From: Vlastimil Babka <vbabka@xxxxxxx>
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@xxxxxxx
Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs")
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Pekka Enberg <penberg@xxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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)
_
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