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>

1 files changed, 7 insertions, 7 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0ddf7e55abe1..9714db393efe 100644
--- 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;
 };