From: Vlastimil Babka vbabka@suse.cz Subject: mm, slab: reschedule cache_reap() on the same CPU

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.

Link: http://lkml.kernel.org/r/20180411070007.32225-1-vbabka@suse.cz Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs") Signed-off-by: Vlastimil Babka vbabka@suse.cz Acked-by: Pekka Enberg penberg@kernel.org Acked-by: Christoph Lameter cl@linux.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Cc: David Rientjes rientjes@google.com Cc: Tejun Heo tj@kernel.org Cc: Lai Jiangshan jiangshanlai@gmail.com Cc: John Stultz john.stultz@linaro.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Stephen Boyd sboyd@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/slab.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN mm/slab.c~mm-slab-reschedule-cache_reap-on-the-same-cpu mm/slab.c --- a/mm/slab.c~mm-slab-reschedule-cache_reap-on-the-same-cpu +++ a/mm/slab.c @@ -4086,7 +4086,8 @@ next: 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) _