btrfs: remove no longer used btrfs_migrate_to_delayed_refs_rsv()

The function btrfs_migrate_to_delayed_refs_rsv() is no longer used.
Its last use was removed in commit 2f6397e4 ("btrfs: don't refill
whole delayed refs block reserve when starting transaction").
So remove the function.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/delayed-ref.c

@@ -194,48 +194,6 @@ void btrfs_dec_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info)
 					      0, released, 0);
 }
 
-/*
- * Transfer bytes to our delayed refs rsv.
- *
- * @fs_info:   the filesystem
- * @num_bytes: number of bytes to transfer
- *
- * This transfers up to the num_bytes amount, previously reserved, to the
- * delayed_refs_rsv.  Any extra bytes are returned to the space info.
- */
-void btrfs_migrate_to_delayed_refs_rsv(struct btrfs_fs_info *fs_info,
-				       u64 num_bytes)
-{
-	struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
-	u64 to_free = 0;
-
-	spin_lock(&delayed_refs_rsv->lock);
-	if (delayed_refs_rsv->size > delayed_refs_rsv->reserved) {
-		u64 delta = delayed_refs_rsv->size -
-			delayed_refs_rsv->reserved;
-		if (num_bytes > delta) {
-			to_free = num_bytes - delta;
-			num_bytes = delta;
-		}
-	} else {
-		to_free = num_bytes;
-		num_bytes = 0;
-	}
-
-	if (num_bytes)
-		delayed_refs_rsv->reserved += num_bytes;
-	if (delayed_refs_rsv->reserved >= delayed_refs_rsv->size)
-		delayed_refs_rsv->full = true;
-	spin_unlock(&delayed_refs_rsv->lock);
-
-	if (num_bytes)
-		trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",
-					      0, num_bytes, 1);
-	if (to_free)
-		btrfs_space_info_free_bytes_may_use(fs_info,
-				delayed_refs_rsv->space_info, to_free);
-}
-
 /*
  * Refill based on our delayed refs usage.
  *

fs/btrfs/delayed-ref.h

@@ -386,8 +386,6 @@ void btrfs_inc_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info);
 void btrfs_dec_delayed_refs_rsv_bg_updates(struct btrfs_fs_info *fs_info);
 int btrfs_delayed_refs_rsv_refill(struct btrfs_fs_info *fs_info,
 				  enum btrfs_reserve_flush_enum flush);
-void btrfs_migrate_to_delayed_refs_rsv(struct btrfs_fs_info *fs_info,
-				       u64 num_bytes);
 bool btrfs_check_space_for_delayed_refs(struct btrfs_fs_info *fs_info);
 
 static inline u64 btrfs_delayed_ref_owner(struct btrfs_delayed_ref_node *node)