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src/magazine_small.c libmalloc-116 libmalloc-374.60.3
--- libmalloc/libmalloc-116/src/magazine_small.c
+++ libmalloc/libmalloc-374.60.3/src/magazine_small.c
@@ -23,6 +23,7 @@
 
 #include "internal.h"
 
+
 /*********************	SMALL FREE LIST UTILITIES	************************/
 
 #pragma mark meta header helpers
@@ -38,6 +39,15 @@
 }
 
 /*
+ * Mark a block as not free, preserving its size.
+ */
+static MALLOC_INLINE void
+small_meta_header_set_not_free(msize_t *meta_headers, msize_t index)
+{
+	meta_headers[index] &= ~SMALL_IS_FREE;
+}
+
+/*
  * Mark a block as in use.  Only the first quantum of a block is marked thusly,
  * the remainder are marked "middle".
  */
@@ -56,21 +66,40 @@
 	meta_headers[index] = 0;
 }
 
+static MALLOC_INLINE MALLOC_ALWAYS_INLINE
+mag_index_t
+small_mag_get_thread_index(void)
+{
+#if CONFIG_SMALL_USES_HYPER_SHIFT
+	if (os_likely(_os_cpu_number_override == -1)) {
+		return _malloc_cpu_number() >> hyper_shift;
+	} else {
+		return _os_cpu_number_override >> hyper_shift;
+	}
+#else // CONFIG_SMALL_USES_HYPER_SHIFT
+	if (os_likely(_os_cpu_number_override == -1)) {
+		return _malloc_cpu_number();
+	} else {
+		return _os_cpu_number_override;
+	}
+#endif // CONFIG_SMALL_USES_HYPER_SHIFT
+}
+
 #pragma mark in-place free list
 
 static MALLOC_INLINE void
-small_inplace_checksum_ptr(szone_t *szone, inplace_linkage_s *linkage, void *ptr)
-{
-	uintptr_t checksum = free_list_gen_checksum((uintptr_t)ptr ^ szone->cookie ^ (uintptr_t)szone);
+small_inplace_checksum_ptr(rack_t *rack, inplace_linkage_s *linkage, void *ptr)
+{
+	uintptr_t checksum = free_list_gen_checksum((uintptr_t)ptr ^ rack->cookie ^ (uintptr_t)rack);
 	linkage->checksum = checksum;
 	linkage->ptr = ptr;
 }
 
 static MALLOC_INLINE free_list_t
-small_inplace_unchecksum_ptr(szone_t *szone, inplace_linkage_s *linkage)
-{
-	if (linkage->checksum != free_list_gen_checksum((uintptr_t)linkage->ptr ^ szone->cookie ^ (uintptr_t)szone)) {
-		free_list_checksum_botch(szone, linkage);
+small_inplace_unchecksum_ptr(rack_t *rack, inplace_linkage_s *linkage)
+{
+	if (linkage->checksum != (uint8_t)free_list_gen_checksum((uintptr_t)linkage->ptr ^ rack->cookie ^ (uintptr_t)rack)) {
+		free_list_checksum_botch(rack, linkage, linkage->ptr);
 		__builtin_trap();
 	}
 
@@ -78,27 +107,63 @@
 }
 
 static MALLOC_INLINE free_list_t
-small_inplace_free_entry_get_previous(szone_t *szone, small_inplace_free_entry_t ptr)
-{
-	return small_inplace_unchecksum_ptr(szone, &ptr->previous);
+small_inplace_unchecksum_ptr_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, rack_t *rack, inplace_linkage_s *linkage)
+{
+	inplace_linkage_s *mapped_linkage;
+	rack_t *mapped_rack;
+	if (reader(task, (vm_address_t)linkage, sizeof(*linkage),
+			(void **)&mapped_linkage)) {
+		printer("Unable to map small linkage pointer %p\n", linkage);
+		return (free_list_t){ .p = NULL };
+	}
+
+	if (reader(task, (vm_address_t)rack,
+			sizeof(struct rack_s), (void **)&mapped_rack)) {
+		printer("Failed to map small rack\n");
+		return (free_list_t){ .p = NULL };
+	}
+
+	if (mapped_linkage->checksum != (uint8_t)free_list_gen_checksum(
+			(uintptr_t)mapped_linkage->ptr ^ mapped_rack->cookie ^ (uintptr_t)rack)) {
+		free_list_checksum_botch(rack, linkage, mapped_linkage->ptr);
+		__builtin_trap();
+	}
+
+	return (free_list_t){ .p = mapped_linkage->ptr };
+}
+
+static MALLOC_INLINE free_list_t
+small_inplace_free_entry_get_previous(rack_t *rack, small_inplace_free_entry_t ptr)
+{
+	return small_inplace_unchecksum_ptr(rack, &ptr->previous);
 }
 
 static MALLOC_INLINE void
-small_inplace_free_entry_set_previous(szone_t *szone, small_inplace_free_entry_t entry, free_list_t previous)
-{
-	small_inplace_checksum_ptr(szone, &entry->previous, previous.p);
+small_inplace_free_entry_set_previous(rack_t *rack, small_inplace_free_entry_t entry, free_list_t previous)
+{
+	small_inplace_checksum_ptr(rack, &entry->previous, previous.p);
 }
 
 static MALLOC_INLINE free_list_t
-small_inplace_free_entry_get_next(szone_t *szone, small_inplace_free_entry_t ptr)
-{
-	return small_inplace_unchecksum_ptr(szone, &ptr->next);
+small_inplace_free_entry_get_next(rack_t *rack, small_inplace_free_entry_t ptr)
+{
+	return small_inplace_unchecksum_ptr(rack, &ptr->next);
+}
+
+static MALLOC_INLINE free_list_t
+small_inplace_free_entry_get_next_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, rack_t *rack,
+		small_inplace_free_entry_t ptr)
+{
+	return small_inplace_unchecksum_ptr_task(task, reader, printer, rack,
+			&ptr->next);
 }
 
 static MALLOC_INLINE void
-small_inplace_free_entry_set_next(szone_t *szone, small_inplace_free_entry_t entry, free_list_t next)
-{
-	small_inplace_checksum_ptr(szone, &entry->next, next.p);
+small_inplace_free_entry_set_next(rack_t *rack, small_inplace_free_entry_t entry, free_list_t next)
+{
+	small_inplace_checksum_ptr(rack, &entry->next, next.p);
 }
 
 #pragma mark OOB free list
@@ -145,21 +210,60 @@
 	return (free_list_t){ .p = (void *)oobe->next };
 }
 
+static MALLOC_INLINE free_list_t
+small_oob_free_entry_get_next_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, oob_free_entry_t oobe)
+{
+	oob_free_entry_t mapped_oobe;
+	if (reader(task, (vm_address_t)oobe, sizeof(*oobe),
+			(void **)&mapped_oobe)) {
+		printer("Failed to map small oobe pointer\n");
+		return (free_list_t){ .p = NULL };
+	}
+	return (free_list_t){ .p = (void *)mapped_oobe->next };
+}
+
 static MALLOC_INLINE void *
 small_oob_free_entry_get_ptr(oob_free_entry_t oobe)
 {
+	if (!(oobe->ptr & SMALL_IS_OOB)) {
+		return NULL;
+	}
 	small_region_t region = SMALL_REGION_FOR_PTR(oobe);
 	uint16_t block = oobe->ptr & ~SMALL_IS_OOB;
 	return (void *)((uintptr_t)region + (block << SHIFT_SMALL_QUANTUM));
 }
 
 static MALLOC_INLINE void *
+small_oob_free_entry_get_ptr_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, oob_free_entry_t oobe)
+{
+	// We need to map the oob_free_entry_t to read the pointer value.
+	oob_free_entry_t mapped_oobe;
+	if (reader(task, (vm_address_t)oobe, sizeof(*oobe),
+			(void **)&mapped_oobe)) {
+		printer("Failed to map small oobe pointer\n");
+		return NULL;
+	}
+
+	if (!(mapped_oobe->ptr & SMALL_IS_OOB)) {
+		return NULL;
+	}
+
+	// The rest of this code works with target process addresses and returns an
+	// address in the target process.
+	small_region_t region = SMALL_REGION_FOR_PTR(oobe);
+	uint16_t block = mapped_oobe->ptr & ~SMALL_IS_OOB;
+	return (void *)((uintptr_t)region + (block << SHIFT_SMALL_QUANTUM));
+}
+
+static MALLOC_INLINE void
 small_oob_free_entry_set_ptr(oob_free_entry_t oobe, void *ptr)
 {
-	oobe->ptr = SMALL_IS_OOB | (SMALL_OFFSET_FOR_PTR(ptr) >> SHIFT_SMALL_QUANTUM);
-}
-
-static MALLOC_INLINE void *
+	oobe->ptr = SMALL_IS_OOB | (SMALL_REGION_OFFSET_FOR_PTR(ptr) >> SHIFT_SMALL_QUANTUM);
+}
+
+static MALLOC_INLINE void
 small_oob_free_entry_set_free(oob_free_entry_t oobe)
 {
 	oobe->prev = ~0;
@@ -184,7 +288,7 @@
 	}
 
 #if DEBUG_MALLOC
-	malloc_printf("used all slots of OOB entries\n");
+	malloc_report(ASL_LEVEL_INFO, "used all slots of OOB entries\n");
 #endif
 	return NULL;
 }
@@ -198,7 +302,9 @@
 	// If this changes, then a linear search through the list may
 	// become an unsuitable choice.
 	for (int i=0; i < SMALL_OOB_COUNT; i++) {
-		if (small_oob_free_entry_get_ptr(&region->small_oob_free_entries[i]) == ptr) {
+		oob_free_entry_t oob = &region->small_oob_free_entries[i];
+		if (small_oob_free_entry_get_ptr(oob) == ptr &&
+				oob->ptr & SMALL_IS_OOB) {
 			return &region->small_oob_free_entries[i];
 		}
 	}
@@ -209,49 +315,62 @@
 #pragma mark generic free list
 
 static MALLOC_INLINE void
-small_free_list_set_previous(szone_t *szone, free_list_t entry, free_list_t previous)
+small_free_list_set_previous(rack_t *rack, free_list_t entry, free_list_t previous)
 {
 	if (small_is_oob_free_entry(entry)) {
 		small_oob_free_entry_set_previous(entry.oob, previous);
 	} else {
-		small_inplace_free_entry_set_previous(szone, entry.small_inplace, previous);
+		small_inplace_free_entry_set_previous(rack, entry.small_inplace, previous);
 	}
 }
 
 static MALLOC_INLINE free_list_t
-small_free_list_get_previous(szone_t *szone, free_list_t ptr)
+small_free_list_get_previous(rack_t *rack, free_list_t ptr)
 {
 	MALLOC_ASSERT(ptr.p);
 	if (small_is_oob_free_entry(ptr)) {
 		return small_oob_free_entry_get_previous(ptr.oob);
 	} else {
-		return small_inplace_free_entry_get_previous(szone, ptr.small_inplace);
+		return small_inplace_free_entry_get_previous(rack, ptr.small_inplace);
 	}
 }
 
 static MALLOC_INLINE void
-small_free_list_set_next(szone_t *szone, free_list_t entry, free_list_t next)
+small_free_list_set_next(rack_t *rack, free_list_t entry, free_list_t next)
 {
 	if (small_is_oob_free_entry(entry)) {
 		small_oob_free_entry_set_next(entry.oob, next);
 	} else {
-		small_inplace_free_entry_set_next(szone, entry.small_inplace, next);
+		small_inplace_free_entry_set_next(rack, entry.small_inplace, next);
 	}
 }
 
 static MALLOC_INLINE free_list_t
-small_free_list_get_next(szone_t *szone, free_list_t ptr)
+small_free_list_get_next(rack_t *rack, free_list_t ptr)
 {
 	MALLOC_ASSERT(ptr.p);
 	if (small_is_oob_free_entry(ptr)) {
 		return small_oob_free_entry_get_next(ptr.oob);
 	} else {
-		return small_inplace_free_entry_get_next(szone, ptr.small_inplace);
+		return small_inplace_free_entry_get_next(rack, ptr.small_inplace);
+	}
+}
+
+static MALLOC_INLINE free_list_t
+small_free_list_get_next_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, rack_t *rack, free_list_t ptr)
+{
+	MALLOC_ASSERT(ptr.p);
+	if (small_is_oob_free_entry(ptr)) {
+		return small_oob_free_entry_get_next_task(task, reader, printer, ptr.oob);
+	} else {
+		return small_inplace_free_entry_get_next_task(task, reader, printer,
+				rack, ptr.small_inplace);
 	}
 }
 
 static MALLOC_INLINE void *
-small_free_list_get_ptr(szone_t *szone, free_list_t ptr)
+small_free_list_get_ptr(free_list_t ptr)
 {
 	if (!ptr.p) {
 		return NULL;
@@ -262,10 +381,23 @@
 	}
 }
 
+static MALLOC_INLINE void *
+small_free_list_get_ptr_task(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, free_list_t ptr)
+{
+	if (!ptr.p) {
+		return NULL;
+	} else if (small_is_oob_free_entry(ptr)) {
+		return small_oob_free_entry_get_ptr_task(task, reader, printer, ptr.oob);
+	} else {
+		return (void *)ptr.p;
+	}
+}
+
 // Returns a free_list_t that is either inline or not based on the
 // pointer and msize.
 static MALLOC_INLINE free_list_t
-small_free_list_from_ptr(szone_t *szone, void *ptr, msize_t msize)
+small_free_list_from_ptr(rack_t *rack, void *ptr, msize_t msize)
 {
 	MALLOC_ASSERT(msize);
 
@@ -289,10 +421,10 @@
 }
 
 static MALLOC_INLINE void
-small_free_mark_free(szone_t *szone, free_list_t entry, msize_t msize)
+small_free_mark_free(rack_t *rack, free_list_t entry, msize_t msize)
 {
 	// Marks both the start and end block of a free-list entry as free.
-	void *ptr = small_free_list_get_ptr(szone, entry);
+	void *ptr = small_free_list_get_ptr(entry);
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
 	uintptr_t start_index = SMALL_META_INDEX_FOR_PTR(ptr);
 	uintptr_t end_index = SMALL_META_INDEX_FOR_PTR(ptr + SMALL_BYTES_FOR_MSIZE(msize) - 1);
@@ -303,26 +435,42 @@
 }
 
 static MALLOC_INLINE void
-small_free_mark_unfree(szone_t *szone, free_list_t entry, msize_t msize)
+small_free_mark_middle(rack_t *rack, free_list_t entry, msize_t msize)
 {
 	// Marks both the start and end block of a free-list entry as "middle" (unfree).
-	void *ptr = small_free_list_get_ptr(szone, entry);
+	void *ptr = small_free_list_get_ptr(entry);
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
 	uintptr_t start_index = SMALL_META_INDEX_FOR_PTR(ptr);
 	uintptr_t end_index = SMALL_META_INDEX_FOR_PTR(ptr + SMALL_BYTES_FOR_MSIZE(msize) - 1);
 	MALLOC_ASSERT(start_index <= end_index);
+	MALLOC_ASSERT((meta_headers[start_index] & ~SMALL_IS_FREE) == msize);
 
 	small_meta_header_set_middle(meta_headers, start_index);
 	small_meta_header_set_middle(meta_headers, end_index);
 }
 
+static MALLOC_INLINE void
+small_free_mark_unfree(rack_t *rack, free_list_t entry, msize_t msize)
+{
+	// Marks both the start and end block of a free-list entry as not free.
+	void *ptr = small_free_list_get_ptr(entry);
+	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
+	uintptr_t start_index = SMALL_META_INDEX_FOR_PTR(ptr);
+	uintptr_t end_index = SMALL_META_INDEX_FOR_PTR(ptr + SMALL_BYTES_FOR_MSIZE(msize) - 1);
+	MALLOC_ASSERT(start_index <= end_index);
+
+	small_meta_header_set_not_free(meta_headers, start_index);
+	small_meta_header_set_not_free(meta_headers, end_index);
+}
+
 static MALLOC_INLINE unsigned int
-small_free_list_count(szone_t *szone, free_list_t ptr)
+small_free_list_count(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, rack_t *rack, free_list_t ptr)
 {
 	unsigned int count = 0;
 	while (ptr.p) {
 		count++;
-		ptr = small_free_list_get_next(szone, ptr);
+		ptr = small_free_list_get_next_task(task, reader, printer, rack, ptr);
 	}
 	return count;
 }
@@ -333,43 +481,43 @@
  * Assumes szone has been locked
  */
 static free_list_t
-small_free_list_add_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
-{
-	grain_t slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
+small_free_list_add_ptr(rack_t *rack, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
+{
+	grain_t slot = SMALL_FREE_SLOT_FOR_MSIZE(rack, msize);
 	free_list_t free_head = small_mag_ptr->mag_free_list[slot];
 
 	// This will either return the free_list_t for the current pointer, or attempt
 	// to reserve an OOB entry for us.
-	free_list_t free_ptr = small_free_list_from_ptr(szone, ptr, msize);
+	free_list_t free_ptr = small_free_list_from_ptr(rack, ptr, msize);
 
 #if DEBUG_MALLOC
 	if (LOG(szone, ptr)) {
-		malloc_printf("in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
+		malloc_report(ASL_LEVEL_INFO, "in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
 	}
 	if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
-		szone_error(szone, 1, "small_free_list_add_ptr: Unaligned ptr", ptr, NULL);
-	}
-#endif
-
-	small_free_list_set_previous(szone, free_ptr, (free_list_t){ .p = NULL });
-	small_free_list_set_next(szone, free_ptr, free_head);
+		malloc_zone_error(rack->debug_flags, true, "small_free_list_add_ptr: Unaligned ptr %p\n", ptr);
+	}
+#endif
+
+	small_free_list_set_previous(rack, free_ptr, (free_list_t){ .p = NULL });
+	small_free_list_set_next(rack, free_ptr, free_head);
 
 	// Set the start and end blocks of the meta header as "free". Marking the last block
 	// allows coalescing the regions when we free adjacent regions.
-	small_free_mark_free(szone, free_ptr, msize);
-
-	if (small_free_list_get_ptr(szone, free_head)) {
+	small_free_mark_free(rack, free_ptr, msize);
+
+	if (small_free_list_get_ptr(free_head)) {
 #if DEBUG_MALLOC
 		if (small_free_list_get_previous(szone, free_head)) {
-			szone_error(szone, 1, "small_free_list_add_ptr: Internal invariant broken (free_head->previous != NULL)", ptr,
+			malloc_zone_error(rack->debug_flags, true, "small_free_list_add_ptr: Internal invariant broken (free_head->previous != NULL)\n"
 						"ptr=%p slot=%d free_head=%p previous=%p\n", ptr, slot, (void *)free_head, free_head->previous.p);
 		}
-		if (!SMALL_PTR_IS_FREE(small_free_list_get_ptr(szone, free_head))) {
-			szone_error(szone, 1, "small_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)", ptr,
-						"ptr=%p slot=%d free_head=%p\n", ptr, slot, (void *)small_free_list_get_ptr(szone, free_head));
-		}
-#endif
-		small_free_list_set_previous(szone, free_head, free_ptr);
+		if (!SMALL_PTR_IS_FREE(small_free_list_get_ptr(free_head))) {
+			malloc_zone_error(rack->debug_flags, true, "small_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)\n"
+						"ptr=%p slot=%d free_head=%p\n", ptr, slot, (void *)small_free_list_get_ptr(free_head));
+		}
+#endif
+		small_free_list_set_previous(rack, free_head, free_ptr);
 	} else {
 		BITMAPN_SET(small_mag_ptr->mag_bitmap, slot);
 	}
@@ -383,40 +531,57 @@
  * Assumes szone has been locked
  */
 static void
-small_free_list_remove_ptr_no_clear(szone_t *szone, magazine_t *small_mag_ptr, free_list_t entry, msize_t msize)
-{
-	grain_t slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
+small_free_list_remove_ptr_no_clear(rack_t *rack, magazine_t *small_mag_ptr, free_list_t entry, msize_t msize)
+{
+	grain_t slot = SMALL_FREE_SLOT_FOR_MSIZE(rack, msize);
 	free_list_t next, previous;
 
 #if DEBUG_MALLOC
 	if (LOG(szone, ptr)) {
-		malloc_printf("In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
-	}
-#endif
-
-	previous = small_free_list_get_previous(szone, entry);
-	next = small_free_list_get_next(szone, entry);
-
-	if (!small_free_list_get_ptr(szone, previous)) {
+		malloc_report(ASL_LEVEL_INFO, "In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
+	}
+#endif
+
+	previous = small_free_list_get_previous(rack, entry);
+	next = small_free_list_get_next(rack, entry);
+
+	if (!small_free_list_get_ptr(previous)) {
 		// The block to remove is the head of the free list
 #if DEBUG_MALLOC
 		if (small_mag_ptr->mag_free_list[slot] != ptr) {
-			szone_error(szone, 1, "small_free_list_remove_ptr: Internal invariant broken (small_mag_ptr->mag_free_list[slot])", ptr,
-						"ptr=%p slot=%d msize=%d small_mag_ptr->mag_free_list[slot]=%p\n", ptr, slot, msize,
-						(void *)small_mag_ptr->mag_free_list[slot]);
+			malloc_zone_error(rack->debug_flags, true,
+					"small_free_list_remove_ptr_no_clear: Internal invariant broken (small_mag_ptr->mag_free_list[slot])\n"
+					"ptr=%p slot=%d msize=%d small_mag_ptr->mag_free_list[slot]=%p\n", ptr, slot, msize,
+					(void *)small_mag_ptr->mag_free_list[slot]);
 			return;
 		}
 #endif
 		small_mag_ptr->mag_free_list[slot] = next;
-		if (!small_free_list_get_ptr(szone, next)) {
+		if (!small_free_list_get_ptr(next)) {
 			BITMAPN_CLR(small_mag_ptr->mag_bitmap, slot);
 		}
 	} else {
-		small_free_list_set_next(szone, previous, next);
-	}
-
-	if (small_free_list_get_ptr(szone, next)) {
-		small_free_list_set_previous(szone, next, previous);
+		// Check that the next pointer of "previous" points to "entry".
+		free_list_t prev_next = small_free_list_get_next(rack, previous);
+		if (small_free_list_get_ptr(prev_next) != small_free_list_get_ptr(entry)) {
+			malloc_zone_error(rack->debug_flags, true,
+					"small_free_list_remove_ptr_no_clear: Internal invariant broken (next ptr of prev) for %p, prev_next=%p\n",
+					small_free_list_get_ptr(entry), small_free_list_get_ptr(prev_next));
+			__builtin_unreachable(); // Always crashes in malloc_zone_error().
+		}
+		small_free_list_set_next(rack, previous, next);
+	}
+
+	if (small_free_list_get_ptr(next)) {
+		// Check that the previous pointer of "next" points to "entry".
+		free_list_t next_prev = small_free_list_get_previous(rack, next);
+		if (small_free_list_get_ptr(next_prev) != small_free_list_get_ptr(entry)) {
+			malloc_zone_error(rack->debug_flags, true,
+					"small_free_list_remove_ptr_no_clear: Internal invariant broken (prev ptr of next) for %p, next_prev=%p\n",
+					small_free_list_get_ptr(entry), small_free_list_get_ptr(next_prev));
+			__builtin_unreachable(); // Always crashes in malloc_zone_error().
+		}
+		small_free_list_set_previous(rack, next, previous);
 	}
 
 	if (small_is_oob_free_entry(entry)) {
@@ -425,22 +590,22 @@
 }
 
 static void
-small_free_list_remove_ptr(szone_t *szone, magazine_t *small_mag_ptr, free_list_t entry, msize_t msize)
+small_free_list_remove_ptr(rack_t *rack, magazine_t *small_mag_ptr, free_list_t entry, msize_t msize)
 {
 	// In the general case we want to ensure we marked these entries as "middle"
 	// while we are in this function. However, when we're moving free list entries
 	// from/to the recirc depot we rely on the metadata bits being intact to
 	// reconstruct the free list. In that case we have to be able to skip this
 	// metadata manipulation.
-	small_free_mark_unfree(szone, entry, msize);
-	small_free_list_remove_ptr_no_clear(szone, small_mag_ptr, entry, msize);
+	small_free_mark_middle(rack, entry, msize);
+	small_free_list_remove_ptr_no_clear(rack, small_mag_ptr, entry, msize);
 }
 
 // Find a free list entry by its pointer address. This should only really be used
 // by small_finalize_region, or similar, where the free_list_t entry of a known
 // pointer is desired. Otherwise it is cheaper to always pull off the free lists.
 static free_list_t
-small_free_list_find_by_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
+small_free_list_find_by_ptr(rack_t *rack, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
 {
 	if (*SMALL_METADATA_FOR_PTR(ptr) == (SMALL_IS_FREE | msize)) {
 		// If the block is marked free, and of size `msize`, then we first must check
@@ -462,12 +627,14 @@
 		return (free_list_t){ .p = ptr };
 	}
 
-	szone_error(szone, 1, "small_free_list_find_by_ptr: ptr is not free (ptr metadata !SMALL_IS_FREE)", ptr,
-				"ptr=%p msize=%d metadata=0x%x", ptr, msize, *SMALL_METADATA_FOR_PTR(ptr));
+	malloc_zone_error(rack->debug_flags, true,
+			"small_free_list_find_by_ptr: ptr is not free (ptr metadata !SMALL_IS_FREE), "
+			"ptr=%p msize=%d metadata=0x%x\n", ptr, msize, *SMALL_METADATA_FOR_PTR(ptr));
+	__builtin_trap();
 }
 
 void
-small_finalize_region(szone_t *szone, magazine_t *small_mag_ptr)
+small_finalize_region(rack_t *rack, magazine_t *small_mag_ptr)
 {
 	void *last_block, *previous_block;
 	msize_t last_msize, previous_msize, last_index;
@@ -489,7 +656,7 @@
 	//        than performing this workaround.
 	//
 	if (small_mag_ptr->mag_bytes_free_at_end) {
-		last_block = SMALL_REGION_END(small_mag_ptr->mag_last_region) - small_mag_ptr->mag_bytes_free_at_end;
+		last_block = SMALL_REGION_HEAP_END(small_mag_ptr->mag_last_region) - small_mag_ptr->mag_bytes_free_at_end;
 		last_msize = SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end);
 
 		last_index = SMALL_META_INDEX_FOR_PTR(last_block);
@@ -499,15 +666,15 @@
 			previous_block = (void *)((uintptr_t)last_block - SMALL_BYTES_FOR_MSIZE(previous_msize));
 
 			if (SMALL_PTR_IS_FREE(previous_block)) {
-				previous = small_free_list_find_by_ptr(szone, small_mag_ptr, previous_block, previous_msize);
-				small_free_list_remove_ptr(szone, small_mag_ptr, previous, previous_msize);
+				previous = small_free_list_find_by_ptr(rack, small_mag_ptr, previous_block, previous_msize);
+				small_free_list_remove_ptr(rack, small_mag_ptr, previous, previous_msize);
 				last_block = previous_block;
 				last_msize += previous_msize;
 			}
 		}
 
 		// splice last_block into the free list
-		small_free_list_add_ptr(szone, small_mag_ptr, last_block, last_msize);
+		small_free_list_add_ptr(rack, small_mag_ptr, last_block, last_msize);
 		small_mag_ptr->mag_bytes_free_at_end = 0;
 	}
 
@@ -515,19 +682,19 @@
 	free_list_t next;
 
 	if (small_mag_ptr->mag_bytes_free_at_start) {
-		last_block = SMALL_REGION_ADDRESS(small_mag_ptr->mag_last_region);
+		last_block = SMALL_REGION_HEAP_BASE(small_mag_ptr->mag_last_region);
 		last_msize = SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start);
 
 		void *next_block = (void *)((uintptr_t)last_block + small_mag_ptr->mag_bytes_free_at_start);
 		if (SMALL_PTR_IS_FREE(next_block)) {
 			msize_t next_msize = SMALL_PTR_SIZE(next_block);
-			next = small_free_list_find_by_ptr(szone, small_mag_ptr, next_block, next_msize);
-			small_free_list_remove_ptr(szone, small_mag_ptr, next, next_msize);
+			next = small_free_list_find_by_ptr(rack, small_mag_ptr, next_block, next_msize);
+			small_free_list_remove_ptr(rack, small_mag_ptr, next, next_msize);
 			last_msize += next_msize;
 		}
 
 		// splice last_block into the free list
-		small_free_list_add_ptr(szone, small_mag_ptr, last_block, last_msize);
+		small_free_list_add_ptr(rack, small_mag_ptr, last_block, last_msize);
 		small_mag_ptr->mag_bytes_free_at_start = 0;
 	}
 #endif
@@ -537,14 +704,13 @@
 }
 
 int
-small_free_detach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r)
-{
-	unsigned char *ptr = SMALL_REGION_ADDRESS(r);
-	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
-	uintptr_t start = (uintptr_t)SMALL_REGION_ADDRESS(r);
+small_free_detach_region(rack_t *rack, magazine_t *small_mag_ptr, region_t r)
+{
+	uintptr_t start = (uintptr_t)SMALL_REGION_HEAP_BASE(r);
 	uintptr_t current = start;
-	uintptr_t limit = (uintptr_t)SMALL_REGION_END(r);
+	uintptr_t limit = (uintptr_t)SMALL_REGION_HEAP_END(r);
 	int total_alloc = 0;
+	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(start);
 
 	while (current < limit) {
 		unsigned index = SMALL_META_INDEX_FOR_PTR(current);
@@ -555,14 +721,14 @@
 		if (!msize) {
 #if DEBUG_MALLOC
 			boolean_t is_free = msize_and_free & SMALL_IS_FREE;
-			malloc_printf("*** small_free_detach_region error with %p: msize=%d is_free =%d\n", (void *)current, msize, is_free);
+			malloc_report(ASL_LEVEL_ERR, "*** small_free_detach_region error with %p: msize=%d is_free=%d\n", (void *)current, msize, is_free);
 #endif
 			break;
 		}
 
 		if (is_free) {
-			free_list_t entry = small_free_list_find_by_ptr(szone, small_mag_ptr, (void *)current, msize);
-			small_free_list_remove_ptr_no_clear(szone, small_mag_ptr, entry, msize);
+			free_list_t entry = small_free_list_find_by_ptr(rack, small_mag_ptr, (void *)current, msize);
+			small_free_list_remove_ptr_no_clear(rack, small_mag_ptr, entry, msize);
 		} else {
 			total_alloc++;
 		}
@@ -572,14 +738,13 @@
 }
 
 size_t
-small_free_reattach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r)
-{
-	unsigned char *ptr = SMALL_REGION_ADDRESS(r);
-	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
-	uintptr_t start = (uintptr_t)SMALL_REGION_ADDRESS(r);
+small_free_reattach_region(rack_t *rack, magazine_t *small_mag_ptr, region_t r)
+{
+	uintptr_t start = (uintptr_t)SMALL_REGION_HEAP_BASE(r);
 	uintptr_t current = start;
-	uintptr_t limit = (uintptr_t)SMALL_REGION_END(r);
+	uintptr_t limit = (uintptr_t)SMALL_REGION_HEAP_END(r);
 	size_t total_alloc = 0;
+	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(start);
 
 	while (current < limit) {
 		unsigned index = SMALL_META_INDEX_FOR_PTR(current);
@@ -589,12 +754,12 @@
 
 		if (!msize) {
 #if DEBUG_MALLOC
-			malloc_printf("*** small_free_reattach_region error with %p: msize=%d is_free =%d\n", (void *)current, msize, is_free);
+			malloc_report(ASL_LEVEL_ERR, "*** small_free_reattach_region error with %p: msize=%d is_free=%d\n", (void *)current, msize, is_free);
 #endif
 			break;
 		}
 		if (is_free) {
-			small_free_list_add_ptr(szone, small_mag_ptr, (void *)current, msize);
+			small_free_list_add_ptr(rack, small_mag_ptr, (void *)current, msize);
 		} else {
 			total_alloc += SMALL_BYTES_FOR_MSIZE(msize);
 		}
@@ -608,13 +773,13 @@
 } small_pg_pair_t;
 
 void
-small_free_scan_madvise_free(szone_t *szone, magazine_t *depot_ptr, region_t r)
-{
-	uintptr_t start = (uintptr_t)SMALL_REGION_ADDRESS(r);
+small_free_scan_madvise_free(rack_t *rack, magazine_t *depot_ptr, region_t r)
+{
+	uintptr_t start = (uintptr_t)SMALL_REGION_HEAP_BASE(r);
 	uintptr_t current = start;
-	uintptr_t limit = (uintptr_t)SMALL_REGION_END(r);
+	uintptr_t limit = (uintptr_t)SMALL_REGION_HEAP_END(r);
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(start);
-	small_pg_pair_t advisory[((SMALL_REGION_PAYLOAD_BYTES + vm_kernel_page_size - 1) >> vm_kernel_page_shift) >>
+	small_pg_pair_t advisory[((SMALL_HEAP_SIZE + vm_kernel_page_size - 1) >> vm_kernel_page_shift) >>
 							 1]; // 4096bytes stack allocated
 	int advisories = 0;
 
@@ -629,7 +794,7 @@
 		if (is_free && !msize && (current == start)) {
 #if DEBUG_MALLOC
 			// first block is all free
-			malloc_printf("*** small_free_scan_madvise_free first block is all free! %p: msize=%d is_free =%d\n", (void *)current,
+			malloc_report(ASL_LEVEL_ERR, "*** small_free_scan_madvise_free first block is all free! %p: msize=%d is_free=%d\n", (void *)current,
 						  msize, is_free);
 #endif
 			uintptr_t pgLo = round_page_kernel(start + sizeof(free_list_t) + sizeof(msize_t));
@@ -644,8 +809,8 @@
 		}
 		if (!msize) {
 #if DEBUG_MALLOC
-			malloc_printf(
-						  "*** small_free_scan_madvise_free error with %p: msize=%d is_free =%d\n", (void *)current, msize, is_free);
+			malloc_report(ASL_LEVEL_ERR,
+						  "*** small_free_scan_madvise_free error with %p: msize=%d is_free=%d\n", (void *)current, msize, is_free);
 #endif
 			break;
 		}
@@ -654,7 +819,7 @@
 			uintptr_t pgHi = trunc_page_kernel(current + SMALL_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));
 
 			if (pgLo < pgHi) {
-				advisory[advisories].pnum = (pgLo - start) >> vm_kernel_page_shift;
+				advisory[advisories].pnum = (pgLo - (uintptr_t)r) >> vm_kernel_page_shift;
 				advisory[advisories].size = (pgHi - pgLo) >> vm_kernel_page_shift;
 				advisories++;
 			}
@@ -666,23 +831,24 @@
 		int i;
 
 		OSAtomicIncrement32Barrier(&(REGION_TRAILER_FOR_SMALL_REGION(r)->pinned_to_depot));
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(depot_ptr);
 		for (i = 0; i < advisories; ++i) {
-			uintptr_t addr = (advisory[i].pnum << vm_page_quanta_shift) + start;
+			uintptr_t addr = (advisory[i].pnum << vm_page_quanta_shift) + (uintptr_t)r;
 			size_t size = advisory[i].size << vm_page_quanta_shift;
 
-			madvise_free_range(szone, r, addr, addr + size, NULL);
-		}
-		SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
+			mvm_madvise_free(rack, r, addr, addr + size, NULL, rack->debug_flags & MALLOC_DO_SCRIBBLE);
+		}
+		SZONE_MAGAZINE_PTR_LOCK(depot_ptr);
 		OSAtomicDecrement32Barrier(&(REGION_TRAILER_FOR_SMALL_REGION(r)->pinned_to_depot));
 	}
 }
 
+#if CONFIG_RECIRC_DEPOT
 static region_t
-small_find_msize_region(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
+small_find_msize_region(rack_t *rack, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
 {
 	void *ptr;
-	grain_t slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
+	grain_t slot = SMALL_FREE_SLOT_FOR_MSIZE(rack, msize);
 	free_list_t *free_list = small_mag_ptr->mag_free_list;
 	free_list_t *the_slot = free_list + slot;
 	free_list_t *limit;
@@ -692,59 +858,52 @@
 	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);
 
 	// Look for an exact match by checking the freelist for this msize.
-	ptr = small_free_list_get_ptr(szone, *the_slot);
+	ptr = small_free_list_get_ptr(*the_slot);
 	if (ptr) {
 		return SMALL_REGION_FOR_PTR(ptr);
 	}
 
 	// Mask off the bits representing slots holding free blocks smaller than
 	// the size we need.
-	if (szone->is_largemem) {
-		// BITMAPN_CTZ implementation
-		unsigned idx = slot >> 5;
-		bitmap = 0;
-		unsigned mask = ~((1 << (slot & 31)) - 1);
-		for (; idx < SMALL_BITMAP_WORDS; ++idx) {
-			bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
-			if (bitmap != 0) {
-				break;
-			}
-			mask = ~0U;
-		}
-		// Check for fallthrough: No bits set in bitmap
-		if ((bitmap == 0) && (idx == SMALL_BITMAP_WORDS)) {
-			return NULL;
-		}
-
-		// Start looking at the first set bit, plus 32 bits for every word of
-		// zeroes or entries that were too small.
-		slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
-	} else {
-		bitmap = small_mag_ptr->mag_bitmap[0] & ~((1 << slot) - 1);
-		if (!bitmap) {
-			return NULL;
-		}
-
-		slot = BITMAP32_CTZ((&bitmap));
-	}
-	limit = free_list + szone->num_small_slots - 1;
+	//
+	// BITMAPN_CTZ implementation
+	unsigned idx = slot >> 5;
+	bitmap = 0;
+	unsigned mask = ~((1 << (slot & 31)) - 1);
+	for (; idx < SMALL_FREELIST_BITMAP_WORDS(rack); ++idx) {
+		bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
+		if (bitmap != 0) {
+			break;
+		}
+		mask = ~0U;
+	}
+	// Check for fallthrough: No bits set in bitmap
+	if ((bitmap == 0) && (idx == SMALL_FREELIST_BITMAP_WORDS(rack))) {
+		return NULL;
+	}
+
+	// Start looking at the first set bit, plus 32 bits for every word of
+	// zeroes or entries that were too small.
+	slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
+
+	limit = free_list + SMALL_FREE_SLOT_COUNT(rack) - 1;
 	free_list += slot;
 
 	if (free_list < limit) {
-		ptr = small_free_list_get_ptr(szone, *free_list);
+		ptr = small_free_list_get_ptr(*free_list);
 		if (ptr) {
 			return SMALL_REGION_FOR_PTR(ptr);
 		} else {
 			/* Shouldn't happen. Fall through to look at last slot. */
 #if DEBUG_MALLOC
-			malloc_printf("in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n", slot);
+			malloc_report(ASL_LEVEL_ERR, "in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n", slot);
 #endif
 		}
 	}
 
 	// We are now looking at the last slot, which contains blocks equal to, or
 	// due to coalescing of free blocks, larger than (num_small_slots - 1) * (small quantum size).
-	ptr = small_free_list_get_ptr(szone, *limit);
+	ptr = small_free_list_get_ptr(*limit);
 	if (ptr) {
 		return SMALL_REGION_FOR_PTR(ptr);
 	}
@@ -753,84 +912,191 @@
 }
 
 static boolean_t
-small_get_region_from_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
-{
-	magazine_t *depot_ptr = &(szone->small_magazines[DEPOT_MAGAZINE_INDEX]);
+small_get_region_from_depot(rack_t *rack, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
+{
+	magazine_t *depot_ptr = &(rack->magazines[DEPOT_MAGAZINE_INDEX]);
 
 	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
-	if (szone->num_small_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
+	if (rack->num_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
 		return 0;
 	}
 
 #if DEBUG_MALLOC
 	if (DEPOT_MAGAZINE_INDEX == mag_index) {
-		szone_error(szone, 1, "small_get_region_from_depot called for magazine index -1", NULL, NULL);
+		malloc_zone_error(rack->debug_flags, true, "small_get_region_from_depot called for magazine index -1\n", NULL, NULL);
 		return 0;
 	}
 #endif
 
-	SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
+	SZONE_MAGAZINE_PTR_LOCK(depot_ptr);
 
 	// Appropriate a Depot'd region that can satisfy requested msize.
 	region_trailer_t *node;
 	region_t sparse_region;
+	msize_t try_msize = msize;
 
 	while (1) {
-		sparse_region = small_find_msize_region(szone, depot_ptr, DEPOT_MAGAZINE_INDEX, msize);
+		sparse_region = small_find_msize_region(rack, depot_ptr, DEPOT_MAGAZINE_INDEX, try_msize);
 		if (NULL == sparse_region) { // Depot empty?
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(depot_ptr);
 			return 0;
 		}
 
 		node = REGION_TRAILER_FOR_SMALL_REGION(sparse_region);
-		if (0 >= node->pinned_to_depot) {
+		if (0 == node->pinned_to_depot) {
+			// Found one!
 			break;
 		}
 
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
-		yield();
-		SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
+		// Try the next msize up - maybe the head of its free list will be in
+		// a region we can use. Once we get the region we'll still allocate the
+		// original msize.
+		try_msize++;
+
+		if (try_msize > NUM_SMALL_SLOTS) {
+			// Tried all the msizes but couldn't get a usable region. Let's
+			// give up for now and we'll allocate a new region from the kernel.
+			SZONE_MAGAZINE_PTR_UNLOCK(depot_ptr);
+			return 0;
+		}
 	}
 
 	// disconnect node from Depot
-	recirc_list_extract(szone, depot_ptr, node);
+	recirc_list_extract(rack, depot_ptr, node);
 
 	// Iterate the region pulling its free entries off the (locked) Depot's free list
-	int objects_in_use = small_free_detach_region(szone, depot_ptr, sparse_region);
+	int objects_in_use = small_free_detach_region(rack, depot_ptr, sparse_region);
 
 	// Transfer ownership of the region
 	MAGAZINE_INDEX_FOR_SMALL_REGION(sparse_region) = mag_index;
-	node->pinned_to_depot = 0;
+	MALLOC_ASSERT(node->pinned_to_depot == 0);
 
 	// Iterate the region putting its free entries on its new (locked) magazine's free list
-	size_t bytes_inplay = small_free_reattach_region(szone, small_mag_ptr, sparse_region);
+	size_t bytes_inplay = small_free_reattach_region(rack, small_mag_ptr, sparse_region);
 
 	depot_ptr->mag_num_bytes_in_objects -= bytes_inplay;
-	depot_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
+	depot_ptr->num_bytes_in_magazine -= SMALL_HEAP_SIZE;
 	depot_ptr->mag_num_objects -= objects_in_use;
 
 	small_mag_ptr->mag_num_bytes_in_objects += bytes_inplay;
-	small_mag_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
+	small_mag_ptr->num_bytes_in_magazine += SMALL_HEAP_SIZE;
 	small_mag_ptr->mag_num_objects += objects_in_use;
 
-	// connect to magazine as first node
-	recirc_list_splice_first(szone, small_mag_ptr, node);
-
-	SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
-
-	// madvise() outside the Depot lock
-	(void)madvise_reuse_range(
-							  szone, sparse_region, (uintptr_t)sparse_region, (uintptr_t)sparse_region + SMALL_REGION_PAYLOAD_BYTES);
-
-	MAGMALLOC_DEPOTREGION((void *)szone, (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
+	// connect to magazine as last node
+	recirc_list_splice_last(rack, small_mag_ptr, node);
+
+	SZONE_MAGAZINE_PTR_UNLOCK(depot_ptr);
+
+	MAGMALLOC_DEPOTREGION(SMALL_SZONE_FROM_RACK(rack), (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
 						  (int)BYTES_USED_FOR_SMALL_REGION(sparse_region)); // DTrace USDT Probe
 
 	return 1;
 }
+#endif // CONFIG_RECIRC_DEPOT
+
+#if CONFIG_MADVISE_PRESSURE_RELIEF
+void
+small_madvise_pressure_relief(rack_t *rack)
+{
+	mag_index_t mag_index;
+	magazine_t *small_depot_ptr = &rack->magazines[DEPOT_MAGAZINE_INDEX];
+
+	for (mag_index = 0; mag_index < rack->num_magazines; mag_index++) {
+		size_t index;
+		for (index = 0; index < rack->region_generation->num_regions_allocated; ++index) {
+			rack_region_lock(rack);
+
+			region_t small = rack->region_generation->hashed_regions[index];
+			if (!small || small == HASHRING_REGION_DEALLOCATED) {
+				rack_region_unlock(rack);
+				continue;
+			}
+
+			region_trailer_t *trailer = REGION_TRAILER_FOR_SMALL_REGION(small);
+			// Make sure that the owning magazine doesn't try and take this out
+			// from under our feet.
+			trailer->dispose_flags |= RACK_DISPOSE_DELAY;
+			rack_region_unlock(rack);
+
+			magazine_t *mag_ptr = mag_lock_zine_for_region_trailer(rack->magazines,
+					trailer, MAGAZINE_INDEX_FOR_SMALL_REGION(small));
+
+			// If acquiring the region lock was enough to prevent the owning
+			// magazine from deallocating the region, free it now so we don't
+			// do wasted work.
+			if (rack_region_maybe_dispose(rack, small, SMALL_REGION_SIZE, trailer)) {
+				SZONE_MAGAZINE_PTR_UNLOCK(mag_ptr);
+				continue;
+			}
+
+			/* Ordering is important here, the magazine of a region may potentially change
+			 * during mag_lock_zine_for_region_trailer, so src_mag_index must be taken
+			 * after we've obtained the lock.
+			 */
+			mag_index_t src_mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(small);
+
+			/* We can (and must) ignore magazines that are already in the recirc depot. */
+			if (src_mag_index == DEPOT_MAGAZINE_INDEX) {
+				SZONE_MAGAZINE_PTR_UNLOCK(mag_ptr);
+				continue;
+			}
+
+			if (REGION_TRAILER_FOR_SMALL_REGION(small)->pinned_to_depot > 0) {
+				SZONE_MAGAZINE_PTR_UNLOCK(mag_ptr);
+				continue;
+			}
+
+			if (small == mag_ptr->mag_last_region && (mag_ptr->mag_bytes_free_at_end || mag_ptr->mag_bytes_free_at_start)) {
+				small_finalize_region(rack, mag_ptr);
+			}
+
+			/* Because this region is currently in use, we can't safely madvise it while
+			 * it's attached to the magazine. For this operation we have to remove it from
+			 * the current mag, attach it to the depot and then madvise.
+			 */
+
+			recirc_list_extract(rack, mag_ptr, REGION_TRAILER_FOR_SMALL_REGION(small));
+			int objects_in_use = small_free_detach_region(rack, mag_ptr, small);
+
+			SZONE_MAGAZINE_PTR_LOCK(small_depot_ptr);
+			MAGAZINE_INDEX_FOR_SMALL_REGION(small) = DEPOT_MAGAZINE_INDEX;
+			MALLOC_ASSERT(REGION_TRAILER_FOR_SMALL_REGION(small)->pinned_to_depot == 0);
+
+			size_t bytes_inplay = small_free_reattach_region(rack, small_depot_ptr, small);
+
+			/* Fix up the metadata of the target magazine while the region is in the depot. */
+			mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
+			mag_ptr->num_bytes_in_magazine -= SMALL_HEAP_SIZE;
+			mag_ptr->mag_num_objects -= objects_in_use;
+
+			/* Now we can drop the magazine lock of the source mag. */
+			SZONE_MAGAZINE_PTR_UNLOCK(mag_ptr);
+
+			small_depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
+			small_depot_ptr->num_bytes_in_magazine += SMALL_HEAP_SIZE;
+			small_depot_ptr->mag_num_objects -= objects_in_use;
+
+			recirc_list_splice_last(rack, small_depot_ptr, REGION_TRAILER_FOR_SMALL_REGION(small));
+
+			/* Actually do the scan, done holding the depot lock, the call will drop the lock
+			 * around the actual madvise syscalls.
+			 */
+			small_free_scan_madvise_free(rack, small_depot_ptr, small);
+
+			/* Now the region is in the recirc depot, the next allocations to require more
+			 * blocks will come along and take one of these regions back out of the depot.
+			 * As OS X madvise's reuse on an per-region basis, we leave as many of these
+			 * regions in the depot as possible after memory pressure.
+			 */
+			SZONE_MAGAZINE_PTR_UNLOCK(small_depot_ptr);
+		}
+	}
+}
+#endif // CONFIG_MADVISE_PRESSURE_RELIEF
 
 #if CONFIG_AGGRESSIVE_MADVISE || CONFIG_RECIRC_DEPOT
 static MALLOC_INLINE void
-small_madvise_free_range_no_lock(szone_t *szone,
+small_madvise_free_range_no_lock(rack_t *rack,
 								 magazine_t *small_mag_ptr,
 								 region_t region,
 								 free_list_t freee,
@@ -838,7 +1104,7 @@
 								 void *headptr,
 								 size_t headsize)
 {
-	void *ptr = small_free_list_get_ptr(szone, freee);
+	void *ptr = small_free_list_get_ptr(freee);
 	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(region);
 
 	// Lock on small_magazines[mag_index] is already held here.
@@ -870,13 +1136,19 @@
 		uintptr_t free_hi = MIN(trunc_extent, hi);
 
 		if (free_lo < free_hi) {
-			small_free_list_remove_ptr(szone, small_mag_ptr, freee, fmsize);
+			// Before unlocking, ensure that the metadata for the freed region
+			// makes it look not free but includes the length. This ensures that
+			// any code that inspects the metadata while we are unlocked sees
+			// a valid state and will not try to use or coalesce freed memory
+			// into it.
+			small_free_mark_unfree(rack, freee, fmsize);
+			small_free_list_remove_ptr_no_clear(rack, small_mag_ptr, freee, fmsize);
 			OSAtomicIncrement32Barrier(&(node->pinned_to_depot));
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-			madvise_free_range(szone, region, free_lo, free_hi, &szone->last_small_advise);
-			SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+			mvm_madvise_free(rack, region, free_lo, free_hi, &rack->last_madvise, rack->debug_flags & MALLOC_DO_SCRIBBLE);
+			SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
 			OSAtomicDecrement32Barrier(&(node->pinned_to_depot));
-			small_free_list_add_ptr(szone, small_mag_ptr, ptr, fmsize);
+			small_free_list_add_ptr(rack, small_mag_ptr, ptr, fmsize);
 		}
 	}
 }
@@ -884,60 +1156,53 @@
 
 #if CONFIG_RECIRC_DEPOT
 static region_t
-small_free_try_depot_unmap_no_lock(szone_t *szone, magazine_t *depot_ptr, region_trailer_t *node)
-{
-	if (0 < node->bytes_used || 0 < node->pinned_to_depot || depot_ptr->recirculation_entries < (szone->num_small_magazines * 2)) {
+small_free_try_depot_unmap_no_lock(rack_t *rack, magazine_t *depot_ptr, region_trailer_t *node)
+{
+	if (0 < node->bytes_used || 0 < node->pinned_to_depot || depot_ptr->recirculation_entries < recirc_retained_regions) {
 		return NULL;
 	}
 
 	// disconnect first node from Depot
-	recirc_list_extract(szone, depot_ptr, node);
+	recirc_list_extract(rack, depot_ptr, node);
 
 	// Iterate the region pulling its free entries off the (locked) Depot's free list
 	region_t sparse_region = SMALL_REGION_FOR_PTR(node);
-	int objects_in_use = small_free_detach_region(szone, depot_ptr, sparse_region);
+	int objects_in_use = small_free_detach_region(rack, depot_ptr, sparse_region);
 
 	if (0 == objects_in_use) {
-		// Invalidate the hash table entry for this region with HASHRING_REGION_DEALLOCATED.
-		// Using HASHRING_REGION_DEALLOCATED preserves the collision chain, using HASHRING_OPEN_ENTRY (0) would not.
-		rgnhdl_t pSlot = hash_lookup_region_no_lock(szone->small_region_generation->hashed_regions,
-													szone->small_region_generation->num_regions_allocated, szone->small_region_generation->num_regions_allocated_shift,
-													sparse_region);
-		if (NULL == pSlot) {
-			szone_error(szone, 1, "small_free_try_depot_unmap_no_lock hash lookup failed:", NULL, "%p\n", sparse_region);
+		if (!rack_region_remove(rack, sparse_region, node)) {
 			return NULL;
 		}
-		*pSlot = HASHRING_REGION_DEALLOCATED;
-		depot_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
-		__sync_fetch_and_add(&(szone->num_small_regions_dealloc), 1); // Atomically increment num_small_regions_dealloc
+		depot_ptr->num_bytes_in_magazine -= SMALL_HEAP_SIZE;
 
 		// Caller will transfer ownership of the region back to the OS with no locks held
-		MAGMALLOC_DEALLOCREGION((void *)szone, (void *)sparse_region, SMALL_REGION_SIZE); // DTrace USDT Probe
+		MAGMALLOC_DEALLOCREGION(SMALL_SZONE_FROM_RACK(rack), (void *)sparse_region, (int)SMALL_REGION_SIZE); // DTrace USDT Probe
 		return sparse_region;
 
 	} else {
-		szone_error(szone, 1, "small_free_try_depot_unmap_no_lock objects_in_use not zero:", NULL, "%d\n", objects_in_use);
+		malloc_zone_error(rack->debug_flags, true,
+				"small_free_try_depot_unmap_no_lock objects_in_use not zero: %d\n", objects_in_use);
 		return NULL;
 	}
 }
 
 static boolean_t
-small_free_do_recirc_to_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index)
+small_free_do_recirc_to_depot(rack_t *rack, magazine_t *small_mag_ptr, mag_index_t mag_index)
 {
 	// The entire magazine crossed the "emptiness threshold". Transfer a region
 	// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
 	// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.
 	region_trailer_t *node = small_mag_ptr->firstNode;
 
-	while (node && !node->recirc_suitable) {
+	while (node && (!node->recirc_suitable || node->pinned_to_depot)) {
 		node = node->next;
 	}
 
 	if (NULL == node) {
 #if DEBUG_MALLOC
-		malloc_printf("*** small_free_do_recirc_to_depot end of list\n");
-#endif
-		return TRUE; // Caller must SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		malloc_report(ASL_LEVEL_ERR, "*** small_free_do_recirc_to_depot end of list\n");
+#endif
+		return TRUE; // Caller must SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 	}
 
 	region_t sparse_region = SMALL_REGION_FOR_PTR(node);
@@ -945,58 +1210,62 @@
 	// Deal with unclaimed memory -- mag_bytes_free_at_end or mag_bytes_free_at start
 	if (sparse_region == small_mag_ptr->mag_last_region &&
 		(small_mag_ptr->mag_bytes_free_at_end || small_mag_ptr->mag_bytes_free_at_start)) {
-		small_finalize_region(szone, small_mag_ptr);
+		small_finalize_region(rack, small_mag_ptr);
 	}
 
 	// disconnect "suitable" node from magazine
-	recirc_list_extract(szone, small_mag_ptr, node);
+	recirc_list_extract(rack, small_mag_ptr, node);
 
 	// Iterate the region pulling its free entries off its (locked) magazine's free list
-	int objects_in_use = small_free_detach_region(szone, small_mag_ptr, sparse_region);
-	magazine_t *depot_ptr = &(szone->small_magazines[DEPOT_MAGAZINE_INDEX]);
+	int objects_in_use = small_free_detach_region(rack, small_mag_ptr, sparse_region);
+	magazine_t *depot_ptr = &(rack->magazines[DEPOT_MAGAZINE_INDEX]);
 
 	// hand over the region to the (locked) Depot
-	SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
+	SZONE_MAGAZINE_PTR_LOCK(depot_ptr);
 	// this will cause small_free_list_add_ptr called by small_free_reattach_region to use
 	// the depot as its target magazine, rather than magazine formerly associated with sparse_region
 	MAGAZINE_INDEX_FOR_SMALL_REGION(sparse_region) = DEPOT_MAGAZINE_INDEX;
 	node->pinned_to_depot = 0;
 
 	// Iterate the region putting its free entries on Depot's free list
-	size_t bytes_inplay = small_free_reattach_region(szone, depot_ptr, sparse_region);
+	size_t bytes_inplay = small_free_reattach_region(rack, depot_ptr, sparse_region);
 
 	small_mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
-	small_mag_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
+	small_mag_ptr->num_bytes_in_magazine -= SMALL_HEAP_SIZE;
 	small_mag_ptr->mag_num_objects -= objects_in_use;
 
-	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr); // Unlock the originating magazine
+	SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr); // Unlock the originating magazine
 
 	depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
-	depot_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
+	depot_ptr->num_bytes_in_magazine += SMALL_HEAP_SIZE;
 	depot_ptr->mag_num_objects += objects_in_use;
 
 	// connect to Depot as last node
-	recirc_list_splice_last(szone, depot_ptr, node);
-
-	MAGMALLOC_RECIRCREGION((void *)szone, (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
+	recirc_list_splice_last(rack, depot_ptr, node);
+
+	MAGMALLOC_RECIRCREGION(SMALL_SZONE_FROM_RACK(rack), (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
 						   (int)BYTES_USED_FOR_SMALL_REGION(sparse_region)); // DTrace USDT Probe
 
-#if !CONFIG_AGGRESSIVE_MADVISE
-	// Mark free'd dirty pages with MADV_FREE to reduce memory pressure
-	small_free_scan_madvise_free(szone, depot_ptr, sparse_region);
-#endif
+#if CONFIG_AGGRESSIVE_MADVISE
+	if (!aggressive_madvise_enabled)
+#endif
+	{
+		// Mark free'd dirty pages with MADV_FREE to reduce memory pressure
+		small_free_scan_madvise_free(rack, depot_ptr, sparse_region);
+	}
 
 	// If the region is entirely empty vm_deallocate() it outside the depot lock
-	region_t r_dealloc = small_free_try_depot_unmap_no_lock(szone, depot_ptr, node);
-	SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
+	region_t r_dealloc = small_free_try_depot_unmap_no_lock(rack, depot_ptr, node);
+	SZONE_MAGAZINE_PTR_UNLOCK(depot_ptr);
 	if (r_dealloc) {
-		deallocate_pages(szone, r_dealloc, SMALL_REGION_SIZE, 0);
+		mvm_deallocate_pages(r_dealloc, SMALL_REGION_SIZE,
+				MALLOC_FIX_GUARD_PAGE_FLAGS(rack->debug_flags));
 	}
 	return FALSE; // Caller need not unlock the originating magazine
 }
 
 static MALLOC_INLINE boolean_t
-small_free_try_recirc_to_depot(szone_t *szone,
+small_free_try_recirc_to_depot(rack_t *rack,
 							   magazine_t *small_mag_ptr,
 							   mag_index_t mag_index,
 							   region_t region,
@@ -1009,12 +1278,12 @@
 	size_t bytes_used = node->bytes_used;
 
 	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
-	if (szone->num_small_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
+	if (rack->num_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
 		/* NOTHING */
-		return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr)
+		return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(tiny_mag_ptr)
 	} else if (DEPOT_MAGAZINE_INDEX != mag_index) {
 		// Emptiness discriminant
-		if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
+		if (small_region_below_recirc_threshold(region)) {
 			/* Region has crossed threshold from density to sparsity. Mark it "suitable" on the
 			 * recirculation candidates list. */
 			node->recirc_suitable = TRUE;
@@ -1026,20 +1295,18 @@
 		// Has the entire magazine crossed the "emptiness threshold"? If so, transfer a region
 		// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
 		// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.
-
-		size_t a = small_mag_ptr->num_bytes_in_magazine;	// Total bytes allocated to this magazine
-		size_t u = small_mag_ptr->mag_num_bytes_in_objects; // In use (malloc'd) from this magaqzine
-
-		if (a - u > ((3 * SMALL_REGION_PAYLOAD_BYTES) / 2) && u < DENSITY_THRESHOLD(a)) {
-			return small_free_do_recirc_to_depot(szone, small_mag_ptr, mag_index);
-		}
-
+		if (small_magazine_below_recirc_threshold(small_mag_ptr)) {
+			return small_free_do_recirc_to_depot(rack, small_mag_ptr, mag_index);
+		}
 	} else {
-#if !CONFIG_AGGRESSIVE_MADVISE
-		// We are free'ing into the depot, so madvise as we do so unless we were madvising every incoming
-		// allocation anyway.
-		small_madvise_free_range_no_lock(szone, small_mag_ptr, region, freee, msize, headptr, headsize);
-#endif
+#if CONFIG_AGGRESSIVE_MADVISE
+		if (!aggressive_madvise_enabled)
+#endif
+		{
+			// We are free'ing into the depot, so madvise as we do so unless we were madvising every incoming
+			// allocation anyway.
+			small_madvise_free_range_no_lock(rack, small_mag_ptr, region, freee, msize, headptr, headsize);
+		}
 
 		if (0 < bytes_used || 0 < node->pinned_to_depot) {
 			/* Depot'd region is still live. Leave it in place on the Depot's recirculation list
@@ -1047,54 +1314,58 @@
 			 * with detach_region/reattach_region */
 		} else {
 			/* Depot'd region is just now empty. Consider return to OS. */
-			region_t r_dealloc = small_free_try_depot_unmap_no_lock(szone, small_mag_ptr, node);
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			region_t r_dealloc = small_free_try_depot_unmap_no_lock(rack, small_mag_ptr, node);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 			if (r_dealloc) {
-				deallocate_pages(szone, r_dealloc, SMALL_REGION_SIZE, 0);
+				mvm_deallocate_pages(r_dealloc, SMALL_REGION_SIZE, MALLOC_FIX_GUARD_PAGE_FLAGS(rack->debug_flags));
 			}
 			return FALSE; // Caller need not unlock
 		}
 	}
-	return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr)
+	return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(tiny_mag_ptr)
 }
 #endif // CONFIG_RECIRC_DEPOT
 
 static MALLOC_INLINE boolean_t
-small_free_no_lock(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, region_t region, void *ptr, msize_t msize)
+small_free_no_lock(rack_t *rack, magazine_t *small_mag_ptr, mag_index_t mag_index, region_t region, void *ptr, msize_t msize)
 {
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
 	unsigned index = SMALL_META_INDEX_FOR_PTR(ptr);
 	size_t original_size = SMALL_BYTES_FOR_MSIZE(msize);
-	unsigned char *next_block = ((unsigned char *)ptr + original_size);
+	void *next_block = ptr + original_size;
 	msize_t next_index = index + msize;
 
-	MALLOC_TRACE(TRACE_small_free, (uintptr_t)szone, (uintptr_t)small_mag_ptr, (uintptr_t)ptr, SMALL_BYTES_FOR_MSIZE(msize));
+	MALLOC_TRACE(TRACE_small_free, (uintptr_t)rack, (uintptr_t)small_mag_ptr, (uintptr_t)ptr, SMALL_BYTES_FOR_MSIZE(msize));
 
 #if CONFIG_AGGRESSIVE_MADVISE || CONFIG_RECIRC_DEPOT
 	void *original_ptr = ptr;
-#endif
+#endif // CONFIG_AGGRESSIVE_MADVISE || CONFIG_RECIRC_DEPOT
 
 #if DEBUG_MALLOC
 	if (LOG(szone, ptr)) {
-		malloc_printf("in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
+		malloc_report(ASL_LEVEL_ERR, "in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
 	}
 	if (!msize) {
-		szone_error(szone, 1, "trying to free small block that is too small", ptr, "in small_free_no_lock(), ptr=%p, msize=%d\n",
-					ptr, msize);
-	}
-#endif
+		malloc_zone_error(rack->debug_flags, true, "trying to free small block that is too small in small_free_no_lock(), ptr=%p, msize=%d\n",
+				ptr, msize);
+	}
+#endif
+
+	// Check that the region cookie is intact.
+	region_check_cookie(region, &REGION_COOKIE_FOR_SMALL_REGION(region));
 
 	// We try to coalesce this block with the preceeding one
 	if (index > 0 && (meta_headers[index - 1] & SMALL_IS_FREE)) {
 		msize_t previous_msize = meta_headers[index - 1] & ~SMALL_IS_FREE;
 		grain_t previous_index = index - previous_msize;
 
-		// Check if the metadata for the start of the region is also free.
+		// Check if the metadata for the start of the block is also free.
 		if (meta_headers[previous_index] == (previous_msize | SMALL_IS_FREE)) {
 			void *previous_ptr = (void *)((uintptr_t)ptr - SMALL_BYTES_FOR_MSIZE(previous_msize));
-			free_list_t previous = small_free_list_find_by_ptr(szone, small_mag_ptr, previous_ptr, previous_msize);
-			small_free_list_remove_ptr(szone, small_mag_ptr, previous, previous_msize);
+			free_list_t previous = small_free_list_find_by_ptr(rack, small_mag_ptr, previous_ptr, previous_msize);
+			small_free_list_remove_ptr(rack, small_mag_ptr, previous, previous_msize);
 			ptr = previous_ptr;
+			small_meta_header_set_middle(meta_headers, index); // This block is now a middle block.
 			msize += previous_msize;
 			index -= previous_msize;
 		} else {
@@ -1104,49 +1375,50 @@
 	}
 
 	// Try to coalesce with this block with the next block
-	if ((next_block < SMALL_REGION_END(region)) && (meta_headers[next_index] & SMALL_IS_FREE)) {
+	if ((next_block < SMALL_REGION_HEAP_END(region)) && (meta_headers[next_index] & SMALL_IS_FREE)) {
 		msize_t next_msize = meta_headers[next_index] & ~SMALL_IS_FREE;
-		free_list_t next = small_free_list_find_by_ptr(szone, small_mag_ptr, next_block, next_msize);
-		small_free_list_remove_ptr(szone, small_mag_ptr, next, next_msize);
+		free_list_t next = small_free_list_find_by_ptr(rack, small_mag_ptr, next_block, next_msize);
+		small_free_list_remove_ptr(rack, small_mag_ptr, next, next_msize);
 		msize += next_msize;
 	}
 
-	if (szone->debug_flags & MALLOC_DO_SCRIBBLE) {
+	if (rack->debug_flags & MALLOC_DO_SCRIBBLE) {
 		if (!msize) {
-			szone_error(szone, 1, "incorrect size information - block header was damaged", ptr, NULL);
+			malloc_zone_error(rack->debug_flags, true, "incorrect size information for %p - block header was damaged\n", ptr);
 		} else {
 			memset(ptr, SCRABBLE_BYTE, SMALL_BYTES_FOR_MSIZE(msize));
 		}
 	}
 
-	free_list_t freee = small_free_list_add_ptr(szone, small_mag_ptr, ptr, msize);
+	free_list_t freee = small_free_list_add_ptr(rack, small_mag_ptr, ptr, msize);
 
 	// use original_size and not msize to avoid double counting the coalesced blocks
 	small_mag_ptr->mag_num_bytes_in_objects -= original_size;
-	small_mag_ptr->mag_num_objects--;
 
 	// Update this region's bytes in use count
-	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(region);
-	size_t bytes_used = node->bytes_used - original_size;
-	node->bytes_used = (unsigned int)bytes_used;
+	region_trailer_t *trailer = REGION_TRAILER_FOR_SMALL_REGION(region);
+	size_t bytes_used = trailer->bytes_used - original_size;
+	trailer->bytes_used = (unsigned int)bytes_used;
 
 #if CONFIG_AGGRESSIVE_MADVISE
-	small_madvise_free_range_no_lock(szone, small_mag_ptr, region, freee, msize, original_ptr, original_size);
-#endif
-
-	// Caller must do SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr) if this function
+	if (aggressive_madvise_enabled) {
+		small_madvise_free_range_no_lock(rack, small_mag_ptr, region, freee, msize, original_ptr, original_size);
+	}
+#endif
+
+	// Caller must do SZONE_MAGAZINE_PTR_UNLOCK(tiny_mag_ptr) if this function
 	// returns TRUE.
 	boolean_t needs_unlock = TRUE;
 
 #if CONFIG_RECIRC_DEPOT
-	needs_unlock = small_free_try_recirc_to_depot(szone, small_mag_ptr, mag_index, region, freee, msize, original_ptr, original_size);
-#endif
+	needs_unlock = small_free_try_recirc_to_depot(rack, small_mag_ptr, mag_index, region, freee, msize, original_ptr, original_size);
+#endif // CONFIG_RECIRC_DEPOT
 	return needs_unlock;
 }
 
 // Allocates from the last region or a freshly allocated region
 static void *
-small_malloc_from_region_no_lock(szone_t *szone,
+small_malloc_from_region_no_lock(rack_t *rack,
 								 magazine_t *small_mag_ptr,
 								 mag_index_t mag_index,
 								 msize_t msize,
@@ -1157,55 +1429,22 @@
 	// Before anything we transform the mag_bytes_free_at_end or mag_bytes_free_at_start - if any - to a regular free block
 	/* FIXME: last_block needs to be coalesced with previous entry if free, <rdar://5462322> */
 	if (small_mag_ptr->mag_bytes_free_at_end || small_mag_ptr->mag_bytes_free_at_start) {
-		small_finalize_region(szone, small_mag_ptr);
-	}
-
-	// Here find the only place in smallville that (infrequently) takes the small_regions_lock.
-	// Only one thread at a time should be permitted to assess the density of the hash
-	// ring and adjust if needed.
-	// Only one thread at a time should be permitted to insert its new region on
-	// the hash ring.
-	// It is safe for all other threads to read the hash ring (hashed_regions) and
-	// the associated sizes (num_regions_allocated and num_small_regions).
-
-	_malloc_lock_lock(&szone->small_regions_lock);
-	// Check to see if the hash ring of small regions needs to grow.  Try to
-	// avoid the hash ring becoming too dense.
-	if (szone->small_region_generation->num_regions_allocated < (2 * szone->num_small_regions)) {
-		region_t *new_regions;
-		size_t new_size;
-		size_t new_shift = szone->small_region_generation->num_regions_allocated_shift; // In/Out parameter
-		new_regions = hash_regions_grow_no_lock(szone, szone->small_region_generation->hashed_regions,
-												szone->small_region_generation->num_regions_allocated, &new_shift, &new_size);
-		// Do not deallocate the current hashed_regions allocation since someone
-		// may be iterating it.  Instead, just leak it.
-
-		// Prepare to advance to the "next generation" of the hash ring.
-		szone->small_region_generation->nextgen->hashed_regions = new_regions;
-		szone->small_region_generation->nextgen->num_regions_allocated = new_size;
-		szone->small_region_generation->nextgen->num_regions_allocated_shift = new_shift;
-
-		// Throw the switch to atomically advance to the next generation.
-		szone->small_region_generation = szone->small_region_generation->nextgen;
-		// Ensure everyone sees the advance.
-		OSMemoryBarrier();
-	}
+		small_finalize_region(rack, small_mag_ptr);
+	}
+
+	small_region_t region = (small_region_t)aligned_address;
+
 	// Tag the region at "aligned_address" as belonging to us,
 	// and so put it under the protection of the magazine lock we are holding.
 	// Do this before advertising "aligned_address" on the hash ring(!)
-	MAGAZINE_INDEX_FOR_SMALL_REGION(aligned_address) = mag_index;
-
-	// Insert the new region into the hash ring, and update malloc statistics
-	hash_region_insert_no_lock(szone->small_region_generation->hashed_regions,
-							   szone->small_region_generation->num_regions_allocated, szone->small_region_generation->num_regions_allocated_shift,
-							   aligned_address);
-
-	szone->num_small_regions++;
-
-	_malloc_lock_unlock(&szone->small_regions_lock);
-
-	small_mag_ptr->mag_last_region = aligned_address;
-	BYTES_USED_FOR_SMALL_REGION(aligned_address) = SMALL_BYTES_FOR_MSIZE(msize);
+	MAGAZINE_INDEX_FOR_SMALL_REGION(region) = mag_index;
+
+	// Insert the new region into the hash ring
+	rack_region_insert(rack, region);
+
+	small_mag_ptr->mag_last_region = region;
+	BYTES_USED_FOR_SMALL_REGION(region) = SMALL_BYTES_FOR_MSIZE(msize);
+
 #if CONFIG_ASLR_INTERNAL
 	int offset_msize = malloc_entropy[1] & SMALL_ENTROPY_MASK;
 #if DEBUG_MALLOC
@@ -1213,17 +1452,17 @@
 		offset_msize = strtol(getenv("MallocASLRForce"), NULL, 0) & SMALL_ENTROPY_MASK;
 	}
 	if (getenv("MallocASLRPrint")) {
-		malloc_printf("Region: %p offset: %d\n", aligned_address, offset_msize);
+		malloc_report(ASL_LEVEL_INFO, "Region: %p offset: %d\n", region, offset_msize);
 	}
 #endif
 #else
 	int offset_msize = 0;
 #endif
-	ptr = (void *)((uintptr_t)aligned_address + SMALL_BYTES_FOR_MSIZE(offset_msize));
+	ptr = (void *)(SMALL_REGION_HEAP_BASE(region) + SMALL_BYTES_FOR_MSIZE(offset_msize));
 	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), offset_msize, msize);
 	small_mag_ptr->mag_num_objects++;
 	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(msize);
-	small_mag_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
+	small_mag_ptr->num_bytes_in_magazine += SMALL_HEAP_SIZE;
 
 	// add a big free block at the end
 	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), offset_msize + msize, NUM_SMALL_BLOCKS - msize - offset_msize);
@@ -1240,7 +1479,7 @@
 #endif
 
 	// connect to magazine as last node
-	recirc_list_splice_last(szone, small_mag_ptr, REGION_TRAILER_FOR_SMALL_REGION(aligned_address));
+	recirc_list_splice_last(rack, small_mag_ptr, REGION_TRAILER_FOR_SMALL_REGION(region));
 
 	return ptr;
 }
@@ -1248,14 +1487,8 @@
 void *
 small_memalign(szone_t *szone, size_t alignment, size_t size, size_t span)
 {
-	if (size <= SMALL_THRESHOLD) {
-		// ensure block allocated by small does not have a tiny-possible size
-		size = SMALL_THRESHOLD + TINY_QUANTUM;
-		span = size + alignment - 1;
-	}
-
 	msize_t mspan = SMALL_MSIZE_FOR_BYTES(span + SMALL_QUANTUM - 1);
-	void *p = szone_malloc(szone, span); // avoid inlining small_malloc_should_clear(szone, mspan, 0);
+	void *p = small_malloc_should_clear(&szone->small_rack, mspan, 0);
 
 	if (NULL == p) {
 		return NULL;
@@ -1272,65 +1505,71 @@
 		void *q = (void *)(((uintptr_t)p) + pad);
 
 		// Mark q as block header and in-use, thus creating two blocks.
-		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
-																	 REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
-																	 MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
+		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone->small_rack.magazines,
+				REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
+				MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(p), SMALL_META_INDEX_FOR_PTR(p), mpad);
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), msize + mwaste);
 		small_mag_ptr->mag_num_objects++;
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 
 		// Give up mpad blocks beginning at p to the small free list
-		// region_t r = SMALL_REGION_FOR_PTR(p);
-		szone_free(szone, p); // avoid inlining free_small(szone, p, &r);
+		free_small(&szone->small_rack, p, SMALL_REGION_FOR_PTR(p), SMALL_BYTES_FOR_MSIZE(mpad));
 
 		p = q; // advance p to the desired alignment
 	}
 	if (mwaste > 0) {
 		void *q = (void *)(((uintptr_t)p) + SMALL_BYTES_FOR_MSIZE(msize));
 		// Mark q as block header and in-use, thus creating two blocks.
-		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
-																	 REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
-																	 MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
+		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone->small_rack.magazines,
+				REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
+				MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(p), SMALL_META_INDEX_FOR_PTR(p), msize);
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), mwaste);
 		small_mag_ptr->mag_num_objects++;
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 
 		// Give up mwaste blocks beginning at q to the small free list
-		// region_t r = SMALL_REGION_FOR_PTR(q);
-		szone_free(szone, q); // avoid inlining free_small(szone, q, &r);
+		free_small(&szone->small_rack, q, SMALL_REGION_FOR_PTR(q), SMALL_BYTES_FOR_MSIZE(mwaste));
 	}
 
 	return p; // p has the desired size and alignment, and can later be free()'d
 }
 
+boolean_t
+small_claimed_address(rack_t *rack, void *ptr)
+{
+	region_t r = small_region_for_ptr_no_lock(rack, ptr);
+	return r && ptr >= SMALL_REGION_HEAP_BASE(r)
+			&& ptr < SMALL_REGION_HEAP_END(r);
+}
+
 void *
-small_try_shrink_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_good_size)
+small_try_shrink_in_place(rack_t *rack, void *ptr, size_t old_size, size_t new_good_size)
 {
 	msize_t new_msize = SMALL_MSIZE_FOR_BYTES(new_good_size);
 	msize_t mshrinkage = SMALL_MSIZE_FOR_BYTES(old_size) - new_msize;
 
 	if (mshrinkage) {
 		void *q = (void *)((uintptr_t)ptr + SMALL_BYTES_FOR_MSIZE(new_msize));
-		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
-																	 REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)),
-																	 MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));
+		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(rack->magazines,
+				REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)),
+				MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));
 
 		// Mark q as block header and in-use, thus creating two blocks.
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), SMALL_META_INDEX_FOR_PTR(ptr), new_msize);
 		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), mshrinkage);
 		small_mag_ptr->mag_num_objects++;
 
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-		szone_free(szone, q); // avoid inlining free_small(szone, q, ...);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+		free_small(rack, q, SMALL_REGION_FOR_PTR(q), 0);
 	}
 
 	return ptr;
 }
 
 boolean_t
-small_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
+small_try_realloc_in_place(rack_t *rack, void *ptr, size_t old_size, size_t new_size)
 {
 	// returns 1 on success
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
@@ -1355,58 +1594,105 @@
 
 #if DEBUG_MALLOC
 	if ((uintptr_t)next_block & (SMALL_QUANTUM - 1)) {
-		szone_error(szone, 1, "internal invariant broken in realloc(next_block)", next_block, NULL);
+		malloc_zone_error(rack->debug_flags, true, "internal invariant broken in realloc(next_block) for %p\n", next_block);
 	}
 	if (meta_headers[index] != old_msize) {
-		malloc_printf("*** small_try_realloc_in_place incorrect old %d %d\n", meta_headers[index], old_msize);
-	}
-#endif
-
-	magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
-																 REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)), MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));
+		malloc_report(ASL_LEVEL_ERR, "*** small_try_realloc_in_place incorrect old %d %d\n", meta_headers[index], old_msize);
+	}
+#endif
+
+	magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(rack->magazines,
+			REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)),
+			MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));
 	if (DEPOT_MAGAZINE_INDEX == MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr))) {
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 		return 0;
 	}
 
-	/*
-	 * Look for a free block immediately afterwards.  If it's large enough, we can consume (part of)
-	 * it.
-	 */
-	next_msize_and_free = meta_headers[next_index];
-	is_free = next_msize_and_free & SMALL_IS_FREE;
-	if (!is_free) {
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-		return 0; // next_block is in use;
-	}
-
-	next_msize = next_msize_and_free & ~SMALL_IS_FREE;
-	if (old_msize + next_msize < new_msize) {
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-		return 0; // even with next block, not enough
-	}
-
-	// The following block is big enough; pull it from its freelist and chop off enough to satisfy
-	// our needs.
-	free_list_t freee = small_free_list_find_by_ptr(szone, small_mag_ptr, next_block, next_msize);
-	small_free_list_remove_ptr(szone, small_mag_ptr, freee, next_msize);
-	small_meta_header_set_middle(meta_headers, next_index);
-	leftover_msize = old_msize + next_msize - new_msize;
-	if (leftover_msize) {
-		/* there's some left, so put the remainder back */
-		leftover = (unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(new_msize);
-
-		small_free_list_add_ptr(szone, small_mag_ptr, leftover, leftover_msize);
-	}
+	msize_t coalesced_msize = new_msize - old_msize;
+#if CONFIG_SMALL_CACHE
+	void *last_free_ptr = small_mag_ptr->mag_last_free;
+	msize_t last_free_msize = small_mag_ptr->mag_last_free_msize;
+	if (last_free_ptr == next_block && old_msize + last_free_msize >= new_msize) {
+		/*
+		 * There is a block in mag_last_free and it's immediately after
+		 * this block and it's large enough. We can use some or all of it.
+		 */
+		leftover_msize = last_free_msize - coalesced_msize;
+		if (leftover_msize) {
+			small_mag_ptr->mag_last_free_msize -= coalesced_msize;
+			small_mag_ptr->mag_last_free += new_size - old_size;
+			// The block in mag_last_free is still marked as header and in-use, so copy that
+			// state to the block that remains. The state for the block that we're going to
+			// use is adjusted by the small_meta_header_set_middle() call below.
+			small_meta_header_set_in_use(meta_headers, index + new_msize, leftover_msize);
+		} else {
+			// Using the whole block.
+			small_mag_ptr->mag_last_free = NULL;
+			small_mag_ptr->mag_last_free_msize = 0;
+			small_mag_ptr->mag_last_free_rgn = NULL;
+		}
+		small_meta_header_set_in_use(meta_headers, index, new_msize);
+		small_meta_header_set_middle(meta_headers, next_index);
+	} else {
+#endif // CONFIG_SMALL_CACHE
+		/*
+		 * Try to expand into unused space immediately after this block.
+		 */
+		msize_t unused_msize = SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end);
+		void *unused_start = SMALL_REGION_HEAP_END(SMALL_REGION_FOR_PTR(ptr)) - small_mag_ptr->mag_bytes_free_at_end;
+		if (small_mag_ptr->mag_last_region == SMALL_REGION_FOR_PTR(ptr)
+				&& coalesced_msize < unused_msize && unused_start == ptr + old_size) {
+			// Extend the in-use for this block to the new size
+			small_meta_header_set_in_use(meta_headers, index, new_msize);
+
+			// Clear the in-use size for the start of the area we extended into
+			small_meta_header_set_middle(meta_headers, next_index);
+
+			// Reduce mag_bytes_free_at_end and update its in-use size.
+			small_mag_ptr->mag_bytes_free_at_end -= SMALL_BYTES_FOR_MSIZE(coalesced_msize);
+			small_meta_header_set_in_use(meta_headers, index + new_msize, SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end));
+		} else {
+			/*
+			 * Look for a free block immediately afterwards.  If it's large enough, we can consume (part of)
+			 * it.
+			 */
+			next_msize_and_free = meta_headers[next_index];
+			is_free = next_msize_and_free & SMALL_IS_FREE;
+			if (!is_free) {
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+				return 0; // next_block is in use;
+			}
+
+			next_msize = next_msize_and_free & ~SMALL_IS_FREE;
+			if (old_msize + next_msize < new_msize) {
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+				return 0; // even with next block, not enough
+			}
+
+			// The following block is big enough; pull it from its freelist and chop off enough to satisfy
+			// our needs.
+			free_list_t freee = small_free_list_find_by_ptr(rack, small_mag_ptr, next_block, next_msize);
+			small_free_list_remove_ptr(rack, small_mag_ptr, freee, next_msize);
+			small_meta_header_set_middle(meta_headers, next_index);
+			leftover_msize = old_msize + next_msize - new_msize;
+			if (leftover_msize) {
+				/* there's some left, so put the remainder back */
+				leftover = (unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(new_msize);
+				small_free_list_add_ptr(rack, small_mag_ptr, leftover, leftover_msize);
+			}
+			small_meta_header_set_in_use(meta_headers, index, new_msize);
+		}
+#if CONFIG_SMALL_CACHE
+	}
+#endif // CONFIG_SMALL_CACHE
 #if DEBUG_MALLOC
 	if (SMALL_BYTES_FOR_MSIZE(new_msize) > szone->large_threshold) {
-		malloc_printf("*** realloc in place for %p exceeded msize=%d\n", new_msize);
-	}
-#endif
-	small_meta_header_set_in_use(meta_headers, index, new_msize);
-#if DEBUG_MALLOC
+		malloc_report(ASL_LEVEL_ERR, "*** realloc in place for %p exceeded msize=%d\n", new_msize);
+	}
+
 	if (LOG(szone, ptr)) {
-		malloc_printf("in small_try_realloc_in_place(), ptr=%p, msize=%d\n", ptr, *SMALL_METADATA_FOR_PTR(ptr));
+		malloc_report(ASL_LEVEL_INFO, "in small_try_realloc_in_place(), ptr=%p, msize=%d\n", ptr, *SMALL_METADATA_FOR_PTR(ptr));
 	}
 #endif
 	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(new_msize - old_msize);
@@ -1417,7 +1703,7 @@
 	node->bytes_used = (unsigned int)bytes_used;
 
 	// Emptiness discriminant
-	if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
+	if (bytes_used < DENSITY_THRESHOLD(SMALL_HEAP_SIZE)) {
 		/* After this reallocation the region is still sparse, so it must have been even more so before
 		 * the reallocation. That implies the region is already correctly marked. Do nothing. */
 	} else {
@@ -1426,17 +1712,24 @@
 		node->recirc_suitable = FALSE;
 	}
 
-	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+	SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 	CHECK(szone, __PRETTY_FUNCTION__);
 	return 1;
 }
 
+static char *small_check_fail_msg = "check: incorrect small region ";
+
+#define SMALL_CHECK_FAIL(fmt, ...) \
+	malloc_zone_check_fail(small_check_fail_msg, \
+			"%ld, counter=%d\n" fmt,  region_index, counter, __VA_ARGS__);
+
 boolean_t
-small_check_region(szone_t *szone, region_t region)
-{
-	unsigned char *ptr = SMALL_REGION_ADDRESS(region);
+small_check_region(rack_t *rack, region_t region, size_t region_index,
+		unsigned counter)
+{
+	unsigned char *ptr = SMALL_REGION_HEAP_BASE(region);
 	msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
-	unsigned char *region_end = SMALL_REGION_END(region);
+	unsigned char *region_end = SMALL_REGION_HEAP_END(region);
 	msize_t prev_free = 0;
 	unsigned index;
 	msize_t msize_and_free;
@@ -1444,7 +1737,7 @@
 	free_list_t free_head, previous, next;
 	msize_t *follower;
 	mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
-	magazine_t *small_mag_ptr = &(szone->small_magazines[mag_index]);
+	magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
 
 	// Assumes locked
 	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);
@@ -1461,13 +1754,13 @@
 			// block is in use
 			msize = msize_and_free;
 			if (!msize) {
-				malloc_printf("*** invariant broken: null msize ptr=%p num_small_regions=%d end=%p\n", ptr,
-							  szone->num_small_regions, region_end);
+				SMALL_CHECK_FAIL("*** invariant broken: null msize ptr=%p num_small_regions=%d end=%p\n", ptr,
+							  (int)rack->num_regions, region_end);
 				return 0;
 			}
 #if !CONFIG_RELAXED_INVARIANT_CHECKS
 			if (SMALL_BYTES_FOR_MSIZE(msize) > szone->large_threshold) {
-				malloc_printf("*** invariant broken for %p this small msize=%d - size is too large\n", ptr, msize_and_free);
+				SMALL_CHECK_FAIL("*** invariant broken for %p this small msize=%d - size is too large\n", ptr, msize_and_free);
 				return 0;
 			}
 #endif // CONFIG_RELAXED_INVARIANT_CHECKS
@@ -1479,12 +1772,12 @@
 			free_head = (free_list_t){ .p = ptr };
 			follower = (msize_t *)FOLLOWING_SMALL_PTR(ptr, msize);
 			if (!msize) {
-				malloc_printf("*** invariant broken for free block %p this msize=%d\n", ptr, msize);
+				SMALL_CHECK_FAIL("*** invariant broken for free block %p this msize=%d\n", ptr, msize);
 				return 0;
 			}
 #if !CONFIG_RELAXED_INVARIANT_CHECKS
 			if (prev_free) {
-				malloc_printf("*** invariant broken for %p (2 free in a row)\n", ptr);
+				SMALL_CHECK_FAIL("*** invariant broken for %p (2 free in a row)\n", ptr);
 				return 0;
 			}
 #endif
@@ -1497,21 +1790,20 @@
 				}
 			}
 
-			previous = small_free_list_get_previous(szone, free_head);
-			next = small_free_list_get_next(szone, free_head);
-			if (previous.p && !SMALL_PTR_IS_FREE(small_free_list_get_ptr(szone, previous))) {
-				malloc_printf("*** invariant broken for %p (previous %p is not a free pointer)\n", ptr, small_free_list_get_ptr(szone, previous));
+			previous = small_free_list_get_previous(rack, free_head);
+			next = small_free_list_get_next(rack, free_head);
+			if (previous.p && !SMALL_PTR_IS_FREE(small_free_list_get_ptr(previous))) {
+				SMALL_CHECK_FAIL("*** invariant broken for %p (previous %p is not a free pointer)\n", ptr, small_free_list_get_ptr(previous));
 				return 0;
 			}
-			if (next.p && !SMALL_PTR_IS_FREE(small_free_list_get_ptr(szone, next))) {
-				malloc_printf("*** invariant broken for %p (next %p is not a free pointer)\n", ptr, small_free_list_get_ptr(szone, next));
+			if (next.p && !SMALL_PTR_IS_FREE(small_free_list_get_ptr(next))) {
+				SMALL_CHECK_FAIL("*** invariant broken for %p (next %p is not a free pointer)\n", ptr, small_free_list_get_ptr(next));
 				return 0;
 			}
 			if (SMALL_PREVIOUS_MSIZE(follower) != msize) {
-				malloc_printf(
-							  "*** invariant broken for small free %p followed by %p in region [%p-%p] "
-							  "(end marker incorrect) should be %d; in fact %d\n",
-							  ptr, follower, SMALL_REGION_ADDRESS(region), region_end, msize, SMALL_PREVIOUS_MSIZE(follower));
+				SMALL_CHECK_FAIL("*** invariant broken for small free %p followed by %p in region [%p-%p] "
+						"(end marker incorrect) should be %d; in fact %d\n",
+						ptr, follower, SMALL_REGION_HEAP_BASE(region), region_end, msize, SMALL_PREVIOUS_MSIZE(follower));
 				return 0;
 			}
 			ptr = (unsigned char *)follower;
@@ -1548,7 +1840,7 @@
 	magazine_t *small_mag_base = NULL;
 
 	region_hash_generation_t *srg_ptr;
-	err = reader(task, (vm_address_t)szone->small_region_generation, sizeof(region_hash_generation_t), (void **)&srg_ptr);
+	err = reader(task, (vm_address_t)szone->small_rack.region_generation, sizeof(region_hash_generation_t), (void **)&srg_ptr);
 	if (err) {
 		return err;
 	}
@@ -1561,7 +1853,7 @@
 
 	if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
 		// Map in all active magazines. Do this outside the iteration over regions.
-		err = reader(task, (vm_address_t)(szone->small_magazines), szone->num_small_magazines * sizeof(magazine_t),
+		err = reader(task, (vm_address_t)(szone->small_rack.magazines), szone->small_rack.num_magazines * sizeof(magazine_t),
 					 (void **)&small_mag_base);
 		if (err) {
 			return err;
@@ -1571,24 +1863,20 @@
 	for (index = 0; index < num_regions; ++index) {
 		region = regions[index];
 		if (HASHRING_OPEN_ENTRY != region && HASHRING_REGION_DEALLOCATED != region) {
-			range.address = (vm_address_t)SMALL_REGION_ADDRESS(region);
-			range.size = SMALL_REGION_SIZE;
+			range.address = (vm_address_t)SMALL_REGION_HEAP_BASE(region);
+			range.size = SMALL_HEAP_SIZE;
 			if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
-				admin_range.address = range.address + SMALL_METADATA_START;
+				admin_range.address = SMALL_REGION_METADATA(region);
 				admin_range.size = SMALL_METADATA_SIZE;
 				recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &admin_range, 1);
 			}
 			if (type_mask & (MALLOC_PTR_REGION_RANGE_TYPE | MALLOC_ADMIN_REGION_RANGE_TYPE)) {
 				ptr_range.address = range.address;
-				ptr_range.size = NUM_SMALL_BLOCKS * SMALL_QUANTUM;
+				ptr_range.size = SMALL_HEAP_SIZE;
 				recorder(task, context, MALLOC_PTR_REGION_RANGE_TYPE, &ptr_range, 1);
 			}
 			if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
-				void *mag_last_free;
-				vm_address_t mag_last_free_ptr = 0;
-				msize_t mag_last_free_msize = 0;
-
-				err = reader(task, range.address, range.size, (void **)&mapped_region);
+				err = reader(task, (vm_address_t)region, (vm_size_t)SMALL_REGION_SIZE, (void **)&mapped_region);
 				if (err) {
 					return err;
 				}
@@ -1596,38 +1884,53 @@
 				mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(mapped_region);
 				magazine_t *small_mag_ptr = small_mag_base + mag_index;
 
-				if (DEPOT_MAGAZINE_INDEX != mag_index) {
-					mag_last_free = small_mag_ptr->mag_last_free;
-					if (mag_last_free) {
-						mag_last_free_ptr = (uintptr_t)mag_last_free & ~(SMALL_QUANTUM - 1);
-						mag_last_free_msize = (uintptr_t)mag_last_free & (SMALL_QUANTUM - 1);
-					}
-				} else {
-					for (mag_index = 0; mag_index < szone->num_small_magazines; mag_index++) {
-						if ((void *)range.address == (small_mag_base + mag_index)->mag_last_free_rgn) {
-							mag_last_free = (small_mag_base + mag_index)->mag_last_free;
-							if (mag_last_free) {
-								mag_last_free_ptr = (uintptr_t)mag_last_free & ~(SMALL_QUANTUM - 1);
-								mag_last_free_msize = (uintptr_t)mag_last_free & (SMALL_QUANTUM - 1);
-							}
-						}
+				int cached_free_blocks = 0;
+#if CONFIG_SMALL_CACHE
+				// Each magazine could have a pointer to a cached free block from
+				// this region. Count the regions that have such a pointer.
+				for (mag_index = 0; mag_index < szone->small_rack.num_magazines; mag_index++) {
+					if (region == (small_mag_base + mag_index)->mag_last_free_rgn) {
+						cached_free_blocks++;
 					}
 				}
-
-				block_header = (msize_t *)(mapped_region + SMALL_METADATA_START + sizeof(region_trailer_t));
+#endif // CONFIG_SMALL_CACHE
+
+				block_header = SMALL_META_HEADER_FOR_REGION(mapped_region);
 				block_index = 0;
 				block_limit = NUM_SMALL_BLOCKS;
 				if (region == small_mag_ptr->mag_last_region) {
 					block_index += SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start);
 					block_limit -= SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end);
 				}
-				while (block_index < block_limit) {
+
+				for (;block_index < block_limit; block_index += msize) {
 					msize_and_free = block_header[block_index];
 					msize = msize_and_free & ~SMALL_IS_FREE;
-					if (!(msize_and_free & SMALL_IS_FREE) &&
-						range.address + SMALL_BYTES_FOR_MSIZE(block_index) != mag_last_free_ptr) {
+					if (!msize) {
+						return KERN_FAILURE; // Somethings amiss. Avoid looping at this block_index.
+					}
+					if (!(msize_and_free & SMALL_IS_FREE)) {
+						void *ptr = SMALL_REGION_HEAP_BASE(region) + SMALL_BYTES_FOR_MSIZE(block_index);
+#if CONFIG_SMALL_CACHE
+						// If there are still magazines that have cached free
+						// blocks in this region, check whether this is one of
+						// them and don't return the block pointer if it is.
+						boolean_t block_cached = false;
+						if (cached_free_blocks) {
+							for (mag_index = 0; mag_index < szone->small_rack.num_magazines; mag_index++) {
+								if (ptr == (small_mag_base + mag_index)->mag_last_free) {
+									block_cached = true;
+									cached_free_blocks--;
+									break;
+								}
+							}
+						}
+						if (block_cached) {
+							continue;
+						}
+#endif // CONFIG_SMALL_CACHE
 						// Block in use
-						buffer[count].address = range.address + SMALL_BYTES_FOR_MSIZE(block_index);
+						buffer[count].address = (vm_address_t)ptr;
 						buffer[count].size = SMALL_BYTES_FOR_MSIZE(msize);
 						count++;
 						if (count >= MAX_RECORDER_BUFFER) {
@@ -1635,11 +1938,6 @@
 							count = 0;
 						}
 					}
-
-					if (!msize) {
-						return KERN_FAILURE; // Somethings amiss. Avoid looping at this block_index.
-					}
-					block_index += msize;
 				}
 				if (count) {
 					recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
@@ -1652,10 +1950,10 @@
 }
 
 static void *
-small_malloc_from_free_list(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
+small_malloc_from_free_list(rack_t *rack, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
 {
 	msize_t this_msize;
-	grain_t slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
+	grain_t slot = SMALL_FREE_SLOT_FOR_MSIZE(rack, msize);
 	free_list_t *free_list = small_mag_ptr->mag_free_list;
 	free_list_t *the_slot = free_list + slot;
 	free_list_t *limit;
@@ -1668,64 +1966,56 @@
 	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);
 
 	// Look for an exact match by checking the freelist for this msize.
-	//
-	if (small_free_list_get_ptr(szone, *the_slot)) {
-		ptr = small_free_list_get_ptr(szone, *the_slot);
+	if (small_free_list_get_ptr(*the_slot)) {
+		ptr = small_free_list_get_ptr(*the_slot);
 		this_msize = msize;
-		small_free_list_remove_ptr(szone, small_mag_ptr, *the_slot, msize);
+		small_free_list_remove_ptr(rack, small_mag_ptr, *the_slot, msize);
 		goto return_small_alloc;
 	}
 
 	// Mask off the bits representing slots holding free blocks smaller than
 	// the size we need.  If there are no larger free blocks, try allocating
 	// from the free space at the end of the small region.
-	if (szone->is_largemem) {
-		// BITMAPN_CTZ implementation
-		unsigned idx = slot >> 5;
-		bitmap = 0;
-		unsigned mask = ~((1 << (slot & 31)) - 1);
-		for (; idx < SMALL_BITMAP_WORDS; ++idx) {
-			bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
-			if (bitmap != 0) {
-				break;
-			}
-			mask = ~0U;
-		}
-		// Check for fallthrough: No bits set in bitmap
-		if ((bitmap == 0) && (idx == SMALL_BITMAP_WORDS)) {
-			goto try_small_from_end;
-		}
-
-		// Start looking at the first set bit, plus 32 bits for every word of
-		// zeroes or entries that were too small.
-		slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
-	} else {
-		bitmap = small_mag_ptr->mag_bitmap[0] & ~((1 << slot) - 1);
-		if (!bitmap) {
-			goto try_small_from_end;
-		}
-
-		slot = BITMAP32_CTZ((&bitmap));
-	}
+	//
+	// BITMAPN_CTZ implementation
+	unsigned idx = slot >> 5;
+	bitmap = 0;
+	unsigned mask = ~((1 << (slot & 31)) - 1);
+	for (; idx < SMALL_FREELIST_BITMAP_WORDS(rack); ++idx) {
+		bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
+		if (bitmap != 0) {
+			break;
+		}
+		mask = ~0U;
+	}
+	// Check for fallthrough: No bits set in bitmap
+	if ((bitmap == 0) && (idx == SMALL_FREELIST_BITMAP_WORDS(rack))) {
+		goto try_small_from_end;
+	}
+
+	// Start looking at the first set bit, plus 32 bits for every word of
+	// zeroes or entries that were too small.
+	slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
+
 	// FIXME: Explain use of - 1 here, last slot has special meaning
-	limit = free_list + szone->num_small_slots - 1;
+	limit = free_list + SMALL_FREE_SLOT_COUNT(rack) - 1;
 	free_list += slot;
 
 	// Attempt to pull off the free_list slot that we now think is full.
-	if ((ptr = small_free_list_get_ptr(szone, *free_list))) {
+	if ((ptr = small_free_list_get_ptr(*free_list))) {
 		this_msize = SMALL_PTR_SIZE(ptr);
-		small_free_list_remove_ptr(szone, small_mag_ptr, *free_list, this_msize);
+		small_free_list_remove_ptr(rack, small_mag_ptr, *free_list, this_msize);
 		goto add_leftover_and_proceed;
 	}
 
 #if DEBUG_MALLOC
-	malloc_printf("in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n", slot);
+	malloc_report(ASL_LEVEL_ERR, "in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n", slot);
 #endif
 
 try_small_from_end:
 	// Let's see if we can use small_mag_ptr->mag_bytes_free_at_end
 	if (small_mag_ptr->mag_bytes_free_at_end >= SMALL_BYTES_FOR_MSIZE(msize)) {
-		ptr = SMALL_REGION_END(small_mag_ptr->mag_last_region) - small_mag_ptr->mag_bytes_free_at_end;
+		ptr = SMALL_REGION_HEAP_END(small_mag_ptr->mag_last_region) - small_mag_ptr->mag_bytes_free_at_end;
 		small_mag_ptr->mag_bytes_free_at_end -= SMALL_BYTES_FOR_MSIZE(msize);
 		if (small_mag_ptr->mag_bytes_free_at_end) {
 			// let's mark this block as in use to serve as boundary
@@ -1739,13 +2029,13 @@
 #if CONFIG_ASLR_INTERNAL
 	// Try from start if nothing left at end
 	if (small_mag_ptr->mag_bytes_free_at_start >= SMALL_BYTES_FOR_MSIZE(msize)) {
-		ptr = SMALL_REGION_ADDRESS(small_mag_ptr->mag_last_region) + small_mag_ptr->mag_bytes_free_at_start -
+		ptr = SMALL_REGION_HEAP_BASE(small_mag_ptr->mag_last_region) + small_mag_ptr->mag_bytes_free_at_start -
 				SMALL_BYTES_FOR_MSIZE(msize);
 		small_mag_ptr->mag_bytes_free_at_start -= SMALL_BYTES_FOR_MSIZE(msize);
 		if (small_mag_ptr->mag_bytes_free_at_start) {
 			// let's mark this block as in use to serve as boundary
-			small_meta_header_set_in_use(
-										 SMALL_META_HEADER_FOR_PTR(ptr), 0, SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start));
+			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), 0,
+					SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start));
 		}
 		this_msize = msize;
 		goto return_small_alloc;
@@ -1759,10 +2049,10 @@
 		leftover_ptr = (unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize);
 #if DEBUG_MALLOC
 		if (LOG(szone, ptr)) {
-			malloc_printf("in small_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
-		}
-#endif
-		small_free_list_add_ptr(szone, small_mag_ptr, leftover_ptr, leftover_msize);
+			malloc_report(ASL_LEVEL_INFO, "in small_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
+		}
+#endif
+		small_free_list_add_ptr(rack, small_mag_ptr, leftover_ptr, leftover_msize);
 		this_msize = msize;
 	}
 
@@ -1770,23 +2060,26 @@
 	small_mag_ptr->mag_num_objects++;
 	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(this_msize);
 
-	// Update this region's bytes in use count
-	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
-	size_t bytes_used = node->bytes_used + SMALL_BYTES_FOR_MSIZE(this_msize);
-	node->bytes_used = (unsigned int)bytes_used;
+	// Check that the region cookie is intact and update the region's bytes in use count
+	small_region_t region = SMALL_REGION_FOR_PTR(ptr);
+	region_check_cookie(region, &REGION_COOKIE_FOR_SMALL_REGION(region));
+
+	region_trailer_t *trailer = REGION_TRAILER_FOR_SMALL_REGION(region);
+	size_t bytes_used = trailer->bytes_used + SMALL_BYTES_FOR_MSIZE(this_msize);
+	trailer->bytes_used = (unsigned int)bytes_used;
 
 	// Emptiness discriminant
-	if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
+	if (bytes_used < DENSITY_THRESHOLD(SMALL_HEAP_SIZE)) {
 		/* After this allocation the region is still sparse, so it must have been even more so before
 		 * the allocation. That implies the region is already correctly marked. Do nothing. */
 	} else {
 		/* Region has crossed threshold from sparsity to density. Mark in not "suitable" on the
 		 * recirculation candidates list. */
-		node->recirc_suitable = FALSE;
+		trailer->recirc_suitable = FALSE;
 	}
 #if DEBUG_MALLOC
 	if (LOG(szone, ptr)) {
-		malloc_printf("in small_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
+		malloc_report(ASL_LEVEL_INFO, "in small_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
 	}
 #endif
 	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), SMALL_META_INDEX_FOR_PTR(ptr), this_msize);
@@ -1794,26 +2087,26 @@
 }
 
 void *
-small_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested)
+small_malloc_should_clear(rack_t *rack, msize_t msize, boolean_t cleared_requested)
 {
 	void *ptr;
-	mag_index_t mag_index = mag_get_thread_index(szone);
-	magazine_t *small_mag_ptr = &(szone->small_magazines[mag_index]);
-
-	MALLOC_TRACE(TRACE_small_malloc, (uintptr_t)szone, SMALL_BYTES_FOR_MSIZE(msize), (uintptr_t)small_mag_ptr, cleared_requested);
-
-	SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
+	mag_index_t mag_index = small_mag_get_thread_index() % rack->num_magazines;
+	magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
+
+	MALLOC_TRACE(TRACE_small_malloc, (uintptr_t)rack, SMALL_BYTES_FOR_MSIZE(msize), (uintptr_t)small_mag_ptr, cleared_requested);
+
+	SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
 
 #if CONFIG_SMALL_CACHE
-	ptr = (void *)small_mag_ptr->mag_last_free;
-
-	if ((((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) == msize) {
+	ptr = small_mag_ptr->mag_last_free;
+
+	if (small_mag_ptr->mag_last_free_msize == msize) {
 		// we have a winner
 		small_mag_ptr->mag_last_free = NULL;
+		small_mag_ptr->mag_last_free_msize = 0;
 		small_mag_ptr->mag_last_free_rgn = NULL;
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 		CHECK(szone, __PRETTY_FUNCTION__);
-		ptr = (void *)((uintptr_t)ptr & ~(SMALL_QUANTUM - 1));
 		if (cleared_requested) {
 			memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
 		}
@@ -1822,9 +2115,9 @@
 #endif /* CONFIG_SMALL_CACHE */
 
 	while (1) {
-		ptr = small_malloc_from_free_list(szone, small_mag_ptr, mag_index, msize);
+		ptr = small_malloc_from_free_list(rack, small_mag_ptr, mag_index, msize);
 		if (ptr) {
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 			CHECK(szone, __PRETTY_FUNCTION__);
 			if (cleared_requested) {
 				memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
@@ -1832,10 +2125,11 @@
 			return ptr;
 		}
 
-		if (small_get_region_from_depot(szone, small_mag_ptr, mag_index, msize)) {
-			ptr = small_malloc_from_free_list(szone, small_mag_ptr, mag_index, msize);
+#if CONFIG_RECIRC_DEPOT
+		if (small_get_region_from_depot(rack, small_mag_ptr, mag_index, msize)) {
+			ptr = small_malloc_from_free_list(rack, small_mag_ptr, mag_index, msize);
 			if (ptr) {
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				CHECK(szone, __PRETTY_FUNCTION__);
 				if (cleared_requested) {
 					memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
@@ -1843,6 +2137,7 @@
 				return ptr;
 			}
 		}
+#endif // CONFIG_RECIRC_DEPOT
 
 		// The magazine is exhausted. A new region (heap) must be allocated to satisfy this call to malloc().
 		// The allocation, an mmap() system call, will be performed outside the magazine spin locks by the first
@@ -1856,51 +2151,90 @@
 			// time to create a new region (do this outside the magazine lock)
 			small_mag_ptr->alloc_underway = TRUE;
 			OSMemoryBarrier();
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-			fresh_region = allocate_pages_securely(szone, SMALL_REGION_SIZE, SMALL_BLOCKS_ALIGN, VM_MEMORY_MALLOC_SMALL);
-			SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
-
-			MAGMALLOC_ALLOCREGION((void *)szone, (int)mag_index, fresh_region, SMALL_REGION_SIZE); // DTrace USDT Probe
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+			fresh_region = mvm_allocate_pages(SMALL_REGION_SIZE,
+					SMALL_BLOCKS_ALIGN,
+					MALLOC_FIX_GUARD_PAGE_FLAGS(rack->debug_flags),
+					VM_MEMORY_MALLOC_SMALL);
+			SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
+
+			// DTrace USDT Probe
+			MAGMALLOC_ALLOCREGION(SMALL_SZONE_FROM_RACK(rack), (int)mag_index, fresh_region, SMALL_REGION_SIZE);
 
 			if (!fresh_region) { // out of memory!
 				small_mag_ptr->alloc_underway = FALSE;
 				OSMemoryBarrier();
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				return NULL;
 			}
 
-			ptr = small_malloc_from_region_no_lock(szone, small_mag_ptr, mag_index, msize, fresh_region);
+			region_set_cookie(&REGION_COOKIE_FOR_SMALL_REGION(fresh_region));
+			ptr = small_malloc_from_region_no_lock(rack, small_mag_ptr, mag_index, msize, fresh_region);
 
 			// we don't clear because this freshly allocated space is pristine
 			small_mag_ptr->alloc_underway = FALSE;
 			OSMemoryBarrier();
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 			CHECK(szone, __PRETTY_FUNCTION__);
 			return ptr;
 		} else {
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 			yield();
-			SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
 		}
 	}
 	/* NOTREACHED */
 }
 
+size_t
+small_size(rack_t *rack, const void *ptr)
+{
+	if (small_region_for_ptr_no_lock(rack, ptr)) {
+		if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS) {
+			return 0;
+		}
+		msize_t msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
+		if (msize_and_free & SMALL_IS_FREE) {
+			return 0;
+		}
+#if CONFIG_SMALL_CACHE
+		{
+			mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
+			if (DEPOT_MAGAZINE_INDEX != mag_index) {
+				magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
+
+				if (ptr == small_mag_ptr->mag_last_free) {
+					return 0;
+				}
+			} else {
+				for (mag_index = 0; mag_index < rack->num_magazines; mag_index++) {
+					magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
+
+					if (ptr == small_mag_ptr->mag_last_free) {
+						return 0;
+					}
+				}
+			}
+		}
+#endif
+		return SMALL_BYTES_FOR_MSIZE(msize_and_free);
+	}
+
+	return 0;
+}
+
 static MALLOC_NOINLINE void
-free_small_botch(szone_t *szone, void *ptr)
-{
-	mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
-	magazine_t *small_mag_ptr = &(szone->small_magazines[mag_index]);
-	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
-	szone_error(szone, 1, "double free", ptr, NULL);
+free_small_botch(rack_t *rack, void *ptr)
+{
+	malloc_zone_error(rack->debug_flags, true, "double free for ptr %p\n", ptr);
 }
 
 void
-free_small(szone_t *szone, void *ptr, region_t small_region, size_t known_size)
+free_small(rack_t *rack, void *ptr, region_t small_region, size_t known_size)
 {
 	msize_t msize;
 	mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
-	magazine_t *small_mag_ptr = &(szone->small_magazines[mag_index]);
+	magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
 
 	// ptr is known to be in small_region
 	if (known_size) {
@@ -1908,40 +2242,43 @@
 	} else {
 		msize = SMALL_PTR_SIZE(ptr);
 		if (SMALL_PTR_IS_FREE(ptr)) {
-			free_small_botch(szone, ptr);
+			free_small_botch(rack, ptr);
 			return;
 		}
 	}
 
-	SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
+	SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
 
 #if CONFIG_SMALL_CACHE
 	// Depot does not participate in CONFIG_SMALL_CACHE since it can't be directly malloc()'d
 	if (DEPOT_MAGAZINE_INDEX != mag_index) {
 		void *ptr2 = small_mag_ptr->mag_last_free; // Might be NULL
+		msize_t msize2 = small_mag_ptr->mag_last_free_msize;
 		region_t rgn2 = small_mag_ptr->mag_last_free_rgn;
 
 		/* check that we don't already have this pointer in the cache */
-		if (ptr == (void *)((uintptr_t)ptr2 & ~(SMALL_QUANTUM - 1))) {
-			free_small_botch(szone, ptr);
+		if (ptr == ptr2) {
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
+			free_small_botch(rack, ptr);
 			return;
 		}
 
-		if ((szone->debug_flags & MALLOC_DO_SCRIBBLE) && msize) {
+		if ((rack->debug_flags & MALLOC_DO_SCRIBBLE) && msize) {
 			memset(ptr, SCRABBLE_BYTE, SMALL_BYTES_FOR_MSIZE(msize));
 		}
 
-		small_mag_ptr->mag_last_free = (void *)(((uintptr_t)ptr) | msize);
+		small_mag_ptr->mag_last_free = ptr;
+		small_mag_ptr->mag_last_free_msize = msize;
 		small_mag_ptr->mag_last_free_rgn = small_region;
 
 		if (!ptr2) {
-			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 			CHECK(szone, __PRETTY_FUNCTION__);
 			return;
 		}
 
-		msize = (uintptr_t)ptr2 & (SMALL_QUANTUM - 1);
-		ptr = (void *)(((uintptr_t)ptr2) & ~(SMALL_QUANTUM - 1));
+		msize = msize2;
+		ptr = ptr2;
 		small_region = rgn2;
 	}
 #endif /* CONFIG_SMALL_CACHE */
@@ -1955,65 +2292,99 @@
 
 	while (mag_index != (refreshed_index = trailer->mag_index)) { // Note assignment
 
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 
 		mag_index = refreshed_index;
-		small_mag_ptr = &(szone->small_magazines[mag_index]);
-		SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
-	}
-
-	if (small_free_no_lock(szone, small_mag_ptr, mag_index, small_region, ptr, msize)) {
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+		small_mag_ptr = &(rack->magazines[mag_index]);
+		SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
+	}
+
+	if (small_free_no_lock(rack, small_mag_ptr, mag_index, small_region, ptr, msize)) {
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 	}
 
 	CHECK(szone, __PRETTY_FUNCTION__);
 }
 
 void
-print_small_free_list(szone_t *szone)
+print_small_free_list(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, rack_t *rack)
 {
 	free_list_t ptr;
 	_SIMPLE_STRING b = _simple_salloc();
 	mag_index_t mag_index;
 
 	if (b) {
-		_simple_sappend(b, "small free sizes:\n");
-		for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
+		rack_t *mapped_rack;
+		magazine_t *mapped_magazines;
+		if (reader(task, (vm_address_t)rack, sizeof(struct rack_s),
+				(void **)&mapped_rack)) {
+			printer("Failed to map small rack\n");
+			return;
+		}
+		if (reader(task, (vm_address_t)mapped_rack->magazines,
+				mapped_rack->num_magazines * sizeof(magazine_t),
+				(void **)&mapped_magazines)) {
+			printer("Failed to map small rack magazines\n");
+			return;
+		}
+
+        _simple_sappend(b, "small free sizes:\n");
+		grain_t free_slots = SMALL_FREE_SLOT_COUNT(mapped_rack);
+		for (mag_index = -1; mag_index < mapped_rack->num_magazines;
+				mag_index++) {
 			grain_t slot = 0;
-			_simple_sprintf(b, "\tMagazine %d: ", mag_index);
-			while (slot < szone->num_small_slots) {
-				ptr = szone->small_magazines[mag_index].mag_free_list[slot];
-				if (small_free_list_get_ptr(szone, ptr)) {
-					_simple_sprintf(b, "%s%y[%d]; ", (slot == szone->num_small_slots - 1) ? ">=" : "", (slot + 1) * SMALL_QUANTUM,
-									small_free_list_count(szone, ptr));
+			if (mag_index == -1) {
+				_simple_sprintf(b, "\tRecirc depot: ");
+			} else {
+				_simple_sprintf(b, "\tMagazine %d: ", mag_index);
+			}
+			while (slot < free_slots) {
+				ptr = mapped_magazines[mag_index].mag_free_list[slot];
+				if (small_free_list_get_ptr_task(task, reader, printer, ptr)) {
+					_simple_sprintf(b, "%s%y[%d]; ", (slot == free_slots - 1) ?
+							">=" : "", (slot + 1) * SMALL_QUANTUM,
+							small_free_list_count(task, reader, printer,
+									rack, ptr));
 				}
 				slot++;
 			}
 			_simple_sappend(b, "\n");
 		}
-		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
+		printer("%s\n", _simple_string(b));
 		_simple_sfree(b);
 	}
 }
 
 void
-print_small_region(szone_t *szone, boolean_t verbose, region_t region, size_t bytes_at_start, size_t bytes_at_end)
+print_small_region(task_t task, memory_reader_t reader,
+		print_task_printer_t printer, szone_t *szone, int level,
+		region_t region, size_t bytes_at_start, size_t bytes_at_end)
 {
 	unsigned counts[1024];
 	unsigned in_use = 0;
-	uintptr_t start = (uintptr_t)SMALL_REGION_ADDRESS(region);
+	uintptr_t start = (uintptr_t)SMALL_REGION_HEAP_BASE(region);
 	uintptr_t current = start + bytes_at_start;
-	uintptr_t limit = (uintptr_t)SMALL_REGION_END(region) - bytes_at_end;
+	uintptr_t limit = (uintptr_t)SMALL_REGION_HEAP_END(region) - bytes_at_end;
+	uintptr_t mapped_start;
 	msize_t msize_and_free;
 	msize_t msize;
 	unsigned ci;
 	_SIMPLE_STRING b;
 	uintptr_t pgTot = 0;
 
+	if (reader(task, (vm_address_t)start, SMALL_REGION_SIZE,
+			(void **)&mapped_start)) {
+		printer("Failed to map small region at %p\n", start);
+		return;
+	}
+	off_t start_offset = mapped_start - start;
+	region_t mapped_region = (region_t)mapped_start;
+
 	if (region == HASHRING_REGION_DEALLOCATED) {
 		if ((b = _simple_salloc()) != NULL) {
 			_simple_sprintf(b, "Small region [unknown address] was returned to the OS\n");
-			_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
+			printer("%s\n", _simple_string(b));
 			_simple_sfree(b);
 		}
 		return;
@@ -2021,10 +2392,11 @@
 
 	memset(counts, 0, sizeof(counts));
 	while (current < limit) {
-		msize_and_free = *SMALL_METADATA_FOR_PTR(current);
+		msize_and_free = *(uintptr_t *)((char *)SMALL_METADATA_FOR_PTR(current) + start_offset);
 		msize = msize_and_free & ~SMALL_IS_FREE;
 		if (!msize) {
-			malloc_printf("*** error with %p: msize=%d\n", (void *)current, (unsigned)msize);
+			printer("*** error with %p: msize=%d, free: %x\n", (void *)current,
+					(unsigned)msize, msize_and_free & SMALL_IS_FREE);
 			break;
 		}
 		if (!(msize_and_free & SMALL_IS_FREE)) {
@@ -2034,8 +2406,10 @@
 			}
 			in_use++;
 		} else {
-			uintptr_t pgLo = round_page_quanta(current + sizeof(free_list_t) + sizeof(msize_t));
-			uintptr_t pgHi = trunc_page_quanta(current + SMALL_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));
+			uintptr_t pgLo = round_page_quanta(current +
+					sizeof(free_list_t) + sizeof(msize_t));
+			uintptr_t pgHi = trunc_page_quanta(current +
+					SMALL_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));
 
 			if (pgLo < pgHi) {
 				pgTot += (pgHi - pgLo);
@@ -2043,74 +2417,95 @@
 		}
 		current += SMALL_BYTES_FOR_MSIZE(msize);
 	}
+
 	if ((b = _simple_salloc()) != NULL) {
-		_simple_sprintf(b, "Small region [%p-%p, %y] \t", (void *)start, SMALL_REGION_END(region), (int)SMALL_REGION_SIZE);
-		_simple_sprintf(b, "Magazine=%d \t", MAGAZINE_INDEX_FOR_SMALL_REGION(region));
-		_simple_sprintf(b, "Allocations in use=%d \t Bytes in use=%ly \t", in_use, BYTES_USED_FOR_SMALL_REGION(region));
+		mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(mapped_region);
+		_simple_sprintf(b, "Small region %p [%p-%p, %y] \t", region, (void *)start,
+				SMALL_REGION_HEAP_END(region), (int)SMALL_REGION_SIZE);
+		if (mag_index == DEPOT_MAGAZINE_INDEX) {
+			_simple_sprintf(b, "Recirc depot \t");
+		} else {
+		    _simple_sprintf(b, "Magazine=%d \t", mag_index);
+		}
+		_simple_sprintf(b, "Allocations in use=%d \t Bytes in use=%ly (%d%%) \t",
+				in_use, BYTES_USED_FOR_SMALL_REGION(mapped_region),
+				(int)(100.0F * BYTES_USED_FOR_SMALL_REGION(mapped_region))/SMALL_REGION_SIZE);
 		if (bytes_at_end || bytes_at_start) {
 			_simple_sprintf(b, "Untouched=%ly ", bytes_at_end + bytes_at_start);
 		}
-		if (DEPOT_MAGAZINE_INDEX == MAGAZINE_INDEX_FOR_SMALL_REGION(region)) {
+		if (mag_index == DEPOT_MAGAZINE_INDEX) {
 			_simple_sprintf(b, "Advised MADV_FREE=%ly", pgTot);
 		} else {
 			_simple_sprintf(b, "Fragments subject to reclamation=%ly", pgTot);
-		}
-		if (verbose && in_use) {
+#if CONFIG_RECIRC_DEPOT
+			_simple_sprintf(b, small_region_below_recirc_threshold(mapped_region) ?
+					"\tEmpty enough to be moved to recirc depot" :
+					"\tNot empty enough to be moved to recirc depot");
+#endif // CONFIG_RECIRC_DEPOT
+		}
+		if (level >= MALLOC_VERBOSE_PRINT_LEVEL && in_use) {
 			_simple_sappend(b, "\n\tSizes in use: ");
 			for (ci = 0; ci < 1024; ci++) {
 				if (counts[ci]) {
-					_simple_sprintf(b, "%d[%d] ", SMALL_BYTES_FOR_MSIZE(ci), counts[ci]);
+					_simple_sprintf(b, "%y[%d] ", SMALL_BYTES_FOR_MSIZE(ci),
+							counts[ci]);
 				}
 			}
 		}
-		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
+		printer("%s\n", _simple_string(b));
 		_simple_sfree(b);
 	}
 }
 
+static char *small_freelist_fail_msg = "check: small free list incorrect";
+
+#define SMALL_FREELIST_FAIL(fmt, ...) \
+	malloc_zone_check_fail(small_freelist_fail_msg, \
+			" (slot=%u), counter=%d\n" fmt,  slot, counter, __VA_ARGS__);
+
 boolean_t
-small_free_list_check(szone_t *szone, grain_t slot)
+small_free_list_check(rack_t *rack, grain_t slot, unsigned counter)
 {
 	mag_index_t mag_index;
 
-	for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
-		magazine_t *small_mag_ptr = &(szone->small_magazines[mag_index]);
-		SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
+	for (mag_index = -1; mag_index < rack->num_magazines; mag_index++) {
+		magazine_t *small_mag_ptr = &(rack->magazines[mag_index]);
+		SZONE_MAGAZINE_PTR_LOCK(small_mag_ptr);
 
 		unsigned count = 0;
-		free_list_t current = szone->small_magazines[mag_index].mag_free_list[slot];
+		free_list_t current = rack->magazines[mag_index].mag_free_list[slot];
 		free_list_t previous = (free_list_t){ .p = NULL };
 		msize_t msize_and_free;
 		void *ptr = NULL;
 
-		while ((ptr = small_free_list_get_ptr(szone, current))) {
+		while ((ptr = small_free_list_get_ptr(current))) {
 			msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
 			if (!(msize_and_free & SMALL_IS_FREE)) {
-				malloc_printf("*** in-use ptr in free list slot=%d count=%d ptr=%p\n", slot, count, ptr);
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+				SMALL_FREELIST_FAIL("*** in-use ptr in free list slot=%u count=%d ptr=%p\n", slot, count, ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				return 0;
 			}
 			if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
-				malloc_printf("*** unaligned ptr in free list slot=%d  count=%d ptr=%p\n", slot, count, ptr);
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+				SMALL_FREELIST_FAIL("*** unaligned ptr in free list slot=%u count=%d ptr=%p\n", slot, count, ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				return 0;
 			}
-			if (!small_region_for_ptr_no_lock(szone, ptr)) {
-				malloc_printf("*** ptr not in szone slot=%d  count=%d ptr=%p\n", slot, count, ptr);
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			if (!small_region_for_ptr_no_lock(rack, ptr)) {
+				SMALL_FREELIST_FAIL("*** ptr not in szone slot=%d count=%d ptr=%p\n", slot, count, ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				return 0;
 			}
-			if (small_free_list_get_previous(szone, current).p != previous.p) {
-				malloc_printf("*** previous incorrectly set slot=%d  count=%d ptr=%p\n", slot, count, ptr);
-				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+			if (small_free_list_get_previous(rack, current).p != previous.p) {
+				SMALL_FREELIST_FAIL("*** previous incorrectly set slot=%u count=%d ptr=%p\n", slot, count, ptr);
+				SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 				return 0;
 			}
 			previous = current;
-			current = small_free_list_get_next(szone, current);
+			current = small_free_list_get_next(rack, current);
 			count++;
 		}
-		
-		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
+
+		SZONE_MAGAZINE_PTR_UNLOCK(small_mag_ptr);
 	}
 	return 1;
 }