diff mbox

[V2] naturally align struct ext4_allocation_request

Message ID 4A441FD4.9020403@redhat.com
State Accepted, archived
Headers show

Commit Message

Eric Sandeen June 26, 2009, 1:09 a.m. UTC 
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.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

V2: fix comments, thanks to Mike Snitzer


--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Comments

Theodore Ts'o July 6, 2009, 2:24 a.m. UTC | #1 
On Thu, Jun 25, 2009 at 08:09:40PM -0500, Eric Sandeen wrote:
> As Ted noted, the ext4_allocation_request isn't well aligned.
> 
> Looking at it with pahole we're wasting space on 64-bit
> arches...
> grouping 32-bit members together closes these holes and shrinks
> the structure by 12 bytes.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>


Thanks, added to the ext4 patch queue.

						- Ted

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
diff mbox

Patch

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cc7d5ed..cefd94a 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;
 };