Btrfs: record first logical byte in memory

This'd save us a rbtree search which may become expensive in large filesystem.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

3 files changed, 20 insertions, 1 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 22f012d41fd0..9ee099f3f834 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1250,6 +1250,7 @@ struct btrfs_fs_info {
 
         /* block group cache stuff */
         spinlock_t block_group_cache_lock;
+        u64 first_logical_byte;
         struct rb_root block_group_cache_tree;
 
         /* keep track of unallocated space */
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1db8a9938829..04f98e3ffd90 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2130,6 +2130,7 @@ int open_ctree(struct super_block *sb,
 
         spin_lock_init(&fs_info->block_group_cache_lock);
         fs_info->block_group_cache_tree = RB_ROOT;
+        fs_info->first_logical_byte = (u64)-1;
 
         extent_io_tree_init(&fs_info->freed_extents[0],
                              fs_info->btree_inode->i_mapping);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 825f23b13b58..82400b2b2517 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -161,6 +161,10 @@ static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
         rb_link_node(&block_group->cache_node, parent, p);
         rb_insert_color(&block_group->cache_node,
                         &info->block_group_cache_tree);
+
+        if (info->first_logical_byte > block_group->key.objectid)
+                info->first_logical_byte = block_group->key.objectid;
+
         spin_unlock(&info->block_group_cache_lock);
 
         return 0;
@@ -202,8 +206,11 @@ block_group_cache_tree_search(struct btrfs_fs_info *info, u64 bytenr,
                         break;
                 }
         }
-        if (ret)
+        if (ret) {
                 btrfs_get_block_group(ret);
+                if (bytenr == 0 && info->first_logical_byte > ret->key.objectid)
+                        info->first_logical_byte = ret->key.objectid;
+        }
         spin_unlock(&info->block_group_cache_lock);
 
         return ret;
@@ -4848,6 +4855,13 @@ static u64 first_logical_byte(struct btrfs_root *root, u64 search_start)
         struct btrfs_block_group_cache *cache;
         u64 bytenr;
 
+        spin_lock(&root->fs_info->block_group_cache_lock);
+        bytenr = root->fs_info->first_logical_byte;
+        spin_unlock(&root->fs_info->block_group_cache_lock);
+
+        if (bytenr < (u64)-1)
+                return bytenr;
+
         cache = btrfs_lookup_first_block_group(root->fs_info, search_start);
         if (!cache)
                 return 0;
@@ -8059,6 +8073,9 @@ int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
         spin_lock(&root->fs_info->block_group_cache_lock);
         rb_erase(&block_group->cache_node,
                  &root->fs_info->block_group_cache_tree);
+
+        if (root->fs_info->first_logical_byte == block_group->key.objectid)
+                root->fs_info->first_logical_byte = (u64)-1;
         spin_unlock(&root->fs_info->block_group_cache_lock);
 
         down_write(&block_group->space_info->groups_sem);