diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b3ecca447ddf8..d2b3a5e9a6211 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6143,7 +6143,7 @@ int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
 	if (ret == -ENOSPC) {
 		if (!final_tried) {
 			num_bytes = num_bytes >> 1;
-			num_bytes = num_bytes & ~(root->sectorsize - 1);
+			num_bytes = round_down(num_bytes, root->sectorsize);
 			num_bytes = max(num_bytes, min_alloc_size);
 			if (num_bytes == min_alloc_size)
 				final_tried = true;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4e6a11c2cfdda..3bc62b181ef83 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7894,8 +7894,9 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
 			}
 		}
 
-		ret = btrfs_reserve_extent(trans, root, num_bytes, min_size,
-					   0, *alloc_hint, &ins, 1);
+		ret = btrfs_reserve_extent(trans, root,
+					   min(num_bytes, 256ULL * 1024 * 1024),
+					   min_size, 0, *alloc_hint, &ins, 1);
 		if (ret) {
 			if (own_trans)
 				btrfs_end_transaction(trans, root);