Add jemalloc purge (#239)

src/memory/memory_control.cpp

@@ -0,0 +1,22 @@
+#include "memory_control.hpp"
+
+#if USE_JEMALLOC
+#include <jemalloc/jemalloc.h>
+#endif
+
+namespace memory {
+
+// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
+#define STRINGIFY_HELPER(x) #x
+// NOLINTNEXTLINE(cppcoreguidelines-macro-usage)
+#define STRINGIFY(x) STRINGIFY_HELPER(x)
+
+void PurgeUnusedMemory() {
+#if USE_JEMALLOC
+  mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".purge", nullptr, nullptr, nullptr, 0);
+#endif
+}
+
+#undef STRINGIFY
+#undef STRINGIFY_HELPER
+}  // namespace memory