Home » Mailing lists » Devel » [PATCH v5 00/18] slab accounting for memcg
| Re: [PATCH v5 08/18] memcg: infrastructure to match an allocation to the right cache [message #48605 is a reply to message #48533] |
Wed, 24 October 2012 18:10   |
JoonSoo Kim
Messages: 9
Registered: September 2012
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Junior Member |
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2012/10/19 Glauber Costa <glommer@parallels.com>:
> @@ -2930,9 +2937,188 @@ int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s)
>
> void memcg_release_cache(struct kmem_cache *s)
> {
> + struct kmem_cache *root;
> + int id = memcg_css_id(s->memcg_params->memcg);
> +
> + if (s->memcg_params->is_root_cache)
> + goto out;
> +
> + root = s->memcg_params->root_cache;
> + root->memcg_params->memcg_caches[id] = NULL;
> + mem_cgroup_put(s->memcg_params->memcg);
> +out:
> kfree(s->memcg_params);
> }
memcg_css_id should be called after checking "s->memcg_params->is_root_cache".
Because when is_root_cache == true, memcg_params has no memcg object.
> +/*
> + * This lock protects updaters, not readers. We want readers to be as fast as
> + * they can, and they will either see NULL or a valid cache value. Our model
> + * allow them to see NULL, in which case the root memcg will be selected.
> + *
> + * We need this lock because multiple allocations to the same cache from a non
> + * GFP_WAIT area will span more than one worker. Only one of them can create
> + * the cache.
> + */
> +static DEFINE_MUTEX(memcg_cache_mutex);
> +static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> + struct kmem_cache *cachep)
> +{
> + struct kmem_cache *new_cachep;
> + int idx;
> +
> + BUG_ON(!memcg_can_account_kmem(memcg));
> +
> + idx = memcg_css_id(memcg);
> +
> + mutex_lock(&memcg_cache_mutex);
> + new_cachep = cachep->memcg_params->memcg_caches[idx];
> + if (new_cachep)
> + goto out;
> +
> + new_cachep = kmem_cache_dup(memcg, cachep);
> +
> + if (new_cachep == NULL) {
> + new_cachep = cachep;
> + goto out;
> + }
> +
> + mem_cgroup_get(memcg);
> + cachep->memcg_params->memcg_caches[idx] = new_cachep;
> + wmb(); /* the readers won't lock, make sure everybody sees it */
Is there any rmb() pair?
As far as I know, without rmb(), wmb() doesn't guarantee anything.
> + new_cachep->memcg_params->memcg = memcg;
> + new_cachep->memcg_params->root_cache = cachep;
It may be better these assignment before the statement
"cachep->memcg_params->memcg_caches[idx] = new_cachep".
Otherwise, it may produce race situation.
And assigning value to memcg_params->memcg and root_cache is redundant,
because it is already done in memcg_register_cache().
> +/*
> + * Return the kmem_cache we're supposed to use for a slab allocation.
> + * We try to use the current memcg's version of the cache.
> + *
> + * If the cache does not exist yet, if we are the first user of it,
> + * we either create it immediately, if possible, or create it asynchronously
> + * in a workqueue.
> + * In the latter case, we will let the current allocation go through with
> + * the original cache.
> + *
> + * Can't be called in interrupt context or from kernel threads.
> + * This function needs to be called with rcu_read_lock() held.
> + */
> +struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
> + gfp_t gfp)
> +{
> + struct mem_cgroup *memcg;
> + int idx;
> +
> + if (cachep->memcg_params && cachep->memcg_params->memcg)
> + return cachep;
In __memcg_kmem_get_cache, cachep may be always root cache.
So checking "cachep->memcg_params->memcg" is somewhat strange.
Is it right?
Thanks.
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