From: Vladimir Davydov Date: Sat, 1 Oct 2016 13:39:09 +0000 (+0300) Subject: mm: memcontrol: use special workqueue for creating per-memcg caches X-Git-Tag: archive/raspbian/4.9.13-1+rpi1~11^2~64 X-Git-Url: https://dgit.raspbian.org/%22http:/www.example.com/cgi/%22https://%22Program/%22http:/www.example.com/cgi/%22https:/%22Program?a=commitdiff_plain;h=63ebbafad588328acfdab300ca9115d3deb5da2b;p=linux-4.9.git 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 Signed-off-by: Vladimir Davydov Reported-by: Doug Smythies Cc: Christoph Lameter Cc: David Rientjes Cc: Johannes Weiner Cc: Joonsoo Kim Cc: Michal Hocko Cc: Pekka Enberg Acked-by: Michal Hocko Gbp-Pq: Topic bugfix/all Gbp-Pq: Name mm-memcontrol-use-special-workqueue-for-creating-per-memcg-caches.patch --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4c6ade54d833..44fb1e80701a 100644 --- 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_create(struct mem_cgroup *memcg, 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, @@ -5781,6 +5783,17 @@ 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)