LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Marcelo Tosatti <mtosatti@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Nitesh Lal <nilal@redhat.com>,
	Nicolas Saenz Julienne <nsaenzju@redhat.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Christoph Lameter <cl@linux.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Alex Belits <abelits@belits.com>, Peter Xu <peterx@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>
Subject: [patch 2/4] task isolation: sync vmstats on return to userspace
Date: Fri, 30 Jul 2021 17:18:29 -0300	[thread overview]
Message-ID: <20210730202010.270885685@fuller.cnet> (raw)
In-Reply-To: <20210730201827.269106165@fuller.cnet>

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:

1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats.
2) app runs mlock, which increases counters for mlock'ed pages.
3) start -RT loop

Since refresh_cpu_vm_stats from nohz_full logic can happen _before_
the mlock, vmstat shepherd can restart vmstat worker thread on
the CPU in question.

To fix this, use the task isolation prctl interface to quiesce 
deferred actions when returning to userspace.

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

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
@@ -32,8 +32,20 @@ int prctl_task_isolation_ctrl_get(unsign
 int prctl_task_isolation_ctrl_set(unsigned long arg2, unsigned long arg3,
 				  unsigned long arg4, unsigned long arg5);
 
+void __isolation_exit_to_user_mode_prepare(void);
+
+static inline void isolation_exit_to_user_mode_prepare(void)
+{
+	if (current->isol_info != NULL)
+		__isolation_exit_to_user_mode_prepare();
+}
+
 #else
 
+static void isolation_exit_to_user_mode_prepare(void)
+{
+}
+
 static inline void tsk_isol_exit(struct task_struct *tsk)
 {
 }
Index: linux-2.6/include/linux/vmstat.h
===================================================================
--- linux-2.6.orig/include/linux/vmstat.h
+++ linux-2.6/include/linux/vmstat.h
@@ -21,6 +21,14 @@ int sysctl_vm_numa_stat_handler(struct c
 		void *buffer, size_t *length, loff_t *ppos);
 #endif
 
+#ifdef CONFIG_SMP
+void sync_vmstat(void);
+#else
+static inline void sync_vmstat(void)
+{
+}
+#endif
+
 struct reclaim_stat {
 	unsigned nr_dirty;
 	unsigned nr_unqueued_dirty;
Index: linux-2.6/kernel/entry/common.c
===================================================================
--- linux-2.6.orig/kernel/entry/common.c
+++ linux-2.6/kernel/entry/common.c
@@ -6,6 +6,7 @@
 #include <linux/livepatch.h>
 #include <linux/audit.h>
 #include <linux/tick.h>
+#include <linux/task_isolation.h>
 
 #include "common.h"
 
@@ -287,6 +288,7 @@ static void syscall_exit_to_user_mode_pr
 static __always_inline void __syscall_exit_to_user_mode_work(struct pt_regs *regs)
 {
 	syscall_exit_to_user_mode_prepare(regs);
+	isolation_exit_to_user_mode_prepare();
 	local_irq_disable_exit_to_user();
 	exit_to_user_mode_prepare(regs);
 }
Index: linux-2.6/kernel/task_isolation.c
===================================================================
--- linux-2.6.orig/kernel/task_isolation.c
+++ linux-2.6/kernel/task_isolation.c
@@ -17,6 +17,8 @@
 #include <linux/string.h>
 #include <linux/sysfs.h>
 #include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/vmstat.h>
 
 static unsigned long default_quiesce_mask;
 
@@ -145,6 +147,17 @@ int prctl_task_isolation_ctrl_get(unsign
 	return current->isol_info->active_mask;
 }
 
+void __isolation_exit_to_user_mode_prepare(void)
+{
+	struct isol_info *i = current->isol_info;
+
+	if (i->active_mask != ISOL_F_QUIESCE)
+		return;
+
+	if (i->quiesce_mask & ISOL_F_QUIESCE_VMSTATS)
+		sync_vmstat();
+}
+
 struct qoptions {
 	unsigned long mask;
 	char *name;
Index: linux-2.6/mm/vmstat.c
===================================================================
--- linux-2.6.orig/mm/vmstat.c
+++ linux-2.6/mm/vmstat.c
@@ -1964,6 +1964,27 @@ static void vmstat_shepherd(struct work_
 		round_jiffies_relative(sysctl_stat_interval));
 }
 
+void sync_vmstat(void)
+{
+	int cpu;
+
+	cpu = get_cpu();
+
+	refresh_cpu_vm_stats(false);
+	put_cpu();
+
+	/*
+	 * If task is migrated to another CPU between put_cpu
+	 * and cancel_delayed_work_sync, the code below might
+	 * cancel vmstat_update work for a different cpu
+	 * (than the one from which the vmstats were flushed).
+	 *
+	 * However, vmstat shepherd will re-enable it later,
+	 * so its harmless.
+	 */
+	cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
+}
+
 static void __init start_shepherd_timer(void)
 {
 	int cpu;



  parent reply	other threads:[~2021-07-30 20:21 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30 20:18 [patch 0/4] extensible prctl task isolation interface and vmstat sync (v2) Marcelo Tosatti
2021-07-30 20:18 ` [patch 1/4] add basic task isolation prctl interface Marcelo Tosatti
     [not found]   ` <CAFki+Lnf0cs62Se0aPubzYxP9wh7xjMXn7RXEPvrmtBdYBrsow@mail.gmail.com>
2021-07-31  0:49     ` Marcelo Tosatti
2021-07-31  7:47   ` kernel test robot
     [not found]   ` <CAFki+LkQVQOe+5aNEKWDvLdnjWjxzKWOiqOvBZzeuPWX+G=XgA@mail.gmail.com>
2021-08-02 14:16     ` Marcelo Tosatti
2021-07-30 20:18 ` Marcelo Tosatti [this message]
2021-08-03 15:13   ` [patch 2/4] task isolation: sync vmstats on return to userspace nsaenzju
2021-08-03 16:44     ` Marcelo Tosatti
2021-07-30 20:18 ` [patch 3/4] mm: vmstat: move need_update Marcelo Tosatti
2021-07-30 20:18 ` [patch 4/4] mm: vmstat_refresh: avoid queueing work item if cpu stats are clean Marcelo Tosatti
2021-08-07  2:47   ` Nitesh Lal
2021-08-09 17:34     ` Marcelo Tosatti
2021-08-09 19:13       ` Nitesh Lal
2021-08-10 16:40 ` [patch 0/4] extensible prctl task isolation interface and vmstat sync (v2) Thomas Gleixner
2021-08-10 18:37   ` Marcelo Tosatti
2021-08-10 19:15     ` Marcelo Tosatti
  -- strict thread matches above, loose matches on Subject: below --
2021-07-27 10:38 [patch 0/4] prctl task isolation interface and vmstat sync Marcelo Tosatti
2021-07-27 10:38 ` [patch 2/4] task isolation: sync vmstats on return to userspace Marcelo Tosatti

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210730202010.270885685@fuller.cnet \
    --to=mtosatti@redhat.com \
    --cc=abelits@belits.com \
    --cc=cl@linux.com \
    --cc=frederic@kernel.org \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=nilal@redhat.com \
    --cc=nsaenzju@redhat.com \
    --cc=peterx@redhat.com \
    --cc=peterz@infradead.org \
    --subject='Re: [patch 2/4] task isolation: sync vmstats on return to userspace' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).