From: Aaron Tomlin <atomlin@xxxxxxxxxxx> This patch will now use the previously introduced CPU-specific variable namely vmstat_dirty to indicate if a vmstat differential/or imbalance is present for a given CPU. So, at the appropriate time, vmstat processing can be initiated. The hope is that this particular approach is "cheaper" when compared to need_update(). The idea is based on Marcelo's patch [1]. [1]: https://lore.kernel.org/lkml/20220204173554.763888172@fedora.localdomain/ Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxxx> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> --- mm/vmstat.c | 48 ++++++++++++++---------------------------------- 1 file changed, 14 insertions(+), 34 deletions(-) Index: linux-2.6/mm/vmstat.c =================================================================== --- linux-2.6.orig/mm/vmstat.c +++ linux-2.6/mm/vmstat.c @@ -381,6 +381,7 @@ void __mod_zone_page_state(struct zone * x = 0; } __this_cpu_write(*p, x); + vmstat_mark_dirty(); preempt_enable_nested(); } @@ -417,6 +418,7 @@ void __mod_node_page_state(struct pglist x = 0; } __this_cpu_write(*p, x); + vmstat_mark_dirty(); preempt_enable_nested(); } @@ -577,6 +579,9 @@ static inline void mod_zone_state(struct s8 __percpu *p = pcp->vm_stat_diff + item; long o, n, t, z; + /* cmpxchg and vmstat_mark_dirty should happen on the same CPU */ + preempt_disable(); + do { z = 0; /* overflow to zone counters */ @@ -606,6 +611,8 @@ static inline void mod_zone_state(struct if (z) zone_page_state_add(z, zone, item); + vmstat_mark_dirty(); + preempt_enable(); } void mod_zone_page_state(struct zone *zone, enum zone_stat_item item, @@ -645,6 +652,8 @@ static inline void mod_node_state(struct delta >>= PAGE_SHIFT; } + /* cmpxchg and vmstat_mark_dirty should happen on the same CPU */ + preempt_disable(); do { z = 0; /* overflow to node counters */ @@ -674,6 +683,8 @@ static inline void mod_node_state(struct if (z) node_page_state_add(z, pgdat, item); + vmstat_mark_dirty(); + preempt_enable(); } void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, @@ -828,6 +839,14 @@ static int refresh_cpu_vm_stats(bool do_ int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, }; int changes = 0; + /* + * Clear vmstat_dirty before clearing the percpu vmstats. + * If interrupts are enabled, it is possible that an interrupt + * or another task modifies a percpu vmstat, which will + * set vmstat_dirty to true. + */ + vmstat_clear_dirty(); + for_each_populated_zone(zone) { struct per_cpu_zonestat __percpu *pzstats = zone->per_cpu_zonestats; #ifdef CONFIG_NUMA @@ -1957,35 +1976,6 @@ static void vmstat_update(struct work_st } /* - * 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 * invoked when tick processing is not active. @@ -1995,10 +1985,7 @@ void quiet_vmstat(void) if (system_state != SYSTEM_RUNNING) return; - if (!delayed_work_pending(this_cpu_ptr(&vmstat_work))) - return; - - if (!need_update(smp_processor_id())) + if (!is_vmstat_dirty()) return; /* @@ -2029,7 +2016,7 @@ static void vmstat_shepherd(struct work_ 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();
