On Wed, Jun 24, 2009 at 12:30 PM, Eric Sandeen<sandeen@xxxxxxxxxx> 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:
>
> 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@xxxxxxxxxx>
> ---
>
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index cc7d5ed..9a438cf 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. target (a hint) */
> + ext4_fsblk_t goal;
> + /* phys. block for ^^^ */
> + ext4_fsblk_t pleft;
> /* phys. block for ^^^ */
> ext4_fsblk_t pright;
Hey Eric,
Looks like the comments for pleft and pright should be updated to
reference lleft and lright respectively (rather than ^^^).
Mike
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