btrfs: reduce compressed_bio members' types

Several members of compressed_bio are of type that's unnecessarily big
for the values that they'd hold:

- the size of the uncompressed and compressed data is 128K now, we can
  keep is as int
- same for number of pages
- the compress type fits to a byte
- the errors is 0/1

The size of the unpatched structure is 80 bytes with several holes.
Reordering nr_pages next to the pages the hole after pending_bios is
filled and the resulting size is 56 bytes. This keeps the csums array
aligned to 8 bytes, which is nice. Further size optimizations may be
possible but right now it looks good to me:

struct compressed_bio {
        refcount_t                 pending_bios;         /*     0     4 */
        unsigned int               nr_pages;             /*     4     4 */
        struct page * *            compressed_pages;     /*     8     8 */
        struct inode *             inode;                /*    16     8 */
        u64                        start;                /*    24     8 */
        unsigned int               len;                  /*    32     4 */
        unsigned int               compressed_len;       /*    36     4 */
        u8                         compress_type;        /*    40     1 */
        u8                         errors;               /*    41     1 */

        /* XXX 2 bytes hole, try to pack */

        int                        mirror_num;           /*    44     4 */
        struct bio *               orig_bio;             /*    48     8 */
        u8                         sums[];               /*    56     0 */

        /* size: 56, cachelines: 1, members: 12 */
        /* sum members: 54, holes: 1, sum holes: 2 */
        /* last cacheline: 56 bytes */
};

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 9a0c26e4e389..c006f5d81c2a 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -507,7 +507,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 		}
 		if (bytes_left < PAGE_SIZE) {
 			btrfs_info(fs_info,
-					"bytes left %lu compress len %lu nr %lu",
+					"bytes left %lu compress len %u nr %u",
 			       bytes_left, cb->compressed_len, cb->nr_pages);
 		}
 		bytes_left -= PAGE_SIZE;