Add malloc_conf_2_conf_harder

This comes in handy when you're just a user of a canary system who wants to
change settings set by the configuration system itself.

test/unit/malloc_conf_2.c

@@ -0,0 +1,29 @@
+#include "test/jemalloc_test.h"
+
+const char *malloc_conf = "dirty_decay_ms:1000";
+const char *malloc_conf_2_conf_harder = "dirty_decay_ms:1234";
+
+TEST_BEGIN(test_malloc_conf_2) {
+#ifdef _WIN32
+	bool windows = true;
+#else
+	bool windows = false;
+#endif
+	/* Windows doesn't support weak symbol linker trickery. */
+	test_skip_if(windows);
+
+	ssize_t dirty_decay_ms;
+	size_t sz = sizeof(dirty_decay_ms);
+
+	int err = mallctl("opt.dirty_decay_ms", &dirty_decay_ms, &sz, NULL, 0);
+	assert_d_eq(err, 0, "Unexpected mallctl failure");
+	expect_zd_eq(dirty_decay_ms, 1234,
+	    "malloc_conf_2 setting didn't take effect");
+}
+TEST_END
+
+int
+main(void) {
+	return test(
+	    test_malloc_conf_2);
+}

test/unit/malloc_conf_2.sh

@@ -0,0 +1 @@
+export MALLOC_CONF="dirty_decay_ms:500"