Commit 13583c3d authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
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mm: memcontrol: use special workqueue for creating per-memcg caches

Creating a lot of cgroups at the same time might stall all worker
threads with kmem cache creation works, because kmem cache creation is
done with the slab_mutex held.  The problem was amplified by commits
801faf0d ("mm/slab: lockless decision to grow cache") in case of
SLAB and 81ae6d03 ("mm/slub.c: replace kick_all_cpus_sync() with
synchronize_sched() in kmem_cache_shrink()") in case of SLUB, which
increased the maximal time the slab_mutex can be held.

To prevent that from happening, let's use a special ordered single
threaded workqueue for kmem cache creation.  This shouldn't introduce
any functional changes regarding how kmem caches are created, as the
work function holds the global slab_mutex during its whole runtime
anyway, making it impossible to run more than one work at a time.  By
using a single threaded workqueue, we just avoid creating a thread per
each work.  Ordering is required to avoid a situation when a cgroup's
work is put off indefinitely because there are other cgroups to serve,
in other words to guarantee fairness.


Signed-off-by: default avatarVladimir Davydov <>
Reported-by: default avatarDoug Smythies <>
Acked-by: default avatarMichal Hocko <>
Cc: Christoph Lameter <>
Cc: David Rientjes <>
Cc: Johannes Weiner <>
Cc: Joonsoo Kim <>
Cc: Pekka Enberg <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent c62c38f6
......@@ -2154,6 +2154,8 @@ struct memcg_kmem_cache_create_work {
struct work_struct work;
static struct workqueue_struct *memcg_kmem_cache_create_wq;
static void memcg_kmem_cache_create_func(struct work_struct *w)
struct memcg_kmem_cache_create_work *cw =
......@@ -2185,7 +2187,7 @@ static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
cw->cachep = cachep;
INIT_WORK(&cw->work, memcg_kmem_cache_create_func);
queue_work(memcg_kmem_cache_create_wq, &cw->work);
static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
......@@ -5783,6 +5785,17 @@ static int __init mem_cgroup_init(void)
int cpu, node;
* Kmem cache creation is mostly done with the slab_mutex held,
* so use a special workqueue to avoid stalling all worker
* threads in case lots of cgroups are created simultaneously.
memcg_kmem_cache_create_wq =
alloc_ordered_workqueue("memcg_kmem_cache_create", 0);
hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
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