linux-kernel - [PATCH v8 3/5] mm/vmstat: Do not queue vmstat

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Date:   Sat, 24 Sep 2022 16:22:25 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     frederic@...nel.org, mtosatti@...hat.com
Cc:     cl@...ux.com, tglx@...utronix.de, mingo@...nel.org,
        peterz@...radead.org, pauld@...hat.com, neelx@...hat.com,
        oleksandr@...alenko.name, atomlin@...mlin.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH v8 3/5] mm/vmstat: Do not queue vmstat_update if tick is stopped

From: Marcelo Tosatti <mtosatti@...hat.com>

>From the vmstat shepherd, for CPUs that have the tick stopped, do not
queue local work to flush the per-CPU vmstats, since in that case the
flush is performed on return to userspace or when entering idle. Also
cancel any delayed work on the local CPU, when entering idle on nohz
full CPUs. Per-CPU pages can be freed remotely from housekeeping CPUs.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
---
 mm/vmstat.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 472175642bd9..3b9a497965b4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -29,6 +29,7 @@
 #include <linux/page_ext.h>
 #include <linux/page_owner.h>
 #include <linux/migrate.h>
+#include <linux/tick.h>
 
 #include "internal.h"
 
@@ -1990,19 +1991,23 @@ static void vmstat_update(struct work_struct *w)
  */
 void quiet_vmstat(void)
 {
+	struct delayed_work *dw;
+
 	if (system_state != SYSTEM_RUNNING)
 		return;
 
 	if (!is_vmstat_dirty())
 		return;
 
+	refresh_cpu_vm_stats(false);
+
 	/*
-	 * Just refresh counters and do not care about the pending delayed
-	 * vmstat_update. It doesn't fire that often to matter and canceling
-	 * it would be too expensive from this path.
-	 * vmstat_shepherd will take care about that for us.
+	 * If the tick is stopped, cancel any delayed work to avoid
+	 * interruptions to this CPU in the future.
 	 */
-	refresh_cpu_vm_stats(false);
+	dw = &per_cpu(vmstat_work, smp_processor_id());
+	if (delayed_work_pending(dw) && tick_nohz_tick_stopped())
+		cancel_delayed_work(dw);
 }
 
 /*
@@ -2024,6 +2029,9 @@ static void vmstat_shepherd(struct work_struct *w)
 	for_each_online_cpu(cpu) {
 		struct delayed_work *dw = &per_cpu(vmstat_work, cpu);
 
+		if (tick_nohz_tick_stopped_cpu(cpu))
+			continue;
+
 		if (!delayed_work_pending(dw) && per_cpu(vmstat_dirty, cpu))
 			queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0);
 
-- 
2.37.1