[PATCH v2] btrfs: extent-tree: Remove dead alignment check

[PATCH v2] btrfs: extent-tree: Remove dead alignment check

[Qu Wenruo]

In find_free_extent() under checks: tag, we have the following code

------
		search_start = ALIGN(offset, fs_info->stripesize);
		/* move on to the next group */
		if (search_start + num_bytes >
		    block_group->key.objectid + block_group->key.offset) {
			btrfs_add_free_space(block_group, offset, num_bytes);
			goto loop;
		}
		if (offset < search_start)
			btrfs_add_free_space(block_group, offset,
					     search_start - offset);
		BUG_ON(offset > search_start);
------

However ALIGN() is rounding up, thus @search_start >= @offset and that
BUG_ON() will never be triggered.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
changelog:
v2:
  Fix my stupid error on judging whether ALIGN() is rounding up or down.
---
 fs/btrfs/extent-tree.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f18e86177067..de4a85dfb98e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7754,7 +7754,7 @@ static noinline int find_free_extent(struct btrfs_fs_info *fs_info,
 			goto loop;
 		}
 checks:
-		search_start = ALIGN(offset, fs_info->stripesize);
+		search_start = round_up(offset, fs_info->stripesize);
 
 		/* move on to the next group */
 		if (search_start + num_bytes >
@@ -7766,7 +7766,6 @@ static noinline int find_free_extent(struct btrfs_fs_info *fs_info,
 		if (offset < search_start)
 			btrfs_add_free_space(block_group, offset,
 					     search_start - offset);
-		BUG_ON(offset > search_start);
 
 		ret = btrfs_add_reserved_bytes(block_group, ram_bytes,
 				num_bytes, delalloc);
-- 
2.18.0

Re: [PATCH v2] btrfs: extent-tree: Remove dead alignment check

[David Sterba]

On Mon, Jul 23, 2018 at 02:47:29PM +0800, Qu Wenruo wrote:
> In find_free_extent() under checks: tag, we have the following code
> 
> ------
> 		search_start = ALIGN(offset, fs_info->stripesize);
> 		/* move on to the next group */
> 		if (search_start + num_bytes >
> 		    block_group->key.objectid + block_group->key.offset) {
> 			btrfs_add_free_space(block_group, offset, num_bytes);
> 			goto loop;
> 		}
> 		if (offset < search_start)
> 			btrfs_add_free_space(block_group, offset,
> 					     search_start - offset);
> 		BUG_ON(offset > search_start);
> ------
> 
> However ALIGN() is rounding up, thus @search_start >= @offset and that
> BUG_ON() will never be triggered.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: David Sterba <dsterba@suse.com>