ext4: naturally align struct ext4_allocation_request

As Ted noted, the ext4_allocation_request isn't well aligned.  Looking
at it with pahole we're wasting space on 64-bit arches:

struct ext4_allocation_request {
        struct inode *             inode;              /*     0     8 */
        ext4_lblk_t                logical;            /*     8     4 */

        /* XXX 4 bytes hole, try to pack */

        ext4_fsblk_t               goal;               /*    16     8 */
        ext4_lblk_t                lleft;              /*    24     4 */

        /* XXX 4 bytes hole, try to pack */

        ext4_fsblk_t               pleft;              /*    32     8 */
        ext4_lblk_t                lright;             /*    40     4 */

        /* XXX 4 bytes hole, try to pack */

        ext4_fsblk_t               pright;             /*    48     8 */
        unsigned int               len;                /*    56     4 */
        unsigned int               flags;              /*    60     4 */
        /* --- cacheline 1 boundary (64 bytes) --- */

        /* size: 64, cachelines: 1, members: 9 */
        /* sum members: 52, holes: 3, sum holes: 12 */
};

Grouping 32-bit members together closes these holes and shrinks the
structure by 12 bytes. which is important since ext4 can get on the
hairy edge of stack overruns.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0ddf7e5..9714db3 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -93,20 +93,20 @@ typedef unsigned int ext4_group_t;
 struct ext4_allocation_request {
        /* target inode for block we're allocating */
        struct inode *inode;
+       /* how many blocks we want to allocate */
+       unsigned int len;
        /* logical block in target inode */
        ext4_lblk_t logical;
-       /* phys. target (a hint) */
-       ext4_fsblk_t goal;
        /* the closest logical allocated block to the left */
        ext4_lblk_t lleft;
-       /* phys. block for ^^^ */
-       ext4_fsblk_t pleft;
        /* the closest logical allocated block to the right */
        ext4_lblk_t lright;
-       /* phys. block for ^^^ */
+       /* phys. target (a hint) */
+       ext4_fsblk_t goal;
+       /* phys. block for the closest logical allocated block to the left */
+       ext4_fsblk_t pleft;
+       /* phys. block for the closest logical allocated block to the right */
        ext4_fsblk_t pright;
-       /* how many blocks we want to allocate */
-       unsigned int len;
        /* flags. see above EXT4_MB_HINT_* */
        unsigned int flags;
 };