[PATCH 4.9 54/69] mm: memcontrol: use special workqueue for creating per-memcg caches

Greg Kroah-Hartman
2017-04-19T14:50:52Z

From: Vladimir Davydov <vdavydov.dev@gmail.com>

commit 13583c3d3224508582ec03d881d0b68dd3ee8e10 upstream.

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
801faf0db894 ("mm/slab: lockless decision to grow cache") in case of
SLAB and 81ae6d03952c ("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.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=172981
Link: http://lkml.kernel.org/r/20161004131417.GC1862@esperanza
Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reported-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/memcontrol.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2152,6 +2152,8 @@ 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 =
@@ -2183,7 +2185,7 @@ static void __memcg_schedule_kmem_cache_
cw->cachep = cachep;
INIT_WORK(&cw->work, memcg_kmem_cache_create_func);

- schedule_work(&cw->work);
+ queue_work(memcg_kmem_cache_create_wq, &cw->work);
}

static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
@@ -5786,6 +5788,17 @@ static int __init mem_cgroup_init(void)
{
int cpu, node;

+#ifndef CONFIG_SLOB
+ /*
+ * 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);
+ BUG_ON(!memcg_kmem_cache_create_wq);
+#endif
+
hotcpu_notifier(memcg_cpu_hotplug_callback, 0);

for_each_possible_cpu(cpu)