linux-kernel - [PATCH v2 3/3] mm/vmstat: do not refresh stats for nohz

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Date:   Fri, 02 Jun 2023 15:58:00 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [PATCH v2 3/3] mm/vmstat: do not refresh stats for nohz_full CPUs

The interruption caused by queueing work on nohz_full CPUs 
is undesirable for certain aplications.

Fix by not refreshing per-CPU stats of nohz_full CPUs. 

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

---
v2: opencode schedule_on_each_cpu (Michal Hocko)

Index: linux-vmstat-remote/mm/vmstat.c
===================================================================
--- linux-vmstat-remote.orig/mm/vmstat.c
+++ linux-vmstat-remote/mm/vmstat.c
@@ -1881,8 +1881,13 @@ int vmstat_refresh(struct ctl_table *tab
 		   void *buffer, size_t *lenp, loff_t *ppos)
 {
 	long val;
-	int err;
 	int i;
+	int cpu;
+	struct work_struct __percpu *works;
+
+	works = alloc_percpu(struct work_struct);
+	if (!works)
+		return -ENOMEM;
 
 	/*
 	 * The regular update, every sysctl_stat_interval, may come later
@@ -1896,9 +1901,24 @@ int vmstat_refresh(struct ctl_table *tab
 	 * transiently negative values, report an error here if any of
 	 * the stats is negative, so we know to go looking for imbalance.
 	 */
-	err = schedule_on_each_cpu(refresh_vm_stats);
-	if (err)
-		return err;
+	cpus_read_lock();
+	for_each_online_cpu(cpu) {
+		struct work_struct *work;
+
+		if (cpu_is_isolated(cpu))
+			continue;
+		work = per_cpu_ptr(works, cpu);
+		INIT_WORK(work, refresh_vm_stats);
+		schedule_work_on(cpu, work);
+	}
+
+	for_each_online_cpu(cpu) {
+		if (cpu_is_isolated(cpu))
+			continue;
+		flush_work(per_cpu_ptr(works, cpu));
+	}
+	cpus_read_unlock();
+	free_percpu(works);
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
 		/*
 		 * Skip checking stats known to go negative occasionally.