--- /dev/null
+++ libmalloc/libmalloc-425.100.7/tests/memory_pressure.c
@@ -0,0 +1,189 @@
+#include <darwintest.h>
+#include <dispatch/dispatch.h>
+#include <malloc/malloc.h>
+#include <os/lock.h>
+#include <stdlib.h>
+#include <sys/queue.h>
+
+#if TARGET_OS_WATCH
+#define TEST_TIMEOUT 1200
+#endif // TARGET_OS_WATCH
+
+TAILQ_HEAD(thead, entry);
+struct entry {
+	TAILQ_ENTRY(entry) next;
+};
+
+static void
+stress(size_t sz, size_t cnt)
+{
+	struct thead head = TAILQ_HEAD_INITIALIZER(head);
+	TAILQ_INIT(&head);
+
+	for (int t=0; t<100; t++) {
+		for (int i=0; i<cnt; i++) {
+			struct entry *p = calloc(1, sz);
+			TAILQ_INSERT_TAIL(&head, p, next);
+		}
+		int i=0;
+		struct entry *p;
+		while ((p = TAILQ_FIRST(&head)) != NULL) {
+			TAILQ_REMOVE(&head, p, next);
+			free((void *)p);
+			i++;
+		}
+	}
+}
+
+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_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",
+#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_CHECK_LEAKS(false)) {
+	dispatch_group_t g = dispatch_group_create();
+	for (int i=0; i<16; i++) {
+		dispatch_group_async(g, dispatch_get_global_queue(0, 0), ^{
+			stress(128, 100000);
+		});
+	}
+	dispatch_group_notify(g, dispatch_get_global_queue(0, 0), ^{
+		T_PASS("didn't crash!");
+		T_END;
+	});
+	dispatch_release(g);
+
+	while (1) {
+		T_LOG("malloc_zone_pressure_relief");
+		malloc_zone_pressure_relief(malloc_default_zone(), 0);
+		sleep(1);
+	}
+}
+
+T_DECL(small_mem_pressure_multi, "test memory pressure in small on threads",
+#if TARGET_OS_WATCH
+		T_META_TIMEOUT(TEST_TIMEOUT),
+#endif // TARGET_OS_WATCH
+		T_META_CHECK_LEAKS(false)) {
+	dispatch_group_t g = dispatch_group_create();
+	for (int i=0; i<3; i++) {
+		dispatch_group_async(g, dispatch_get_global_queue(0, 0), ^{
+			stress(1024, 100000);
+		});
+	}
+	dispatch_group_notify(g, dispatch_get_global_queue(0, 0), ^{
+		T_PASS("didn't crash!");
+		T_END;
+	});
+	dispatch_release(g);
+
+	while (1) {
+		T_LOG("malloc_zone_pressure_relief");
+		malloc_zone_pressure_relief(malloc_default_zone(), 0);
+		sleep(1);
+	}
+}
+
+T_DECL(medium_mem_pressure_multi, "test memory pressure in medium on threads",
+#if TARGET_OS_WATCH
+		T_META_TIMEOUT(TEST_TIMEOUT),
+#endif // TARGET_OS_WATCH
+		T_META_CHECK_LEAKS(false)) {
+	dispatch_group_t g = dispatch_group_create();
+	for (int i=0; i<30; i++) {
+		dispatch_group_async(g, dispatch_get_global_queue(0, 0), ^{
+			stress(64*1024, 1000);
+		});
+	}
+	dispatch_group_notify(g, dispatch_get_global_queue(0, 0), ^{
+		T_PASS("didn't crash!");
+		T_END;
+	});
+	dispatch_release(g);
+
+	while (1) {
+		T_LOG("malloc_zone_pressure_relief");
+		malloc_zone_pressure_relief(malloc_default_zone(), 0);
+		sleep(1);
+	}
+}