Btrfs: compression must free at least one sector size

We already skip storing data where compression does not make the result
at least one byte less.  Let's make the logic better and check
that compression frees at least one sector size of bytes, otherwise it's
not that useful.

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ changelog updated ]
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b74a6d23a0fe629818e5e5bf0af8c7c11280389a..a21a984d84d999b6ffd4745d249455b0237d6cb9 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -607,12 +607,11 @@ cont:
 
                /*
                 * one last check to make sure the compression is really a
-                * win, compare the page count read with the blocks on disk
+                * win, compare the page count read with the blocks on disk,
+                * compression must free at least one sector size
                 */
                total_in = ALIGN(total_in, PAGE_SIZE);
-               if (total_compressed >= total_in) {
-                       will_compress = 0;
-               } else {
+               if (total_compressed + blocksize <= total_in) {
                        num_bytes = total_in;
                        *num_added += 1;