On Fri, 10 Jul 2015 14:26:21 +0800 Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx> wrote:
> nr_node_ids records the highest possible node id, which is calculated by
> scanning the bitmap node_states[N_POSSIBLE]. Current implementation scan
> the bitmap from the beginning, which will scan the whole bitmap.
>
> This patch reverse the order by scanning from the end. By doing so, this
> will save some time whose worst case is the best case of current
> implementation.
It hardly matters - setup_nr_node_ids() is called a single time, at boot.
> --- a/include/linux/nodemask.h
> +++ b/include/linux/nodemask.h
> @@ -253,6 +253,12 @@ static inline int __first_node(const nodemask_t *srcp)
> return min_t(int, MAX_NUMNODES, find_first_bit(srcp->bits, MAX_NUMNODES));
> }
>
> +#define last_node(src) __last_node(&(src))
> +static inline int __last_node(const nodemask_t *srcp)
> +{
> + return min_t(int, MAX_NUMNODES, find_last_bit(srcp->bits, MAX_NUMNODES));
> +}
hm. Why isn't this just
return find_last_bit(srcp->bits, MAX_NUMNODES);
?
> @@ -360,10 +366,20 @@ static inline void __nodes_fold(nodemask_t *dstp, const nodemask_t *origp,
> for ((node) = first_node(mask); \
> (node) < MAX_NUMNODES; \
> (node) = next_node((node), (mask)))
> +
> +static inline int highest_node_id(const nodemask_t possible)
> +{
> + return last_node(possible);
> +}
`possible' isn't a good identifier. This function doesn't *know* that
its caller passed node_possible_map. Another caller could pass some
other nodemask.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5453,8 +5453,7 @@ void __init setup_nr_node_ids(void)
> unsigned int node;
> unsigned int highest = 0;
The "= 0" can now be removed.
> - for_each_node_mask(node, node_possible_map)
> - highest = node;
> + highest = highest_node_id(node_possible_map);
I suspect we can just open-code a find_last_bit() here and all the
infrastructure isn't needed.
> nr_node_ids = highest + 1;
> }
And I suspect the "#if MAX_NUMNODES > 1" around setup_nr_node_ids() can
be removed. Because if MAX_NUMNODES is ever <= 1 when
CONFIG_HAVE_MEMBLOCK_NODE_MAP=y, the kernel won't compile.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>