--- libmalloc/libmalloc-317.40.8/tests/memory_pressure.c
+++ libmalloc/libmalloc-646.40.3/tests/memory_pressure.c
@@ -23,6 +23,7 @@
 	for (int t=0; t<100; t++) {
 		for (int i=0; i<cnt; i++) {
 			struct entry *p = calloc(1, sz);
+			T_QUIET; T_ASSERT_NOTNULL(p, "Failed to make allocation with size %zu", sz);
 			TAILQ_INSERT_TAIL(&head, p, next);
 		}
 		int i=0;
@@ -35,10 +36,95 @@
 	}
 }
 
+T_DECL(tiny_mem_pressure, "tiny memory pressure",
+#if TARGET_OS_WATCH
+		T_META_TIMEOUT(TEST_TIMEOUT),
+#endif // TARGET_OS_WATCH
+		T_META_ENVVAR("MallocDebugReport=stderr"),
+		T_META_ENVVAR("MallocScribble=1"),
+		T_META_ENVVAR("MallocSpaceEfficient=1"),
+		T_META_ENVVAR("MallocMaxMagazines=1"),
+		T_META_TAG_VM_NOT_PREFERRED,
+		T_META_CHECK_LEAKS(false))
+{
+	dispatch_queue_t q = dispatch_queue_create("pressure queue", 0); // serial
+	dispatch_async(q, ^{
+		while (1) {
+			malloc_zone_pressure_relief(0, 0);
+			usleep(100000);
+		}
+	});
+	stress(128, 50000);
+	T_PASS("didn't crash");
+}
+
+T_DECL(small_mem_pressure, "small memory pressure thread",
+		T_META_TAG_VM_NOT_PREFERRED,
+		T_META_RUN_CONCURRENTLY(true),
+#if TARGET_OS_WATCH
+		T_META_TIMEOUT(TEST_TIMEOUT),
+#endif // TARGET_OS_WATCH
+#if TARGET_OS_OSX
+		T_META_ALL_VALID_ARCHS(true), // test Rosetta
+		// darwintest multi-arch support relies on the first line of stderr
+		// being reserved for arch(1) complaining about a given slice being
+		// unsupported, so we can only put the malloc debug reporting on stderr
+		// when we don't need that
+		T_META_ENVVAR("MallocDebugReport=none"),
+#else // TARGET_OS_OSX
+		T_META_ENVVAR("MallocDebugReport=stderr"),
+#endif // TARGET_OS_OSX
+		T_META_ENVVAR("MallocScribble=1"),
+		T_META_ENVVAR("MallocSpaceEfficient=1"),
+		T_META_ENVVAR("MallocMaxMagazines=1"),
+		T_META_CHECK_LEAKS(false))
+{
+	dispatch_queue_t q = dispatch_queue_create("pressure queue", 0); // serial
+	dispatch_async(q, ^{
+		while (1) {
+			malloc_zone_pressure_relief(0, 0);
+			usleep(10000);
+		}
+	});
+	stress(512, 20000);
+	T_PASS("didn't crash");
+}
+
+// Disabled until rdar://83904507 is fixed
+//
+// Need to compile the test out entirely because T_META_MAYFAIL doesn't handle
+// test crashes - rdar://86164532
+#if 0
+
+T_DECL(medium_mem_pressure, "medium memory pressure thread",
+#if TARGET_OS_WATCH
+		T_META_TIMEOUT(TEST_TIMEOUT),
+#endif // TARGET_OS_WATCH
+		T_META_ENVVAR("MallocDebugReport=stderr"),
+		T_META_ENVVAR("MallocScribble=1"),
+		T_META_ENVVAR("MallocSpaceEfficient=1"),
+		T_META_ENVVAR("MallocMaxMagazines=1"),
+		T_META_MAYFAIL("Disabled until rdar://83904507 is fixed"),
+		T_META_CHECK_LEAKS(false))
+{
+	dispatch_queue_t q = dispatch_queue_create("pressure queue", 0); // serial
+	dispatch_async(q, ^{
+		while (1) {
+			malloc_zone_pressure_relief(0, 0);
+			usleep(100000);
+		}
+	});
+	stress(64*1024, 1000);
+	T_PASS("didn't crash");
+}
+
+#endif
+
 T_DECL(tiny_mem_pressure_multi, "test memory pressure in tiny on threads",
 #if TARGET_OS_WATCH
 		T_META_TIMEOUT(TEST_TIMEOUT),
 #endif // TARGET_OS_WATCH
+		T_META_TAG_VM_NOT_PREFERRED,
 		T_META_CHECK_LEAKS(false)) {
 	dispatch_group_t g = dispatch_group_create();
 	for (int i=0; i<16; i++) {
@@ -60,6 +146,8 @@
 }
 
 T_DECL(small_mem_pressure_multi, "test memory pressure in small on threads",
+		T_META_TAG_VM_NOT_PREFERRED,
+		T_META_RUN_CONCURRENTLY(true),
 #if TARGET_OS_WATCH
 		T_META_TIMEOUT(TEST_TIMEOUT),
 #endif // TARGET_OS_WATCH
@@ -87,7 +175,9 @@
 #if TARGET_OS_WATCH
 		T_META_TIMEOUT(TEST_TIMEOUT),
 #endif // TARGET_OS_WATCH
-		T_META_CHECK_LEAKS(false)) {
+		T_META_CHECK_LEAKS(false),
+	    T_META_TAG_VM_NOT_PREFERRED,
+	    T_META_RUN_CONCURRENTLY(true)) {
 	dispatch_group_t g = dispatch_group_create();
 	for (int i=0; i<30; i++) {
 		dispatch_group_async(g, dispatch_get_global_queue(0, 0), ^{