From: Roman Gushchin <guro@xxxxxx> Subject: mm: memcg/slab: simplify memcg cache creation Because the number of non-root kmem_caches doesn't depend on the number of memory cgroups anymore and is generally not very big, there is no more need for a dedicated workqueue. Also, as there is no more need to pass any arguments to the memcg_create_kmem_cache() except the root kmem_cache, it's possible to just embed the work structure into the kmem_cache and avoid the dynamic allocation of the work structure. This will also simplify the synchronization: for each root kmem_cache there is only one work. So there will be no more concurrent attempts to create a non-root kmem_cache for a root kmem_cache: the second and all following attempts to queue the work will fail. On the kmem_cache destruction path there is no more need to call the expensive flush_workqueue() and wait for all pending works to be finished. Instead, cancel_work_sync() can be used to cancel/wait for only one work. Link: http://lkml.kernel.org/r/20200623174037.3951353-14-guro@xxxxxx Signed-off-by: Roman Gushchin <guro@xxxxxx> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/memcontrol.h | 1 mm/memcontrol.c | 48 ----------------------------------- mm/slab.h | 2 + mm/slab_common.c | 22 ++++++++-------- 4 files changed, 15 insertions(+), 58 deletions(-) --- a/include/linux/memcontrol.h~mm-memcg-slab-simplify-memcg-cache-creation +++ a/include/linux/memcontrol.h @@ -1418,7 +1418,6 @@ int obj_cgroup_charge(struct obj_cgroup void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size); extern struct static_key_false memcg_kmem_enabled_key; -extern struct workqueue_struct *memcg_kmem_cache_wq; extern int memcg_nr_cache_ids; void memcg_get_cache_ids(void); --- a/mm/memcontrol.c~mm-memcg-slab-simplify-memcg-cache-creation +++ a/mm/memcontrol.c @@ -399,8 +399,6 @@ void memcg_put_cache_ids(void) */ DEFINE_STATIC_KEY_FALSE(memcg_kmem_enabled_key); EXPORT_SYMBOL(memcg_kmem_enabled_key); - -struct workqueue_struct *memcg_kmem_cache_wq; #endif static int memcg_shrinker_map_size; @@ -2902,39 +2900,6 @@ static void memcg_free_cache_id(int id) ida_simple_remove(&memcg_cache_ida, id); } -struct memcg_kmem_cache_create_work { - struct kmem_cache *cachep; - struct work_struct work; -}; - -static void memcg_kmem_cache_create_func(struct work_struct *w) -{ - struct memcg_kmem_cache_create_work *cw = - container_of(w, struct memcg_kmem_cache_create_work, work); - struct kmem_cache *cachep = cw->cachep; - - memcg_create_kmem_cache(cachep); - - kfree(cw); -} - -/* - * Enqueue the creation of a per-memcg kmem_cache. - */ -static void memcg_schedule_kmem_cache_create(struct kmem_cache *cachep) -{ - struct memcg_kmem_cache_create_work *cw; - - cw = kmalloc(sizeof(*cw), GFP_NOWAIT | __GFP_NOWARN); - if (!cw) - return; - - cw->cachep = cachep; - INIT_WORK(&cw->work, memcg_kmem_cache_create_func); - - queue_work(memcg_kmem_cache_wq, &cw->work); -} - /** * memcg_kmem_get_cache: select memcg or root cache for allocation * @cachep: the original global kmem cache @@ -2951,7 +2916,7 @@ struct kmem_cache *memcg_kmem_get_cache( memcg_cachep = READ_ONCE(cachep->memcg_params.memcg_cache); if (unlikely(!memcg_cachep)) { - memcg_schedule_kmem_cache_create(cachep); + queue_work(system_wq, &cachep->memcg_params.work); return cachep; } @@ -7022,17 +6987,6 @@ static int __init mem_cgroup_init(void) { int cpu, node; -#ifdef CONFIG_MEMCG_KMEM - /* - * Kmem cache creation is mostly done with the slab_mutex held, - * so use a workqueue with limited concurrency to avoid stalling - * all worker threads in case lots of cgroups are created and - * destroyed simultaneously. - */ - memcg_kmem_cache_wq = alloc_workqueue("memcg_kmem_cache", 0, 1); - BUG_ON(!memcg_kmem_cache_wq); -#endif - cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL, memcg_hotplug_cpu_dead); --- a/mm/slab_common.c~mm-memcg-slab-simplify-memcg-cache-creation +++ a/mm/slab_common.c @@ -134,10 +134,18 @@ int __kmem_cache_alloc_bulk(struct kmem_ LIST_HEAD(slab_root_caches); +static void memcg_kmem_cache_create_func(struct work_struct *work) +{ + struct kmem_cache *cachep = container_of(work, struct kmem_cache, + memcg_params.work); + memcg_create_kmem_cache(cachep); +} + void slab_init_memcg_params(struct kmem_cache *s) { s->memcg_params.root_cache = NULL; s->memcg_params.memcg_cache = NULL; + INIT_WORK(&s->memcg_params.work, memcg_kmem_cache_create_func); } static void init_memcg_params(struct kmem_cache *s, @@ -586,15 +594,9 @@ static int shutdown_memcg_caches(struct return 0; } -static void flush_memcg_workqueue(struct kmem_cache *s) +static void cancel_memcg_cache_creation(struct kmem_cache *s) { - /* - * SLAB and SLUB create memcg kmem_caches through workqueue and SLUB - * deactivates the memcg kmem_caches through workqueue. Make sure all - * previous workitems on workqueue are processed. - */ - if (likely(memcg_kmem_cache_wq)) - flush_workqueue(memcg_kmem_cache_wq); + cancel_work_sync(&s->memcg_params.work); } #else static inline int shutdown_memcg_caches(struct kmem_cache *s) @@ -602,7 +604,7 @@ static inline int shutdown_memcg_caches( return 0; } -static inline void flush_memcg_workqueue(struct kmem_cache *s) +static inline void cancel_memcg_cache_creation(struct kmem_cache *s) { } #endif /* CONFIG_MEMCG_KMEM */ @@ -621,7 +623,7 @@ void kmem_cache_destroy(struct kmem_cach if (unlikely(!s)) return; - flush_memcg_workqueue(s); + cancel_memcg_cache_creation(s); get_online_cpus(); get_online_mems(); --- a/mm/slab.h~mm-memcg-slab-simplify-memcg-cache-creation +++ a/mm/slab.h @@ -45,12 +45,14 @@ struct kmem_cache { * @memcg_cache: pointer to memcg kmem cache, used by all non-root memory * cgroups. * @root_caches_node: list node for slab_root_caches list. + * @work: work struct used to create the non-root cache. */ struct memcg_cache_params { struct kmem_cache *root_cache; struct kmem_cache *memcg_cache; struct list_head __root_caches_node; + struct work_struct work; }; #endif /* CONFIG_SLOB */ _
