Add a min size parameter to btrfs_alloc_extent

On huge machines, delayed allocation may try to allocate massive extents.
This change allows btrfs_alloc_extent to return something smaller than
the caller asked for, and the data allocation routines will loop over
the allocations until it fills the whole delayed alloc.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.h

@@ -1286,7 +1286,8 @@ int btrfs_insert_extent_backref(struct btrfs_trans_handle *trans,
 				 u64 owner, u64 owner_offset);
 int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *root,
-		       u64 num_bytes, u64 root_objectid, u64 ref_generation,
+		       u64 num_bytes, u64 min_bytes,
+		       u64 root_objectid, u64 ref_generation,
 		       u64 owner, u64 owner_offset,
 		       u64 empty_size, u64 hint_byte,
 		       u64 search_end, struct btrfs_key *ins, int data);

fs/btrfs/extent-tree.c

@@ -1694,7 +1694,8 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
  */
 int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *root,
-		       u64 num_bytes, u64 root_objectid, u64 ref_generation,
+		       u64 num_bytes, u64 min_alloc_size,
+		       u64 root_objectid, u64 ref_generation,
 		       u64 owner, u64 owner_offset,
 		       u64 empty_size, u64 hint_byte,
 		       u64 search_end, struct btrfs_key *ins, int data)
@@ -1727,7 +1728,7 @@ int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 			        info->metadata_alloc_profile;
 		data = BTRFS_BLOCK_GROUP_METADATA | alloc_profile;
 	}
-
+again:
 	if (root->ref_cows) {
 		if (!(data & BTRFS_BLOCK_GROUP_METADATA)) {
 			ret = do_chunk_alloc(trans, root->fs_info->extent_root,
@@ -1751,6 +1752,11 @@ int btrfs_alloc_extent(struct btrfs_trans_handle *trans,
 			       search_start, search_end, hint_byte, ins,
 			       trans->alloc_exclude_start,
 			       trans->alloc_exclude_nr, data);
+	if (ret == -ENOSPC && num_bytes > min_alloc_size) {
+		num_bytes = num_bytes >> 1;
+		num_bytes = max(num_bytes, min_alloc_size);
+		goto again;
+	}
 	BUG_ON(ret);
 	if (ret)
 		return ret;
@@ -1869,7 +1875,7 @@ struct extent_buffer *__btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
 	int ret;
 	struct extent_buffer *buf;
 
-	ret = btrfs_alloc_extent(trans, root, blocksize,
+	ret = btrfs_alloc_extent(trans, root, blocksize, blocksize,
 				 root_objectid, ref_generation,
 				 level, first_objectid, empty_size, hint,
 				 (u64)-1, &ins, 0);

fs/btrfs/inode.c

@@ -125,6 +125,7 @@ static int cow_file_range(struct inode *inode, u64 start, u64 end)
 	while(num_bytes > 0) {
 		cur_alloc_size = min(num_bytes, root->fs_info->max_extent);
 		ret = btrfs_alloc_extent(trans, root, cur_alloc_size,
+					 root->sectorsize,
 					 root->root_key.objectid,
 					 trans->transid,
 					 inode->i_ino, start, 0,
@@ -133,6 +134,7 @@ static int cow_file_range(struct inode *inode, u64 start, u64 end)
 			WARN_ON(1);
 			goto out;
 		}
+		cur_alloc_size = ins.offset;
 		ret = btrfs_insert_file_extent(trans, root, inode->i_ino,
 					       start, ins.objectid, ins.offset,
 					       ins.offset);