negative
+        info.stats.stats.sum.num_bytes));
+    auto num_objects = static_cast<uint64_t>(
+      std::max<int64_t>(
+        1, // ensure objects is non-negative and non-zero
+        info.stats.stats.sum.num_objects));
+    return std::max<uint64_t>(num_bytes / num_objects, 1);
+  }
+
 protected:
 
   /*