linux-kernel - [patch v6 07/10] task isolation: enable return to userspace processing

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Message-ID: <20211112122641.953894539@fedora.localdomain>
Date:   Fri, 12 Nov 2021 09:16:49 -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 v6 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: <20211112121642.693790927@...ora.localdomain>
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 isol_info {
 	/* Which features have been configured */
 	u64 conf_mask;
@@ -51,7 +54,24 @@ void isolation_exit_to_user_mode(void);
 
 static inline int task_isol_has_work(void)
 {
-	return 0;
+	int cpu, ret;
+	struct isol_info *i;
+
+	if (likely(current->isol_info == NULL))
+		return 0;
+
+	i = current->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;
 }
 
 #else
Index: linux-2.6/kernel/task_isolation.c
===================================================================
--- linux-2.6.orig/kernel/task_isolation.c
+++ linux-2.6/kernel/task_isolation.c
@@ -23,6 +23,13 @@
 
 void __tsk_isol_exit(struct task_struct *tsk)
 {
+	struct isol_info *i;
+
+	i = tsk->isol_info;
+	if (!i)
+		return;
+
+	static_key_slow_dec(&vmstat_sync_enabled);
 }
 
 void __tsk_isol_free(struct task_struct *tsk)
@@ -41,6 +48,12 @@ static struct isol_info *tsk_isol_alloc_
 	if (unlikely(!info))
 		return ERR_PTR(-ENOMEM);
 
+	preempt_disable();
+	init_sync_vmstat();
+	preempt_enable();
+
+	static_key_slow_inc(&vmstat_sync_enabled);
+
 	return info;
 }