diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 6d1a03aaf..b050a7ee0 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -108,7 +108,7 @@ perlmutter-cache-build:
         - module list
         - mkdir -p ${PDC_BUILD_PATH}/perlmutter/cache
         - cd ${PDC_BUILD_PATH}/perlmutter/cache
-        - cmake ../../.. -DBUILD_MPI_TESTING=ON -DBUILD_SHARED_LIBS=ON -DPDC_SERVER_CACHE=ON -DBUILD_TESTING=ON -DCMAKE_INSTALL_PREFIX=$PDC_DIR -DPDC_ENABLE_MPI=ON -DMERCURY_DIR=$MERCURY_DIR -DCMAKE_C_COMPILER=cc -DMPI_RUN_CMD="srun -A ${PDC_PROJECT} --qos=debug --constraint=cpu --tasks-per-node=64" -DCMAKE_INSTALL_PREFIX=${PDC_INSTALL_PATH}/perlmutter/cache
+        - cmake ../../.. -DBUILD_MPI_TESTING=ON -DBUILD_SHARED_LIBS=ON -DPDC_SERVER_CACHE=ON -DBUILD_TESTING=ON -DPDC_SERVER_CACHE_MAX_GB=1 -DCMAKE_INSTALL_PREFIX=$PDC_DIR -DPDC_ENABLE_MPI=ON -DMERCURY_DIR=$MERCURY_DIR -DCMAKE_C_COMPILER=cc -DMPI_RUN_CMD="srun -A ${PDC_PROJECT} --qos=debug --constraint=cpu --tasks-per-node=64" -DCMAKE_INSTALL_PREFIX=${PDC_INSTALL_PATH}/perlmutter/cache
         - make -j
         - make install
     artifacts:
diff --git a/src/server/pdc_server_region/pdc_server_region_cache.c b/src/server/pdc_server_region/pdc_server_region_cache.c
index c150076e6..c61869d27 100644
--- a/src/server/pdc_server_region/pdc_server_region_cache.c
+++ b/src/server/pdc_server_region/pdc_server_region_cache.c
@@ -967,8 +967,9 @@ PDC_region_cache_clock_cycle(void *ptr)
                     }
                 }
                 else {
+                    pthread_mutex_lock(&pdc_obj_cache_list_mutex);
                     obj_cache_iter = obj_cache_iter->next;
-                    /* pthread_mutex_unlock(&pdc_obj_cache_list_mutex); */
+                    pthread_mutex_unlock(&pdc_obj_cache_list_mutex);
 
                     /* PDC_get_time_str(cur_time); */
                     /* fprintf(stderr, "%s ==PDC_SERVER[%d]: stop flush to allow processing new RPCs\n", */
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index db4194d2e..212916ea0 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -494,6 +494,7 @@ if(BUILD_MPI_TESTING)
     add_test(NAME obj_put_data_mpi   WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY} COMMAND mpi_test.sh ./obj_put_data ${MPI_RUN_CMD} 4 6 )
     add_test(NAME obj_get_data_mpi   WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY} COMMAND mpi_test.sh ./obj_get_data ${MPI_RUN_CMD} 4 6 )
     add_test(NAME vpicio_bdcats_mpi WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY} COMMAND run_multiple_mpi_test.sh ${MPI_RUN_CMD} 4 6 ./vpicio ./bdcats)
+    add_test(NAME vpicio_mpi_small_cache WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY} COMMAND mpi_test.sh ./vpicio ${MPI_RUN_CMD} 1 16)
 
     set_tests_properties(read_obj_shared_int                  PROPERTIES LABELS "parallel;parallel_obj" )
     set_tests_properties(read_obj_shared_float                PROPERTIES LABELS "parallel;parallel_obj" )
@@ -522,6 +523,7 @@ if(BUILD_MPI_TESTING)
 #   set_tests_properties(region_transfer_3D_skewed_mpi        PROPERTIES LABELS "parallel;parallel_region_transfer" )
     set_tests_properties(region_transfer_write_read_mpi       PROPERTIES LABELS "parallel;parallel_region_transfer" )
     set_tests_properties(vpicio_bdcats_mpi                    PROPERTIES LABELS "parallel;parallel_region_transfer" )
+    set_tests_properties(vpicio_mpi_small_cache               PROPERTIES LABELS "parallel;parallel_region_transfer" )
     set_tests_properties(region_transfer_all_mpi              PROPERTIES LABELS "parallel;parallel_region_transfer_all" )
     set_tests_properties(region_transfer_all_2D_mpi           PROPERTIES LABELS "parallel;parallel_region_transfer_all" )
     set_tests_properties(region_transfer_all_3D_mpi           PROPERTIES LABELS "parallel;parallel_region_transfer_all" )