partition: add method to calculate memory size of a partition

Once that is added, also add a method to a memtable entry to calculate
the entire size of a memtable entry. Right now we only have one method
to calculate the size minus rows.

Signed-off-by: Glauber Costa <glauber@scylladb.com>

memtable.hh

@@ -70,6 +70,14 @@ public:
         return allocator.object_memory_size_in_allocator(this) + external_memory_usage_without_rows();
     }
 
+    size_t size_in_allocator(allocation_strategy& allocator) {
+        auto size = size_in_allocator_without_rows(allocator);
+        for (auto&& v : _pe.versions()) {
+            size += v.size_in_allocator(allocator);
+        }
+        return size;
+    }
+
     struct compare {
         dht::decorated_key::less_comparator _c;
 

partition_version.cc

@@ -63,6 +63,11 @@ partition_version::~partition_version()
     }
 }
 
+size_t partition_version::size_in_allocator(allocation_strategy& allocator) const {
+    return allocator.object_memory_size_in_allocator(this) +
+           partition().external_memory_usage();
+}
+
 namespace {
 
 GCC6_CONCEPT(

partition_version.hh

@@ -130,6 +130,8 @@ public:
 
     bool is_referenced() const { return _backref; }
     partition_version_ref& back_reference() { return *_backref; }
+
+    size_t size_in_allocator(allocation_strategy& allocator) const;
 };
 
 using partition_version_range = anchorless_list_base_hook<partition_version>::range;