diff --git a/tools/crimson/crimson_bench_tool.py b/tools/crimson/crimson_bench_tool.py
index b3628153..7915691e 100755
--- a/tools/crimson/crimson_bench_tool.py
+++ b/tools/crimson/crimson_bench_tool.py
@@ -1249,8 +1249,8 @@ def general_pre_processing(self, tester_id):
                 self.additional_result['alien_thread_cpu_cores'] = crimson_alien_thread_cpu_cores
             elif backend == "memstore":
                 osd_core_num = self.osd_core_num
-                command += " -o 'memstore_device_bytes = 8G'"
-                self.additional_result['memstore_device_bytes'] = '8G'
+                command += f" -o 'memstore_device_bytes = {self.args.memstore_device_bytes}'"
+                self.additional_result['memstore_device_bytes'] = self.args.memstore_device_bytes
             elif backend == "seastore":
                 osd_core_num = self.osd_core_num
                 command += " -o 'seastore_cache_lru_size = 512M'"
@@ -1269,6 +1269,10 @@ def general_pre_processing(self, tester_id):
             command += f" --crimson-smp {int(osd_core_num / self.args.osd)}"
         else:
             # classic
+            if backend == "memstore":
+                osd_core_num = self.osd_core_num
+                command += f" -o 'memstore_device_bytes = {self.args.memstore_device_bytes}'"
+                self.additional_result['memstore_device_bytes'] = self.args.memstore_device_bytes
             if self.osd_core_num % self.args.osd != 0:
                 raise Exception("osd cores should be an integer multiple of osd")
             # classic osd cores bounding will be setting after ceph start
@@ -1379,7 +1383,7 @@ def general_pre_processing(self, tester_id):
         # config multicore for classic
         # all classic osds will use cpu range 0-(osd_cores*osd-1)
         # crimson multicore settings has already been set in vstart osd_cores param.
-        if not self.args.crimson:
+        if not self.args.crimson or (self.args.crimson and backend == "memstore"):
             core_per_osd = int(self.osd_core_num / self.args.osd)
             core_range_begin = 0
             core_range_end = core_per_osd
@@ -1944,6 +1948,10 @@ def not_exist(tgt):
                         type=int,
                         default=None,
                         help='set ms_async_op_threads.')
+    parser.add_argument('--memstore-device-bytes',
+                        type=str
+                        default='8G'
+                        help='set memstore_device_bytes for memstore')
     parser.add_argument('--ceph-config', '--config',
                         type=str,
                         default=None,