On Wed, Apr 11, 2018 at 09:00:07AM +0200, Vlastimil Babka wrote: > cache_reap() is initially scheduled in start_cpu_timer() via > schedule_delayed_work_on(). But then the next iterations are scheduled via > schedule_delayed_work(), i.e. using WORK_CPU_UNBOUND. > > Thus since commit ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on > wq_unbound_cpumask CPUs") there is no guarantee the future iterations will run > on the originally intended cpu, although it's still preferred. I was able to > demonstrate this with /sys/module/workqueue/parameters/debug_force_rr_cpu. > IIUC, it may also happen due to migrating timers in nohz context. As a result, > some cpu's would be calling cache_reap() more frequently and others never. > > This patch uses schedule_delayed_work_on() with the current cpu when > scheduling > the next iteration.
Could you write down part about "so what's the user effect on some condition?". It would really help to pick up the patch. > > Signed-off-by: Vlastimil Babka <vba...@suse.cz> > Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on > wq_unbound_cpumask CPUs") > CC: <sta...@vger.kernel.org> > Cc: Joonsoo Kim <iamjoonsoo....@lge.com> > Cc: David Rientjes <rient...@google.com> > Cc: Pekka Enberg <penb...@kernel.org> > Cc: Christoph Lameter <c...@linux.com> > Cc: Tejun Heo <t...@kernel.org> > Cc: Lai Jiangshan <jiangshan...@gmail.com> > Cc: John Stultz <john.stu...@linaro.org> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Stephen Boyd <sb...@kernel.org> > --- > mm/slab.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/slab.c b/mm/slab.c > index 9095c3945425..a76006aae857 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -4074,7 +4074,8 @@ static void cache_reap(struct work_struct *w) > next_reap_node(); > out: > /* Set up the next iteration */ > - schedule_delayed_work(work, round_jiffies_relative(REAPTIMEOUT_AC)); > + schedule_delayed_work_on(smp_processor_id(), work, > + round_jiffies_relative(REAPTIMEOUT_AC)); > } > > void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo) > -- > 2.16.3 >