env: Add spdk_mem_reserve

The spdk_mem_reserve() function reserves a memory region in SPDK's
memory maps. This pre-allocates all of the required data structures
to hold memory address translations for that region without actually
populating the region.

After a region is reserved, calls to spdk_mem_register() for
addresses in that range will not require any internal memory
allocations. This is useful when overlaying a custom memory allocator
on top of SPDK's hugepage memory, such as tcmalloc.

Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Change-Id: Ia4e8a770e8b5c956814aa90e9119013356dfab46
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/2511
Community-CI: Mellanox Build Bot
Community-CI: Broadcom CI
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>

include/spdk/env.h

@@ -1248,6 +1248,20 @@ int spdk_mem_register(void *vaddr, size_t len);
  */
 int spdk_mem_unregister(void *vaddr, size_t len);
 
+/**
+ * Reserve the address space specified in all memory maps.
+ *
+ * This pre-allocates the necessary space in the memory maps such that
+ * future calls to spdk_mem_register() on that region require no
+ * internal memory allocations.
+ *
+ * \param vaddr Virtual address to reserve
+ * \param len Length in bytes of vaddr
+ *
+ * \return 0 on success, negated errno on failure.
+ */
+int spdk_mem_reserve(void *vaddr, size_t len);
+
 #ifdef __cplusplus
 }
 #endif

lib/env_dpdk/memory.c

@@ -509,6 +509,57 @@ spdk_mem_unregister(void *vaddr, size_t len)
 	return 0;
 }
 
+int
+spdk_mem_reserve(void *vaddr, size_t len)
+{
+	struct spdk_mem_map *map;
+	void *seg_vaddr;
+	size_t seg_len;
+	uint64_t reg;
+
+	if ((uintptr_t)vaddr & ~MASK_256TB) {
+		DEBUG_PRINT("invalid usermode virtual address %p\n", vaddr);
+		return -EINVAL;
+	}
+
+	if (((uintptr_t)vaddr & MASK_2MB) || (len & MASK_2MB)) {
+		DEBUG_PRINT("invalid %s parameters, vaddr=%p len=%ju\n",
+			    __func__, vaddr, len);
+		return -EINVAL;
+	}
+
+	if (len == 0) {
+		return 0;
+	}
+
+	pthread_mutex_lock(&g_spdk_mem_map_mutex);
+
+	/* Check if any part of this range is already registered */
+	seg_vaddr = vaddr;
+	seg_len = len;
+	while (seg_len > 0) {
+		reg = spdk_mem_map_translate(g_mem_reg_map, (uint64_t)seg_vaddr, NULL);
+		if (reg & REG_MAP_REGISTERED) {
+			pthread_mutex_unlock(&g_spdk_mem_map_mutex);
+			return -EBUSY;
+		}
+		seg_vaddr += VALUE_2MB;
+		seg_len -= VALUE_2MB;
+	}
+
+	/* Simply set the translation to the memory map's default. This allocates the space in the
+	 * map but does not provide a valid translation. */
+	spdk_mem_map_set_translation(g_mem_reg_map, (uint64_t)vaddr, len,
+				     g_mem_reg_map->default_translation);
+
+	TAILQ_FOREACH(map, &g_spdk_mem_maps, tailq) {
+		spdk_mem_map_set_translation(map, (uint64_t)vaddr, len, map->default_translation);
+	}
+
+	pthread_mutex_unlock(&g_spdk_mem_map_mutex);
+	return 0;
+}
+
 static struct map_1gb *
 spdk_mem_map_get_map_1gb(struct spdk_mem_map *map, uint64_t vfn_2mb)
 {