btrfs: rename btrfs_space_info_add_old_bytes

This name doesn't really fit with how the space reservation stuff works
now, rename it to btrfs_space_info_free_bytes_may_use so it's clear what
the function is doing.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-rsv.c

@@ -54,8 +54,9 @@ static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
 			spin_unlock(&dest->lock);
 		}
 		if (num_bytes)
-			btrfs_space_info_add_old_bytes(fs_info, space_info,
-						       num_bytes);
+			btrfs_space_info_free_bytes_may_use(fs_info,
+							    space_info,
+							    num_bytes);
 	}
 	if (qgroup_to_release_ret)
 		*qgroup_to_release_ret = qgroup_to_release;

fs/btrfs/delayed-ref.c

@@ -158,7 +158,7 @@ void btrfs_migrate_to_delayed_refs_rsv(struct btrfs_fs_info *fs_info,
 		trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",
 					      0, num_bytes, 1);
 	if (to_free)
-		btrfs_space_info_add_old_bytes(fs_info,
+		btrfs_space_info_free_bytes_may_use(fs_info,
 				delayed_refs_rsv->space_info, to_free);
 }
 

fs/btrfs/space-info.h

@@ -129,7 +129,7 @@ int btrfs_reserve_metadata_bytes(struct btrfs_root *root,
 void btrfs_try_granting_tickets(struct btrfs_fs_info *fs_info,
 				struct btrfs_space_info *space_info);
 
-static inline void btrfs_space_info_add_old_bytes(
+static inline void btrfs_space_info_free_bytes_may_use(
 				struct btrfs_fs_info *fs_info,
 				struct btrfs_space_info *space_info,
 				u64 num_bytes)