linux-kernel - [patch v9 07/10] task isolation: enable return to userspace processing

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Date:   Thu, 27 Jan 2022 14:23:26 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [patch v9 07/10] task isolation: enable return to userspace processing

The logic to disable vmstat worker thread, when entering
nohz full, does not cover all scenarios. For example, it is possible
for the following to happen:
References: <20220127172319.428529308@...ler.cnet>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8

Enable processing of pending task isolation work if per-CPU vmstats
are out of sync with global vmstats.

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

---
 include/linux/task_isolation.h |   22 +++++++++++++++++++++-
 kernel/task_isolation.c        |   13 +++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

Index: linux-2.6/include/linux/task_isolation.h
===================================================================
--- linux-2.6.orig/include/linux/task_isolation.h
+++ linux-2.6/include/linux/task_isolation.h
@@ -5,6 +5,9 @@
 
 #ifdef CONFIG_CPU_ISOLATION
 
+#include <linux/vmstat.h>
+#include <uapi/linux/prctl.h>
+
 struct task_isol_info {
 	/* Which features have been configured */
 	u64 conf_mask;
@@ -110,7 +113,24 @@ static inline int prctl_task_isol_activa
 
 static inline int task_isol_has_work(void)
 {
-	return 0;
+	int cpu, ret;
+	struct isol_info *i;
+
+	if (likely(current->task_isol_info == NULL))
+		return 0;
+
+	i = current->task_isol_info;
+	if (i->active_mask != ISOL_F_QUIESCE)
+		return 0;
+
+	if (!(i->quiesce_mask & ISOL_F_QUIESCE_VMSTATS))
+		return 0;
+
+	cpu = get_cpu();
+	ret = per_cpu(vmstat_dirty, cpu);
+	put_cpu();
+
+	return ret;
 }
 
 #endif /* CONFIG_CPU_ISOLATION */
Index: linux-2.6/kernel/task_isolation.c
===================================================================
--- linux-2.6.orig/kernel/task_isolation.c
+++ linux-2.6/kernel/task_isolation.c
@@ -10,7 +10,6 @@
  */
 
 #include <linux/sched.h>
-#include <linux/task_isolation.h>
 #include <linux/prctl.h>
 #include <linux/slab.h>
 #include <linux/kobject.h>
@@ -20,9 +19,17 @@
 #include <linux/sched/task.h>
 #include <linux/mm.h>
 #include <linux/vmstat.h>
+#include <linux/task_isolation.h>
 
 void __task_isol_exit(struct task_struct *tsk)
 {
+	struct task_isol_info *i;
+
+	i = tsk->task_isol_info;
+	if (!i)
+		return;
+
+	static_key_slow_dec(&vmstat_sync_enabled);
 }
 
 void __task_isol_free(struct task_struct *tsk)
@@ -41,6 +48,12 @@ static struct task_isol_info *task_isol_
 	if (unlikely(!info))
 		return ERR_PTR(-ENOMEM);
 
+	preempt_disable();
+	init_sync_vmstat();
+	preempt_enable();
+
+	static_key_slow_inc(&vmstat_sync_enabled);
+
 	return info;
 }