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Subject[PATCH 4.16 016/196] mm, slab: reschedule cache_reap() on the same CPU
4.16-stable review patch.  If anyone has any objections, please let me know.


From: Vlastimil Babka <>

commit a9f2a846f0503e7d729f552e3ccfe2279010fe94 upstream.

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.

Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs")
Signed-off-by: Vlastimil Babka <>
Acked-by: Pekka Enberg <>
Acked-by: Christoph Lameter <>
Cc: Joonsoo Kim <>
Cc: David Rientjes <>
Cc: Tejun Heo <>
Cc: Lai Jiangshan <>
Cc: John Stultz <>
Cc: Thomas Gleixner <>
Cc: Stephen Boyd <>
Cc: <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

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

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4074,7 +4074,8 @@ next:
/* 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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