[PATCH v2 3/3] btrfs: separate BLOCK_GROUP_TREE compat RO flag from EXTENT_TREE_V2

[Qu Wenruo <wqu@suse.com>]

The problem of long mount time caused by block group item search is
already known for over 7 years, and the solution of block group tree is
proposed at least for 5 years.

There is really no need to bound this feature into extent tree v2, just
introduce compat RO flag, BLOCK_GROUP_TREE, to correctly solve the
problem.

All the code handling block group root is already in the upstream
kernel, thus this patch really only needs to introduce the new compat RO
flag.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ctree.h           |  3 ++-
 fs/btrfs/disk-io.c         | 14 ++------------
 fs/btrfs/disk-io.h         |  2 +-
 fs/btrfs/sysfs.c           |  2 ++
 include/uapi/linux/btrfs.h |  6 ++++++
 5 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 7a1ff777f61b..94268c07dbfe 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -302,7 +302,8 @@ static_assert(sizeof(struct btrfs_super_block) == BTRFS_SUPER_INFO_SIZE);
 #define BTRFS_FEATURE_COMPAT_RO_SUPP			\
 	(BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE |	\
 	 BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID | \
-	 BTRFS_FEATURE_COMPAT_RO_VERITY)
+	 BTRFS_FEATURE_COMPAT_RO_VERITY |		\
+	 BTRFS_FEATURE_COMPAT_RO_BLOCK_GROUP_TREE)
 
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_SET	0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SAFE_CLEAR	0ULL
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 91d443755174..b925bb443e0d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2067,7 +2067,7 @@ static void backup_super_roots(struct btrfs_fs_info *info)
 	btrfs_set_backup_chunk_root_level(root_backup,
 			       btrfs_header_level(info->chunk_root->node));
 
-	if (!btrfs_fs_incompat(info, EXTENT_TREE_V2)) {
+	if (!btrfs_fs_compat_ro(info, BLOCK_GROUP_TREE)) {
 		struct btrfs_root *extent_root = btrfs_extent_root(info, 0);
 		struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
 
@@ -2612,7 +2612,7 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
 	location.type = BTRFS_ROOT_ITEM_KEY;
 	location.offset = 0;
 
-	if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
+	if (btrfs_fs_compat_ro(fs_info, BLOCK_GROUP_TREE)) {
 		location.objectid = BTRFS_BLOCK_GROUP_TREE_OBJECTID;
 		root = btrfs_read_tree_root(tree_root, &location);
 		if (IS_ERR(root)) {
@@ -2966,16 +2966,6 @@ static int __cold init_tree_roots(struct btrfs_fs_info *fs_info)
 	int ret = 0;
 	int i;
 
-	if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
-		struct btrfs_root *root;
-
-		root = btrfs_alloc_root(fs_info, BTRFS_BLOCK_GROUP_TREE_OBJECTID,
-					GFP_KERNEL);
-		if (!root)
-			return -ENOMEM;
-		fs_info->block_group_root = root;
-	}
-
 	for (i = 0; i < BTRFS_NUM_BACKUP_ROOTS; i++) {
 		if (handle_error) {
 			if (!IS_ERR(tree_root->node))
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 8993b428e09c..e7d289b0ed14 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -103,7 +103,7 @@ static inline struct btrfs_root *btrfs_grab_root(struct btrfs_root *root)
 
 static inline struct btrfs_root *btrfs_block_group_root(struct btrfs_fs_info *fs_info)
 {
-	if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2))
+	if (btrfs_fs_compat_ro(fs_info, BLOCK_GROUP_TREE))
 		return fs_info->block_group_root;
 	return btrfs_extent_root(fs_info, 0);
 }
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index d5d0717fd09a..b2eb6d40b21d 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -286,6 +286,7 @@ BTRFS_FEAT_ATTR_INCOMPAT(skinny_metadata, SKINNY_METADATA);
 BTRFS_FEAT_ATTR_INCOMPAT(no_holes, NO_HOLES);
 BTRFS_FEAT_ATTR_INCOMPAT(metadata_uuid, METADATA_UUID);
 BTRFS_FEAT_ATTR_COMPAT_RO(free_space_tree, FREE_SPACE_TREE);
+BTRFS_FEAT_ATTR_COMPAT_RO(block_group_tree, BLOCK_GROUP_TREE);
 BTRFS_FEAT_ATTR_INCOMPAT(raid1c34, RAID1C34);
 #ifdef CONFIG_BLK_DEV_ZONED
 BTRFS_FEAT_ATTR_INCOMPAT(zoned, ZONED);
@@ -316,6 +317,7 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
 	BTRFS_FEAT_ATTR_PTR(no_holes),
 	BTRFS_FEAT_ATTR_PTR(metadata_uuid),
 	BTRFS_FEAT_ATTR_PTR(free_space_tree),
+	BTRFS_FEAT_ATTR_PTR(block_group_tree),
 	BTRFS_FEAT_ATTR_PTR(raid1c34),
 #ifdef CONFIG_BLK_DEV_ZONED
 	BTRFS_FEAT_ATTR_PTR(zoned),
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index f54dc91e4025..5f79610e1c72 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -290,6 +290,12 @@ struct btrfs_ioctl_fs_info_args {
 #define BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE_VALID	(1ULL << 1)
 #define BTRFS_FEATURE_COMPAT_RO_VERITY			(1ULL << 2)
 
+/*
+ * Put all block group items into a dedicate block group tree, greatly
+ * reduce mount time for large fs.
+ */
+#define BTRFS_FEATURE_COMPAT_RO_BLOCK_GROUP_TREE	(1ULL << 5)
+
 #define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF	(1ULL << 0)
 #define BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL	(1ULL << 1)
 #define BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS	(1ULL << 2)
-- 
2.37.0