Hi Aaron, On Mon, Aug 08, 2022 at 08:48:19PM +0100, Aaron Tomlin wrote: > This patch incorporates an idea from Marcelo's patch [1] where a > CPU-specific variable namely vmstat_dirty is used to indicate if > a vmstat imbalance is present for a given CPU. Therefore, at the > appropriate time, we can fold all the remaining differentials. > > [1]: https://lore.kernel.org/lkml/20220204173554.763888172@fedora.localdomain/ > > Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx> > --- > mm/vmstat.c | 46 +++++++++++++++------------------------------- > 1 file changed, 15 insertions(+), 31 deletions(-) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 373d2730fcf2..51564b7c85fe 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -195,6 +195,12 @@ void fold_vm_numa_events(void) > #endif > > #ifdef CONFIG_SMP > +static DEFINE_PER_CPU_ALIGNED(bool, vmstat_dirty); > + > +static inline void mark_vmstat_dirty(void) > +{ > + this_cpu_write(vmstat_dirty, true); > +} > > int calculate_pressure_threshold(struct zone *zone) > { > @@ -367,6 +373,7 @@ void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item, > x = 0; > } > __this_cpu_write(*p, x); > + mark_vmstat_dirty(); > > if (IS_ENABLED(CONFIG_PREEMPT_RT)) > preempt_enable(); > @@ -405,6 +412,7 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, > x = 0; > } > __this_cpu_write(*p, x); > + mark_vmstat_dirty(); > > if (IS_ENABLED(CONFIG_PREEMPT_RT)) > preempt_enable(); > @@ -603,6 +611,7 @@ static inline void mod_zone_state(struct zone *zone, > > if (z) > zone_page_state_add(z, zone, item); > + mark_vmstat_dirty(); > } > > void mod_zone_page_state(struct zone *zone, enum zone_stat_item item, > @@ -671,6 +680,7 @@ static inline void mod_node_state(struct pglist_data *pgdat, > > if (z) > node_page_state_add(z, pgdat, item); > + mark_vmstat_dirty(); > } > > void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, > @@ -1873,6 +1883,7 @@ int sysctl_stat_interval __read_mostly = HZ; > static void refresh_vm_stats(struct work_struct *work) > { > refresh_cpu_vm_stats(true); Another task can be scheduled here, set data in zone->per_cpu_zonestats->vm_stat_diff (after refresh_cpu_vm_stats has cleared it to zero), and you'll end up marking per-CPU vmstat_dirty bool as false incorrectly. Guess it is necessary to disable preemption here. > + this_cpu_write(vmstat_dirty, false); > } > > int vmstat_refresh(struct ctl_table *table, int write, > @@ -1937,6 +1948,7 @@ int vmstat_refresh(struct ctl_table *table, int write, > static void vmstat_update(struct work_struct *w) > { > if (refresh_cpu_vm_stats(true)) { > + this_cpu_write(vmstat_dirty, false); Same problem. > /* > * Counters were updated so we expect more updates > * to occur in the future. Keep on running the > @@ -1948,35 +1960,6 @@ static void vmstat_update(struct work_struct *w) > } > } > > -/* > - * Check if the diffs for a certain cpu indicate that > - * an update is needed. > - */ > -static bool need_update(int cpu) > -{ > - pg_data_t *last_pgdat = NULL; > - struct zone *zone; > - > - for_each_populated_zone(zone) { > - struct per_cpu_zonestat *pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu); > - struct per_cpu_nodestat *n; > - > - /* > - * The fast way of checking if there are any vmstat diffs. > - */ > - if (memchr_inv(pzstats->vm_stat_diff, 0, sizeof(pzstats->vm_stat_diff))) > - return true; > - > - if (last_pgdat == zone->zone_pgdat) > - continue; > - last_pgdat = zone->zone_pgdat; > - n = per_cpu_ptr(zone->zone_pgdat->per_cpu_nodestats, cpu); > - if (memchr_inv(n->vm_node_stat_diff, 0, sizeof(n->vm_node_stat_diff))) > - return true; > - } > - return false; > -} > - > /* > * Switch off vmstat processing and then fold all the remaining differentials > * until the diffs stay at zero. The function is used by NOHZ and can only be > @@ -1990,7 +1973,7 @@ void quiet_vmstat(void) > if (!delayed_work_pending(this_cpu_ptr(&vmstat_work))) > return; > > - if (!need_update(smp_processor_id())) > + if (!__this_cpu_read(vmstat_dirty)) > return; > > /* > @@ -2000,6 +1983,7 @@ void quiet_vmstat(void) > * vmstat_shepherd will take care about that for us. > */ > refresh_cpu_vm_stats(false); > + __this_cpu_write(vmstat_dirty, false); > } >From this context, irqs should be disabled. > /* > @@ -2021,7 +2005,7 @@ static void vmstat_shepherd(struct work_struct *w) > for_each_online_cpu(cpu) { > struct delayed_work *dw = &per_cpu(vmstat_work, cpu); > > - if (!delayed_work_pending(dw) && need_update(cpu)) > + if (!delayed_work_pending(dw) && per_cpu(vmstat_dirty, cpu)) > queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0); > > cond_resched(); > -- > 2.37.1 > >
