fixing sizeof for StringHashTable

pandas/_libs/hashtable_class_helper.pxi.in

@@ -671,10 +671,11 @@ cdef class StringHashTable(HashTable):
             self.table = NULL
 
     def sizeof(self, deep=False):
-        """ return the size of my table in bytes """
-        return self.table.n_buckets * (sizeof(char *) + # keys
-                                       sizeof(Py_ssize_t) + # vals
-                                       sizeof(uint32_t)) # flags
+        overhead = 4 * sizeof(uint32_t) + 3 * sizeof(uint32_t*)
+        for_flags = max(1, self.table.n_buckets >> 5) * sizeof(uint32_t)
+        for_pairs =  self.table.n_buckets * (sizeof(char *) +      # keys
+                                             sizeof(Py_ssize_t))   # vals
+        return overhead + for_flags + for_pairs
 
     cpdef get_item(self, str val):
         cdef:

pandas/tests/libs/test_hashtable.py

@@ -140,6 +140,19 @@ def test_tracemalloc_works(self, table_type, dtype):
             assert get_allocated_khash_memory() == 0
 
 
+def test_tracemalloc_works_for_StringHashTable():
+    N = 1000
+    keys = np.arange(N).astype(np.unicode).astype(np.object)
+    with activated_tracemalloc():
+        table = ht.StringHashTable()
+        table.map_locations(keys)
+        used = get_allocated_khash_memory()
+        my_size = table.sizeof()
+        assert used == my_size
+        del table
+        assert get_allocated_khash_memory() == 0
+
+
 @pytest.mark.parametrize(
     "table_type, dtype",
     [