diff --git a/Makefile.in b/Makefile.in
index c35bb7ed..3d99a409 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -57,6 +57,7 @@ cfgoutputs_out := @cfgoutputs_out@
 enable_autogen := @enable_autogen@
 enable_prof := @enable_prof@
 enable_zone_allocator := @enable_zone_allocator@
+enable_experimental_smallocx := @enable_experimental_smallocx@
 MALLOC_CONF := @JEMALLOC_CPREFIX@MALLOC_CONF
 link_whole_archive := @link_whole_archive@
 DSO_LDFLAGS = @DSO_LDFLAGS@
@@ -235,6 +236,10 @@ TESTS_INTEGRATION := $(srcroot)test/integration/aligned_alloc.c \
 	$(srcroot)test/integration/thread_arena.c \
 	$(srcroot)test/integration/thread_tcache_enabled.c \
 	$(srcroot)test/integration/xallocx.c
+ifeq (@enable_experimental_smallocx@, 1)
+TESTS_INTEGRATION += \
+  $(srcroot)test/integration/smallocx.c
+endif
 ifeq (@enable_cxx@, 1)
 CPP_SRCS := $(srcroot)src/jemalloc_cpp.cpp
 TESTS_INTEGRATION_CPP := $(srcroot)test/integration/cpp/basic.cpp
diff --git a/test/integration/smallocx.c b/test/integration/smallocx.c
new file mode 100644
index 00000000..376fec25
--- /dev/null
+++ b/test/integration/smallocx.c
@@ -0,0 +1,292 @@
+#include "test/jemalloc_test.h"
+
+static unsigned
+get_nsizes_impl(const char *cmd) {
+	unsigned ret;
+	size_t z;
+
+	z = sizeof(unsigned);
+	assert_d_eq(mallctl(cmd, (void *)&ret, &z, NULL, 0), 0,
+	    "Unexpected mallctl(\"%s\", ...) failure", cmd);
+
+	return ret;
+}
+
+static unsigned
+get_nlarge(void) {
+	return get_nsizes_impl("arenas.nlextents");
+}
+
+static size_t
+get_size_impl(const char *cmd, size_t ind) {
+	size_t ret;
+	size_t z;
+	size_t mib[4];
+	size_t miblen = 4;
+
+	z = sizeof(size_t);
+	assert_d_eq(mallctlnametomib(cmd, mib, &miblen),
+	    0, "Unexpected mallctlnametomib(\"%s\", ...) failure", cmd);
+	mib[2] = ind;
+	z = sizeof(size_t);
+	assert_d_eq(mallctlbymib(mib, miblen, (void *)&ret, &z, NULL, 0),
+	    0, "Unexpected mallctlbymib([\"%s\", %zu], ...) failure", cmd, ind);
+
+	return ret;
+}
+
+static size_t
+get_large_size(size_t ind) {
+	return get_size_impl("arenas.lextent.0.size", ind);
+}
+
+/*
+ * On systems which can't merge extents, tests that call this function generate
+ * a lot of dirty memory very quickly.  Purging between cycles mitigates
+ * potential OOM on e.g. 32-bit Windows.
+ */
+static void
+purge(void) {
+	assert_d_eq(mallctl("arena.0.purge", NULL, NULL, NULL, 0), 0,
+	    "Unexpected mallctl error");
+}
+
+/*
+ * GCC "-Walloc-size-larger-than" warning detects when one of the memory
+ * allocation functions is called with a size larger than the maximum size that
+ * they support. Here we want to explicitly test that the allocation functions
+ * do indeed fail properly when this is the case, which triggers the warning.
+ * Therefore we disable the warning for these tests.
+ */
+JEMALLOC_DIAGNOSTIC_PUSH
+JEMALLOC_DIAGNOSTIC_IGNORE_ALLOC_SIZE_LARGER_THAN
+
+TEST_BEGIN(test_overflow) {
+	size_t largemax;
+
+	largemax = get_large_size(get_nlarge()-1);
+
+	assert_ptr_null(smallocx(largemax+1, 0).ptr,
+	    "Expected OOM for smallocx(size=%#zx, 0)", largemax+1);
+
+	assert_ptr_null(smallocx(ZU(PTRDIFF_MAX)+1, 0).ptr,
+	    "Expected OOM for smallocx(size=%#zx, 0)", ZU(PTRDIFF_MAX)+1);
+
+	assert_ptr_null(smallocx(SIZE_T_MAX, 0).ptr,
+	    "Expected OOM for smallocx(size=%#zx, 0)", SIZE_T_MAX);
+
+	assert_ptr_null(smallocx(1, MALLOCX_ALIGN(ZU(PTRDIFF_MAX)+1)).ptr,
+	    "Expected OOM for smallocx(size=1, MALLOCX_ALIGN(%#zx))",
+	    ZU(PTRDIFF_MAX)+1);
+}
+TEST_END
+
+static void *
+remote_alloc(void *arg) {
+	unsigned arena;
+	size_t sz = sizeof(unsigned);
+	assert_d_eq(mallctl("arenas.create", (void *)&arena, &sz, NULL, 0), 0,
+	    "Unexpected mallctl() failure");
+	size_t large_sz;
+	sz = sizeof(size_t);
+	assert_d_eq(mallctl("arenas.lextent.0.size", (void *)&large_sz, &sz,
+	    NULL, 0), 0, "Unexpected mallctl failure");
+
+	smallocx_return_t r = smallocx(large_sz, MALLOCX_ARENA(arena)
+                                 | MALLOCX_TCACHE_NONE);
+	void *ptr = r.ptr;
+  assert_zu_eq(r.size, nallocx(large_sz, MALLOCX_ARENA(arena)
+                               | MALLOCX_TCACHE_NONE),
+               "Expected smalloc(size,flags).size == nallocx(size,flags)");
+	void **ret = (void **)arg;
+	*ret = ptr;
+
+	return NULL;
+}
+
+TEST_BEGIN(test_remote_free) {
+	thd_t thd;
+	void *ret;
+	thd_create(&thd, remote_alloc, (void *)&ret);
+	thd_join(thd, NULL);
+	assert_ptr_not_null(ret, "Unexpected smallocx failure");
+
+	/* Avoid TCACHE_NONE to explicitly test tcache_flush(). */
+	dallocx(ret, 0);
+	mallctl("thread.tcache.flush", NULL, NULL, NULL, 0);
+}
+TEST_END
+
+TEST_BEGIN(test_oom) {
+	size_t largemax;
+	bool oom;
+	void *ptrs[3];
+	unsigned i;
+
+	/*
+	 * It should be impossible to allocate three objects that each consume
+	 * nearly half the virtual address space.
+	 */
+	largemax = get_large_size(get_nlarge()-1);
+	oom = false;
+	for (i = 0; i < sizeof(ptrs) / sizeof(void *); i++) {
+		ptrs[i] = smallocx(largemax, 0).ptr;
+		if (ptrs[i] == NULL) {
+			oom = true;
+		}
+	}
+	assert_true(oom,
+	    "Expected OOM during series of calls to smallocx(size=%zu, 0)",
+	    largemax);
+	for (i = 0; i < sizeof(ptrs) / sizeof(void *); i++) {
+		if (ptrs[i] != NULL) {
+			dallocx(ptrs[i], 0);
+		}
+	}
+	purge();
+
+#if LG_SIZEOF_PTR == 3
+	assert_ptr_null(smallocx(0x8000000000000000ULL,
+	    MALLOCX_ALIGN(0x8000000000000000ULL)).ptr,
+	    "Expected OOM for smallocx()");
+	assert_ptr_null(smallocx(0x8000000000000000ULL,
+	    MALLOCX_ALIGN(0x80000000)).ptr,
+	    "Expected OOM for smallocx()");
+#else
+	assert_ptr_null(smallocx(0x80000000UL, MALLOCX_ALIGN(0x80000000UL)).ptr,
+	    "Expected OOM for smallocx()");
+#endif
+}
+TEST_END
+
+/* Re-enable the "-Walloc-size-larger-than=" warning */
+JEMALLOC_DIAGNOSTIC_POP
+
+TEST_BEGIN(test_basic) {
+#define MAXSZ (((size_t)1) << 23)
+	size_t sz;
+
+	for (sz = 1; sz < MAXSZ; sz = nallocx(sz, 0) + 1) {
+    smallocx_return_t ret;
+		size_t nsz, rsz, smz;
+		void *p;
+		nsz = nallocx(sz, 0);
+		assert_zu_ne(nsz, 0, "Unexpected nallocx() error");
+		ret = smallocx(sz, 0);
+    p = ret.ptr;
+    smz = ret.size;
+		assert_ptr_not_null(p,
+		    "Unexpected smallocx(size=%zx, flags=0) error", sz);
+		rsz = sallocx(p, 0);
+		assert_zu_ge(rsz, sz, "Real size smaller than expected");
+		assert_zu_eq(nsz, rsz, "nallocx()/sallocx() size mismatch");
+    assert_zu_eq(nsz, smz, "nallocx()/smallocx() size mismatch");
+		dallocx(p, 0);
+
+		ret = smallocx(sz, 0);
+    p = ret.ptr;
+    smz = ret.size;
+		assert_ptr_not_null(p,
+		    "Unexpected smallocx(size=%zx, flags=0) error", sz);
+		dallocx(p, 0);
+
+		nsz = nallocx(sz, MALLOCX_ZERO);
+		assert_zu_ne(nsz, 0, "Unexpected nallocx() error");
+    assert_zu_ne(smz, 0, "Unexpected smallocx() error");
+    ret = smallocx(sz, MALLOCX_ZERO);
+		p = ret.ptr;
+		assert_ptr_not_null(p,
+		    "Unexpected smallocx(size=%zx, flags=MALLOCX_ZERO) error",
+		    nsz);
+		rsz = sallocx(p, 0);
+		assert_zu_eq(nsz, rsz, "nallocx()/sallocx() rsize mismatch");
+    assert_zu_eq(nsz, smz, "nallocx()/smallocx() size mismatch");
+		dallocx(p, 0);
+		purge();
+	}
+#undef MAXSZ
+}
+TEST_END
+
+TEST_BEGIN(test_alignment_and_size) {
+	const char *percpu_arena;
+	size_t sz = sizeof(percpu_arena);
+
+	if(mallctl("opt.percpu_arena", (void *)&percpu_arena, &sz, NULL, 0) ||
+	    strcmp(percpu_arena, "disabled") != 0) {
+		test_skip("test_alignment_and_size skipped: "
+		    "not working with percpu arena.");
+	};
+#define MAXALIGN (((size_t)1) << 23)
+#define NITER 4
+	size_t nsz, rsz, smz, alignment, total;
+	unsigned i;
+	void *ps[NITER];
+
+	for (i = 0; i < NITER; i++) {
+		ps[i] = NULL;
+	}
+
+	for (alignment = 8;
+	    alignment <= MAXALIGN;
+	    alignment <<= 1) {
+		total = 0;
+		for (sz = 1;
+		    sz < 3 * alignment && sz < (1U << 31);
+		    sz += (alignment >> (LG_SIZEOF_PTR-1)) - 1) {
+			for (i = 0; i < NITER; i++) {
+				nsz = nallocx(sz, MALLOCX_ALIGN(alignment) |
+				    MALLOCX_ZERO);
+				assert_zu_ne(nsz, 0,
+				    "nallocx() error for alignment=%zu, "
+				    "size=%zu (%#zx)", alignment, sz, sz);
+        smallocx_return_t ret = smallocx(sz, MALLOCX_ALIGN(alignment) |
+                                         MALLOCX_ZERO);
+				ps[i] = ret.ptr;
+				assert_ptr_not_null(ps[i],
+				    "smallocx() error for alignment=%zu, "
+				    "size=%zu (%#zx)", alignment, sz, sz);
+				rsz = sallocx(ps[i], 0);
+        smz = ret.size;
+				assert_zu_ge(rsz, sz,
+				    "Real size smaller than expected for "
+				    "alignment=%zu, size=%zu", alignment, sz);
+				assert_zu_eq(nsz, rsz,
+				    "nallocx()/sallocx() size mismatch for "
+				    "alignment=%zu, size=%zu", alignment, sz);
+        assert_zu_eq(nsz, smz,
+            "nallocx()/smallocx() size mismatch for "
+            "alignment=%zu, size=%zu", alignment, sz);
+				assert_ptr_null(
+				    (void *)((uintptr_t)ps[i] & (alignment-1)),
+				    "%p inadequately aligned for"
+				    " alignment=%zu, size=%zu", ps[i],
+				    alignment, sz);
+				total += rsz;
+				if (total >= (MAXALIGN << 1)) {
+					break;
+				}
+			}
+			for (i = 0; i < NITER; i++) {
+				if (ps[i] != NULL) {
+					dallocx(ps[i], 0);
+					ps[i] = NULL;
+				}
+			}
+		}
+		purge();
+	}
+#undef MAXALIGN
+#undef NITER
+}
+TEST_END
+
+int
+main(void) {
+	return test(
+	    test_overflow,
+	    test_oom,
+	    test_remote_free,
+	    test_basic,
+	    test_alignment_and_size);
+}
diff --git a/test/integration/smallocx.sh b/test/integration/smallocx.sh
new file mode 100644
index 00000000..d07f10f3
--- /dev/null
+++ b/test/integration/smallocx.sh
@@ -0,0 +1,5 @@
+#!/bin/sh
+
+if [ "x${enable_fill}" = "x1" ] ; then
+    export MALLOC_CONF="junk:false"
+fi