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 <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/ext4.h

···
 struct ext4_allocation_request {
 	/* target inode for block we're allocating */
 	struct inode *inode;
-	/* 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 ^^^ */
-	ext4_fsblk_t pright;
 	/* how many blocks we want to allocate */
 	unsigned int len;
+	/* logical block in target inode */
+	ext4_lblk_t logical;
+	/* the closest logical allocated block to the left */
+	ext4_lblk_t lleft;
+	/* the closest logical allocated block to the right */
+	ext4_lblk_t lright;
+	/* 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;
 	/* flags. see above EXT4_MB_HINT_* */
 	unsigned int flags;
 };