DAOS-15615 test: collect memory usage after server stop (#14147)

To help understand how related memory is used.

Signed-off-by: Fan Yong <[email protected]>

src/tests/ftest/util/server_utils.py

@@ -477,7 +477,7 @@ def display_memory_info(self):
         """Display server hosts memory info."""
         self.log.debug("#" * 80)
         self.log.debug("<SERVER> Collection debug memory info")
-        run_remote(self.log, self._hosts, "free -m")
+        run_remote(self.log, self._hosts, "free -m && df -h --type=tmpfs")
         run_remote(self.log, self._hosts, "ps -eo size,pid,user,command --sort -size | head -n 6")
         self.log.debug("#" * 80)
 
@@ -720,6 +720,9 @@ def stop(self):
             # Make sure the mount directory belongs to non-root user
             self.set_scm_mount_ownership()
 
+        # Collective memory usage after stop.
+        self.display_memory_info()
+
         # Report any errors after all stop actions have been attempted
         if messages:
             raise ServerFailed("Failed to stop servers:\n  {}".format("\n  ".join(messages)))