diff --git a/Documentation/mkfs.btrfs.asciidoc b/Documentation/mkfs.btrfs.asciidoc
index 630f575c..8f1e1429 100644
--- a/Documentation/mkfs.btrfs.asciidoc
+++ b/Documentation/mkfs.btrfs.asciidoc
@@ -257,6 +257,12 @@ permanent, this does not replace mount options.
 Enable quota support (qgroups). The qgroup accounting will be consistent,
 can be used together with '--rootdir'.  See also `btrfs-quota`(8).
 
+*free_space_tree*::
+(kernel support since 3.4)
++
+Enable the free space tree (mount option space_cache=v2) for persisting the
+free space cache.
+
 BLOCK GROUPS, CHUNKS, RAID
 --------------------------
 
diff --git a/common/fsfeatures.c b/common/fsfeatures.c
index 48ab37ca..6c391806 100644
--- a/common/fsfeatures.c
+++ b/common/fsfeatures.c
@@ -104,9 +104,15 @@ static const struct btrfs_feature mkfs_features[] = {
 };
 
 static const struct btrfs_feature runtime_features[] = {
-	{ "quota", BTRFS_RUNTIME_FEATURE_QUOTA, NULL,
-		VERSION_TO_STRING2(3, 4), NULL, 0, NULL, 0,
+	{ "quota", BTRFS_RUNTIME_FEATURE_QUOTA,
+		"free_space_tree",
+		VERSION_TO_STRING2(3, 4),
+		VERSION_TO_STRING2(4, 9),
+		NULL, 0,
 		"quota support (qgroups)" },
+	{ "free-space-tree", BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE, NULL,
+		VERSION_TO_STRING2(4, 5), NULL, 0, NULL, 0,
+		"free space tree (space_cache=v2)" },
 	/* Keep this one last */
 	{ "list-all", BTRFS_FEATURE_LIST_ALL, NULL }
 };
diff --git a/common/fsfeatures.h b/common/fsfeatures.h
index 13141254..f76fc099 100644
--- a/common/fsfeatures.h
+++ b/common/fsfeatures.h
@@ -39,7 +39,8 @@
 
 #define BTRFS_FEATURE_LIST_ALL		(1ULL << 63)
 
-#define BTRFS_RUNTIME_FEATURE_QUOTA	(1ULL << 0)
+#define BTRFS_RUNTIME_FEATURE_QUOTA		(1ULL << 0)
+#define BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE	(1ULL << 1)
 
 void btrfs_list_all_fs_features(u64 mask_disallowed);
 void btrfs_list_all_runtime_features(u64 mask_disallowed);
diff --git a/kernel-shared/disk-io.c b/kernel-shared/disk-io.c
index 42f733e3..6f584986 100644
--- a/kernel-shared/disk-io.c
+++ b/kernel-shared/disk-io.c
@@ -1003,10 +1003,15 @@ int btrfs_setup_all_roots(struct btrfs_fs_info *fs_info, u64 root_tree_bytenr,
 		ret = find_and_setup_root(root, fs_info, BTRFS_FREE_SPACE_TREE_OBJECTID,
 					  fs_info->free_space_root);
 		if (ret) {
+			free(fs_info->free_space_root);
+			fs_info->free_space_root = NULL;
 			printk("Couldn't read free space tree\n");
 			return -EIO;
 		}
 		fs_info->free_space_root->track_dirty = 1;
+	} else {
+		free(fs_info->free_space_root);
+		fs_info->free_space_root = NULL;
 	}
 
 	ret = find_and_setup_log_root(root, fs_info, sb);
diff --git a/kernel-shared/free-space-tree.c b/kernel-shared/free-space-tree.c
index 3570a9ac..2edc7fc7 100644
--- a/kernel-shared/free-space-tree.c
+++ b/kernel-shared/free-space-tree.c
@@ -1433,6 +1433,7 @@ int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
 		goto abort;
 	}
 	fs_info->free_space_root = free_space_root;
+	add_root_to_dirty_list(free_space_root);
 
 	do {
 		block_group = btrfs_lookup_first_block_group(fs_info, start);
diff --git a/mkfs/main.c b/mkfs/main.c
index 18dc6f8e..3eb74821 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -34,6 +34,7 @@
 #include <blkid/blkid.h>
 #include "kernel-shared/ctree.h"
 #include "kernel-shared/disk-io.h"
+#include "kernel-shared/free-space-tree.h"
 #include "kernel-shared/volumes.h"
 #include "kernel-shared/transaction.h"
 #include "common/utils.h"
@@ -1495,6 +1496,13 @@ raid_groups:
 			goto out;
 		}
 	}
+	if (runtime_features & BTRFS_RUNTIME_FEATURE_FREE_SPACE_TREE) {
+		ret = btrfs_create_free_space_tree(fs_info);
+		if (ret < 0) {
+			error("failed to create free space tree: %d (%m)", ret);
+			goto out;
+		}
+	}
 	if (verbose) {
 		char features_buf[64];
 
diff --git a/tests/mkfs-tests/023-free-space-tree/test.sh b/tests/mkfs-tests/023-free-space-tree/test.sh
new file mode 100755
index 00000000..1b40325a
--- /dev/null
+++ b/tests/mkfs-tests/023-free-space-tree/test.sh
@@ -0,0 +1,21 @@
+#!/bin/bash
+# Check if mkfs supports the runtime feature free_space_tree
+
+source "$TEST_TOP/common"
+
+check_prereq mkfs.btrfs
+check_prereq btrfs
+
+setup_root_helper
+
+setup_loopdevs 4
+prepare_loopdevs
+dev1=${loopdevs[1]}
+
+run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f -R free-space-tree "$dev1"
+run_check_stdout $SUDO_HELPER "$TOP/btrfs" inspect-internal dump-super "$dev1" | grep -q FREE_SPACE_TREE || _fail "free space tree not created"
+run_check_stdout $SUDO_HELPER "$TOP/btrfs" inspect-internal dump-super "$dev1" | grep -q FREE_SPACE_TREE_VALID || _fail "free space tree not valid"
+
+cleanup_loopdevs
+
+exit 0
