btrfs: reject single block sized compression early

Currently for an inode that needs compression, even if there is a delalloc
range that is single fs block sized and can not be inlined, we will
still go through the compression path.

Then inside compress_file_range(), we have one extra check to reject
single block sized range, and fall back to regular uncompressed write.

This rejection is in fact a little too late, we have already allocated
memory to async_chunk, delayed the submission, just to fallback to the
same uncompressed write.

Change the behavior to reject such cases earlier at
inode_need_compress(), so for such single block sized range we won't
even bother trying to go through compress path.

And since the inline small block check is inside inode_need_compress()
and compress_file_range() also calls that function, we no longer need a
dedicate check inside compress_file_range().

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 8 insertions, 12 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 247b373bf5cf..be47aa58e944 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -816,6 +816,13 @@ static inline int inode_need_compress(struct btrfs_inode *inode, u64 start,
 		return 0;
 	}
 
+	/*
+	 * If the delalloc range is only one fs block and can not be inlined,
+	 * do not even bother try compression, as there will be no space saving
+	 * and will always fallback to regular write later.
+	 */
+	if (start != 0 && end + 1 - start <= fs_info->sectorsize)
+		return 0;
 	/* Defrag ioctl takes precedence over mount options and properties. */
 	if (inode->defrag_compress == BTRFS_DEFRAG_DONT_COMPRESS)
 		return 0;
@@ -953,18 +960,7 @@ again:
 	if (actual_end <= start)
 		goto cleanup_and_bail_uncompressed;
 
-	total_compressed = actual_end - start;
-
-	/*
-	 * Skip compression for a small file range(<=blocksize) that
-	 * isn't an inline extent, since it doesn't save disk space at all.
-	 */
-	if (total_compressed <= blocksize &&
-	   (start > 0 || end + 1 < inode->disk_i_size))
-		goto cleanup_and_bail_uncompressed;
-
-	total_compressed = min_t(unsigned long, total_compressed,
-			BTRFS_MAX_UNCOMPRESSED);
+	total_compressed = min_t(unsigned long, actual_end - start, BTRFS_MAX_UNCOMPRESSED);
 	total_in = 0;
 	ret = 0;