enable setting initial memory from env

paddle/testing/paddle_gtest_main.cc

@@ -30,8 +30,9 @@ int main(int argc, char** argv) {
   new_argv.push_back(
       strdup("--tryfromenv=fraction_of_gpu_memory_to_use,use_pinned_memory"));
 #else
-  new_argv.push_back(strdup("--tryfromenv=use_pinned_memory,use_mkldnn"));
-  new_argv.push_back(strdup("--undefok=use_mkldnn"));
+  new_argv.push_back(strdup(
+      "--tryfromenv=use_pinned_memory,use_mkldnn,initial_cpu_memory_in_mb"));
+  new_argv.push_back(strdup("--undefok=use_mkldnn,initial_cpu_memory_in_mb"));
 #endif
   int new_argc = static_cast<int>(new_argv.size());
   char** new_argv_address = new_argv.data();

python/paddle/fluid/__init__.py

@@ -117,7 +117,7 @@ def __bootstrap__():
 
     read_env_flags = [
         'use_pinned_memory', 'check_nan_inf', 'benchmark', 'warpctc_dir',
-        'eager_delete_scope', 'use_mkldnn'
+        'eager_delete_scope', 'use_mkldnn', 'initial_cpu_memory_in_mb'
     ]
     if core.is_compiled_with_cuda():
         read_env_flags += [