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SubjectRe: [PATCH v2 2/5] mm: Extends local cpu counter vm_diff_nodestat from s8 to s16
On Tue 19-12-17 14:39:23, Kemi Wang wrote:
> The type s8 used for vm_diff_nodestat[] as local cpu counters has the
> limitation of global counters update frequency, especially for those
> monotone increasing type of counters like NUMA counters with more and more
> cpus/nodes. This patch extends the type of vm_diff_nodestat from s8 to s16
> without any functionality change.
>
> before after
> sizeof(struct per_cpu_nodestat) 28 68

So it is 40B * num_cpus * num_nodes. Nothing really catastrophic IMHO
but the changelog is a bit silent about any numbers. This is a
performance optimization so it should better give us some.

> Signed-off-by: Kemi Wang <kemi.wang@intel.com>
> ---
> include/linux/mmzone.h | 4 ++--
> mm/vmstat.c | 16 ++++++++--------
> 2 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index c06d880..2da6b6f 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -289,8 +289,8 @@ struct per_cpu_pageset {
> };
>
> struct per_cpu_nodestat {
> - s8 stat_threshold;
> - s8 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
> + s16 stat_threshold;
> + s16 vm_node_stat_diff[NR_VM_NODE_STAT_ITEMS];
> };
>
> #endif /* !__GENERATING_BOUNDS.H */
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 1dd12ae..9c681cc 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -332,7 +332,7 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
> long delta)
> {
> struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
> - s8 __percpu *p = pcp->vm_node_stat_diff + item;
> + s16 __percpu *p = pcp->vm_node_stat_diff + item;
> long x;
> long t;
>
> @@ -390,13 +390,13 @@ void __inc_zone_state(struct zone *zone, enum zone_stat_item item)
> void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
> {
> struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
> - s8 __percpu *p = pcp->vm_node_stat_diff + item;
> - s8 v, t;
> + s16 __percpu *p = pcp->vm_node_stat_diff + item;
> + s16 v, t;
>
> v = __this_cpu_inc_return(*p);
> t = __this_cpu_read(pcp->stat_threshold);
> if (unlikely(v > t)) {
> - s8 overstep = t >> 1;
> + s16 overstep = t >> 1;
>
> node_page_state_add(v + overstep, pgdat, item);
> __this_cpu_write(*p, -overstep);
> @@ -434,13 +434,13 @@ void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
> void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
> {
> struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
> - s8 __percpu *p = pcp->vm_node_stat_diff + item;
> - s8 v, t;
> + s16 __percpu *p = pcp->vm_node_stat_diff + item;
> + s16 v, t;
>
> v = __this_cpu_dec_return(*p);
> t = __this_cpu_read(pcp->stat_threshold);
> if (unlikely(v < - t)) {
> - s8 overstep = t >> 1;
> + s16 overstep = t >> 1;
>
> node_page_state_add(v - overstep, pgdat, item);
> __this_cpu_write(*p, overstep);
> @@ -533,7 +533,7 @@ static inline void mod_node_state(struct pglist_data *pgdat,
> enum node_stat_item item, int delta, int overstep_mode)
> {
> struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats;
> - s8 __percpu *p = pcp->vm_node_stat_diff + item;
> + s16 __percpu *p = pcp->vm_node_stat_diff + item;
> long o, n, t, z;
>
> do {
> --
> 2.7.4
>

--
Michal Hocko
SUSE Labs

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