Commit 176bed1d authored Oct 15, 2015 by Linus Torvalds

vmstat: explicitly schedule per-cpu work on the CPU we need it to run on



The vmstat code uses "schedule_delayed_work_on()" to do the initial
startup of the delayed work on the right CPU, but then once it was
started it would use the non-cpu-specific "schedule_delayed_work()" to
re-schedule it on that CPU.

That just happened to schedule it on the same CPU historically (well, in
almost all situations), but the code _requires_ this work to be per-cpu,
and should say so explicitly rather than depend on the non-cpu-specific
scheduling to schedule on the current CPU.

The timer code is being changed to not be as single-minded in always
running things on the calling CPU.

See also commit 874bbfe6 ("workqueue: make sure delayed work run in
local cpu") that for now maintains the local CPU guarantees just in case
there are other broken users that depended on the accidental behavior.

Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 995e2fe9

mm/vmstat.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -1363,15 +1363,16 @@ static cpumask_var_t cpu_stat_off;

		static void vmstat_update(struct work_struct *w)
		{
		if (refresh_cpu_vm_stats())
		if (refresh_cpu_vm_stats()) {
		/*
		* Counters were updated so we expect more updates
		* to occur in the future. Keep on running the
		* update worker thread.
		*/
		schedule_delayed_work(this_cpu_ptr(&vmstat_work),
		schedule_delayed_work_on(smp_processor_id(),
		this_cpu_ptr(&vmstat_work),
		round_jiffies_relative(sysctl_stat_interval));
		else {
		} else {
		/*
		* We did not update any counters so the app may be in
		* a mode where it does not cause counter updates.

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