The patch titled
Subject: mm: memcontrol: use special workqueue for creating per-memcg caches
has been added to the -mm tree. Its filename is
mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches.patch
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------------------------------------------------------
From: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Subject: 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 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@xxxxxxxxx>
Reported-by: Doug Smythies <dsmythies@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff -puN mm/memcontrol.c~mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches
+++ a/mm/memcontrol.c
@@ -2145,6 +2145,8 @@ 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 =
@@ -2176,7 +2178,7 @@ 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,
@@ -5774,6 +5776,17 @@ 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)
_
Patches currently in -mm which might be from vdavydov.dev@xxxxxxxxx are
mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches.patch
slub-move-synchronize_sched-out-of-slab_mutex-on-shrink.patch
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