Re: [PATCH v3 2/7] mm: generalize postponed non-root kmem_cache deactivation

Shakeel Butt
2019-05-11T00:33:15Z

Date: Wed, May 8, 2019 at 1:30 PM
To: Andrew Morton, Shakeel Butt
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
<kernel-team@fb.com>, Johannes Weiner, Michal Hocko, Rik van Riel,
Christoph Lameter, Vladimir Davydov, <cgroups@vger.kernel.org>, Roman
Gushchin

> Currently SLUB uses a work scheduled after an RCU grace period
> to deactivate a non-root kmem_cache. This mechanism can be reused
> for kmem_caches reparenting, but requires some generalization.
>
> Let's decouple all infrastructure (rcu callback, work callback)
> from the SLUB-specific code, so it can be used with SLAB as well.
>
> Also, let's rename some functions to make the code look simpler.
> All SLAB/SLUB-specific functions start with "__". Remove "deact_"
> prefix from the corresponding struct fields.
>
> Here is the graph of a new calling scheme:
> kmemcg_cache_deactivate()
> __kmemcg_cache_deactivate() SLAB/SLUB-specific
> kmemcg_schedule_work_after_rcu() rcu
> kmemcg_after_rcu_workfn() work
> kmemcg_cache_deactivate_after_rcu()
> __kmemcg_cache_deactivate_after_rcu() SLAB/SLUB-specific
>
> instead of:
> __kmemcg_cache_deactivate() SLAB/SLUB-specific
> slab_deactivate_memcg_cache_rcu_sched() SLUB-only
> kmemcg_deactivate_rcufn SLUB-only, rcu
> kmemcg_deactivate_workfn SLUB-only, work
> kmemcg_cache_deact_after_rcu() SLUB-only
>
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

> ---
> include/linux/slab.h | 6 ++---
> mm/slab.c | 4 +++
> mm/slab.h | 3 ++-
> mm/slab_common.c | 62 ++++++++++++++++++++------------------------
> mm/slub.c | 8 +-----
> 5 files changed, 38 insertions(+), 45 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 9449b19c5f10..47923c173f30 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -642,10 +642,10 @@ struct memcg_cache_params {
> struct list_head children_node;
> struct list_head kmem_caches_node;
>
> - void (*deact_fn)(struct kmem_cache *);
> + void (*work_fn)(struct kmem_cache *);
> union {
> - struct rcu_head deact_rcu_head;
> - struct work_struct deact_work;
> + struct rcu_head rcu_head;
> + struct work_struct work;
> };
> };
> };
> diff --git a/mm/slab.c b/mm/slab.c
> index f6eff59e018e..83000e46b870 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2281,6 +2281,10 @@ void __kmemcg_cache_deactivate(struct kmem_cache *cachep)
> {
> __kmem_cache_shrink(cachep);
> }
> +
> +void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
> +{
> +}
> #endif
>
> int __kmem_cache_shutdown(struct kmem_cache *cachep)
> diff --git a/mm/slab.h b/mm/slab.h
> index 6a562ca72bca..4a261c97c138 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -172,6 +172,7 @@ int __kmem_cache_shutdown(struct kmem_cache *);
> void __kmem_cache_release(struct kmem_cache *);
> int __kmem_cache_shrink(struct kmem_cache *);
> void __kmemcg_cache_deactivate(struct kmem_cache *s);
> +void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s);
> void slab_kmem_cache_release(struct kmem_cache *);
>
> struct seq_file;
> @@ -291,7 +292,7 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
> extern void slab_init_memcg_params(struct kmem_cache *);
> extern void memcg_link_cache(struct kmem_cache *s, struct mem_cgroup *memcg);
> extern void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
> - void (*deact_fn)(struct kmem_cache *));
> + void (*work_fn)(struct kmem_cache *));
>
> #else /* CONFIG_MEMCG_KMEM */
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 6e00bdf8618d..4e5b4292a763 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -691,17 +691,18 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
> put_online_cpus();
> }
>
> -static void kmemcg_deactivate_workfn(struct work_struct *work)
> +static void kmemcg_after_rcu_workfn(struct work_struct *work)
> {
> struct kmem_cache *s = container_of(work, struct kmem_cache,
> - memcg_params.deact_work);
> + memcg_params.work);
>
> get_online_cpus();
> get_online_mems();
>
> mutex_lock(&slab_mutex);
>
> - s->memcg_params.deact_fn(s);
> + s->memcg_params.work_fn(s);
> + s->memcg_params.work_fn = NULL;
>
> mutex_unlock(&slab_mutex);
>
> @@ -712,37 +713,28 @@ static void kmemcg_deactivate_workfn(struct work_struct *work)
> css_put(&s->memcg_params.memcg->css);
> }
>
> -static void kmemcg_deactivate_rcufn(struct rcu_head *head)
> +/*
> + * We need to grab blocking locks. Bounce to ->work. The
> + * work item shares the space with the RCU head and can't be
> + * initialized eariler.
> +*/
> +static void kmemcg_schedule_work_after_rcu(struct rcu_head *head)
> {
> struct kmem_cache *s = container_of(head, struct kmem_cache,
> - memcg_params.deact_rcu_head);
> + memcg_params.rcu_head);
>
> - /*
> - * We need to grab blocking locks. Bounce to ->deact_work. The
> - * work item shares the space with the RCU head and can't be
> - * initialized eariler.
> - */
> - INIT_WORK(&s->memcg_params.deact_work, kmemcg_deactivate_workfn);
> - queue_work(memcg_kmem_cache_wq, &s->memcg_params.deact_work);
> + INIT_WORK(&s->memcg_params.work, kmemcg_after_rcu_workfn);
> + queue_work(memcg_kmem_cache_wq, &s->memcg_params.work);
> }
>
> -/**
> - * slab_deactivate_memcg_cache_rcu_sched - schedule deactivation after a
> - * sched RCU grace period
> - * @s: target kmem_cache
> - * @deact_fn: deactivation function to call
> - *
> - * Schedule @deact_fn to be invoked with online cpus, mems and slab_mutex
> - * held after a sched RCU grace period. The slab is guaranteed to stay
> - * alive until @deact_fn is finished. This is to be used from
> - * __kmemcg_cache_deactivate().
> - */
> -void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
> - void (*deact_fn)(struct kmem_cache *))
> +static void kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
> {
> - if (WARN_ON_ONCE(is_root_cache(s)) ||
> - WARN_ON_ONCE(s->memcg_params.deact_fn))
> - return;
> + __kmemcg_cache_deactivate_after_rcu(s);
> +}
> +
> +static void kmemcg_cache_deactivate(struct kmem_cache *s)
> +{
> + __kmemcg_cache_deactivate(s);
>
> if (s->memcg_params.root_cache->memcg_params.dying)
> return;
> @@ -750,8 +742,9 @@ void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
> /* pin memcg so that @s doesn't get destroyed in the middle */
> css_get(&s->memcg_params.memcg->css);
>
> - s->memcg_params.deact_fn = deact_fn;
> - call_rcu(&s->memcg_params.deact_rcu_head, kmemcg_deactivate_rcufn);
> + WARN_ON_ONCE(s->memcg_params.work_fn);
> + s->memcg_params.work_fn = kmemcg_cache_deactivate_after_rcu;
> + call_rcu(&s->memcg_params.rcu_head, kmemcg_schedule_work_after_rcu);
> }
>
> void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
> @@ -773,7 +766,7 @@ void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
> if (!c)
> continue;
>
> - __kmemcg_cache_deactivate(c);
> + kmemcg_cache_deactivate(c);
> arr->entries[idx] = NULL;
> }
> mutex_unlock(&slab_mutex);
> @@ -866,11 +859,12 @@ static void flush_memcg_workqueue(struct kmem_cache *s)
> mutex_unlock(&slab_mutex);
>
> /*
> - * SLUB deactivates the kmem_caches through call_rcu. Make
> + * SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
> * sure all registered rcu callbacks have been invoked.
> */
> - if (IS_ENABLED(CONFIG_SLUB))
> - rcu_barrier();
> +#ifndef CONFIG_SLOB
> + rcu_barrier();
> +#endif
>
> /*
> * SLAB and SLUB create memcg kmem_caches through workqueue and SLUB
> diff --git a/mm/slub.c b/mm/slub.c
> index 16f7e4f5a141..43c34d54ad86 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4028,7 +4028,7 @@ int __kmem_cache_shrink(struct kmem_cache *s)
> }
>
> #ifdef CONFIG_MEMCG
> -static void kmemcg_cache_deact_after_rcu(struct kmem_cache *s)
> +void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
> {
> /*
> * Called with all the locks held after a sched RCU grace period.
> @@ -4054,12 +4054,6 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
> */
> slub_set_cpu_partial(s, 0);
> s->min_partial = 0;
> -
> - /*
> - * s->cpu_partial is checked locklessly (see put_cpu_partial), so
> - * we have to make sure the change is visible before shrinking.
> - */
> - slab_deactivate_memcg_cache_rcu_sched(s, kmemcg_cache_deact_after_rcu);
> }
> #endif /* CONFIG_MEMCG */
>
> --
> 2.20.1
>