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| H A D | ext4.h | 726447d8 Mon Jul 13 09:24:17 CDT 2009 Eric Sandeen <sandeen@redhat.com> 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>
726447d8 Mon Jul 13 09:24:17 CDT 2009 Eric Sandeen <sandeen@redhat.com> 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>
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