On Fri, 15 Apr 2011 15:08:08 +0900
Namhyung Kim <namhyung@xxxxxxxxx> wrote:
> Remove duplicated reference to the 'current' task using a local
> variable. Since refering the current can be a burden, it'd better
> cache the reference, IMHO. At least this saves some bytes on x86_64.
>
> $ size mempolicy-{old,new}.o
> text data bss dec hex filename
> 25203 2448 9176 36827 8fdb mempolicy-old.o
> 25136 2448 9184 36768 8fa0 mempolicy-new.o
>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxx>
> ---
> mm/mempolicy.c | 58 +++++++++++++++++++++++++++++--------------------------
> 1 files changed, 31 insertions(+), 27 deletions(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 959a8b8c7350..5a30065590aa 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -304,6 +304,7 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes,
> enum mpol_rebind_step step)
> {
> nodemask_t tmp;
> + struct task_struct *tsk = current;
>
> if (pol->flags & MPOL_F_STATIC_NODES)
> nodes_and(tmp, pol->w.user_nodemask, *nodes);
> @@ -335,12 +336,12 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes,
> else
> BUG();
>
> - if (!node_isset(current->il_next, tmp)) {
> - current->il_next = next_node(current->il_next, tmp);
> - if (current->il_next >= MAX_NUMNODES)
> - current->il_next = first_node(tmp);
> - if (current->il_next >= MAX_NUMNODES)
> - current->il_next = numa_node_id();
> + if (!node_isset(tsk->il_next, tmp)) {
> + tsk->il_next = next_node(tsk->il_next, tmp);
> + if (tsk->il_next >= MAX_NUMNODES)
> + tsk->il_next = first_node(tmp);
> + if (tsk->il_next >= MAX_NUMNODES)
> + tsk->il_next = numa_node_id();
> }
> }
Odd. The new(ish) percpu_read_stable() stuff produces very efficient
code for `current' and usually means that caching `current' in a local
is unneeded, often an overall loss.
So... what is going wrong in mempolicy.c?
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>