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
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -93,20 +93,20 @@
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;
};