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 <[email protected]> > --- > 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
