Commit 7b8da4c7 authored by Christoph Lameter's avatar Christoph Lameter Committed by Linus Torvalds
Browse files

vmstat: get rid of the ugly cpu_stat_off variable 

The cpu_stat_off variable is unecessary since we can check if a
workqueue request is pending otherwise.  Removal of cpu_stat_off makes
it pretty easy for the vmstat shepherd to ensure that the proper things
happen.

Removing the state also removes all races related to it.  Should a
workqueue not be scheduled as needed for vmstat_update then the shepherd
will notice and schedule it as needed.  Should a workqueue be
unecessarily scheduled then the vmstat updater will disable it.

[akpm@linux-foundation.org: fix indentation, per Michal]
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1605061306460.17934@east.gentwo.org


Signed-off-by: default avatarChristoph Lameter <cl@linux.com>
Cc: Tejun Heo <htejun@gmail.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 51038171

mm/vmstat.c

+10 −41
Original line number Diff line number Diff line
@@ -1352,7 +1352,6 @@ static const struct file_operations proc_vmstat_file_operations = { 
static struct workqueue_struct *vmstat_wq;

static DEFINE_PER_CPU(struct delayed_work, vmstat_work);

int sysctl_stat_interval __read_mostly = HZ;

static cpumask_var_t cpu_stat_off;



#ifdef CONFIG_PROC_FS

static void refresh_vm_stats(struct work_struct *work)
@@ -1421,25 +1420,11 @@ static void vmstat_update(struct work_struct *w) 
		 * Counters were updated so we expect more updates

		 * to occur in the future. Keep on running the

		 * update worker thread.

		 * If we were marked on cpu_stat_off clear the flag

		 * so that vmstat_shepherd doesn't schedule us again.

		 */

		if (!cpumask_test_and_clear_cpu(smp_processor_id(),

						cpu_stat_off)) {

		queue_delayed_work_on(smp_processor_id(), vmstat_wq,

				this_cpu_ptr(&vmstat_work),

				round_jiffies_relative(sysctl_stat_interval));

	}

	} else {

		/*

		 * We did not update any counters so the app may be in

		 * a mode where it does not cause counter updates.

		 * We may be uselessly running vmstat_update.

		 * Defer the checking for differentials to the

		 * shepherd thread on a different processor.

		 */

		cpumask_set_cpu(smp_processor_id(), cpu_stat_off);

	}

}



/*
@@ -1470,16 +1455,17 @@ static bool need_update(int cpu) 
	return false;

}



/*

 * Switch off vmstat processing and then fold all the remaining differentials

 * until the diffs stay at zero. The function is used by NOHZ and can only be

 * invoked when tick processing is not active.

 */

void quiet_vmstat(void)

{

	if (system_state != SYSTEM_RUNNING)

		return;



	/*

	 * If we are already in hands of the shepherd then there

	 * is nothing for us to do here.

	 */

	if (cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))

	if (!delayed_work_pending(this_cpu_ptr(&vmstat_work)))

		return;



	if (!need_update(smp_processor_id()))
@@ -1494,7 +1480,6 @@ void quiet_vmstat(void) 
	refresh_cpu_vm_stats(false);

}





/*

 * Shepherd worker thread that checks the

 * differentials of processors that have their worker
@@ -1511,20 +1496,11 @@ static void vmstat_shepherd(struct work_struct *w) 


	get_online_cpus();

	/* Check processors whose vmstat worker threads have been disabled */

	for_each_cpu(cpu, cpu_stat_off) {

	for_each_online_cpu(cpu) {

		struct delayed_work *dw = &per_cpu(vmstat_work, cpu);



		if (need_update(cpu)) {

			if (cpumask_test_and_clear_cpu(cpu, cpu_stat_off))

		if (!delayed_work_pending(dw) && need_update(cpu))

			queue_delayed_work_on(cpu, vmstat_wq, dw, 0);

		} else {

			/*

			 * Cancel the work if quiet_vmstat has put this

			 * cpu on cpu_stat_off because the work item might

			 * be still scheduled

			 */

			cancel_delayed_work(dw);

		}

	}

	put_online_cpus();
@@ -1540,10 +1516,6 @@ static void __init start_shepherd_timer(void) 
		INIT_DEFERRABLE_WORK(per_cpu_ptr(&vmstat_work, cpu),

			vmstat_update);



	if (!alloc_cpumask_var(&cpu_stat_off, GFP_KERNEL))

		BUG();

	cpumask_copy(cpu_stat_off, cpu_online_mask);



	vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);

	schedule_delayed_work(&shepherd,

		round_jiffies_relative(sysctl_stat_interval));
@@ -1578,16 +1550,13 @@ static int vmstat_cpuup_callback(struct notifier_block *nfb, 
	case CPU_ONLINE_FROZEN:

		refresh_zone_stat_thresholds();

		node_set_state(cpu_to_node(cpu), N_CPU);

		cpumask_set_cpu(cpu, cpu_stat_off);

		break;

	case CPU_DOWN_PREPARE:

	case CPU_DOWN_PREPARE_FROZEN:

		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));

		cpumask_clear_cpu(cpu, cpu_stat_off);

		break;

	case CPU_DOWN_FAILED:

	case CPU_DOWN_FAILED_FROZEN:

		cpumask_set_cpu(cpu, cpu_stat_off);

		break;

	case CPU_DEAD:

	case CPU_DEAD_FROZEN:

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