From: Tejun Heo <tj@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov@virtuozzo.com>,
Michal Hocko <mhocko@suse.cz>, Li Zefan <lizefan@huawei.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] mm: memcontrol: fix cgroup creation failure after many small jobs
Date: Thu, 16 Jun 2016 16:06:17 -0400 [thread overview]
Message-ID: <20160616200617.GD3262@mtj.duckdns.org> (raw)
In-Reply-To: <20160616034244.14839-1-hannes@cmpxchg.org>
Hello,
Looks generally good to me. Some comments below.
On Wed, Jun 15, 2016 at 11:42:44PM -0400, Johannes Weiner wrote:
> @@ -6205,6 +6205,24 @@ struct cgroup *cgroup_get_from_path(const char *path)
> }
> EXPORT_SYMBOL_GPL(cgroup_get_from_path);
>
> +/**
> + * css_id_free - relinquish an existing CSS's ID
> + * @css: the CSS
> + *
> + * This releases the @css's ID and allows it to be recycled while the
> + * CSS continues to exist. This is useful for controllers with state
> + * that extends past a cgroup's lifetime but doesn't need precious ID
> + * address space.
> + *
> + * This invalidates @css->id, and css_from_id() might return NULL or a
> + * new css if the ID has been recycled in the meantime.
> + */
> +void css_id_free(struct cgroup_subsys_state *css)
> +{
> + cgroup_idr_remove(&css->ss->css_idr, css->id);
> + css->id = 0;
> +}
I don't quite get why we're trying to free css->id earlier when memcg
is gonna be using its private id anyway. From cgroup core side, the
id space isn't restricted.
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 75e74408cc8f..1d8a6dffdc25 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
...
> +static void mem_cgroup_id_put(struct mem_cgroup *memcg)
> +{
> + if (atomic_dec_and_test(&memcg->id.ref)) {
> + idr_remove(&mem_cgroup_idr, memcg->id.id);
Maybe this should do "memcg->id.id = 0"?
> + css_id_free(&memcg->css);
> + css_put(&memcg->css);
> + }
> +}
> +
> +/**
> + * mem_cgroup_from_id - look up a memcg from a memcg id
> + * @id: the memcg id to look up
> + *
> + * Caller must hold rcu_read_lock().
> + */
> +struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
> +{
> + WARN_ON_ONCE(!rcu_read_lock_held());
> + return id > 0 ? idr_find(&mem_cgroup_idr, id) : NULL;
> +}
css_from_id() has it too but I don't think id > 0 test is necessary.
We prolly should take it out of css_from_id() too.
It might be useful to add comment explaining why memcg needs private
ids.
Thanks.
--
tejun
next prev parent reply other threads:[~2016-06-16 20:06 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-16 3:42 [PATCH] mm: memcontrol: fix cgroup creation failure after many small jobs Johannes Weiner
2016-06-16 20:06 ` Tejun Heo [this message]
2016-06-17 16:23 ` Johannes Weiner
2016-06-17 16:23 ` [PATCH 1/3] cgroup: fix idr leak for the first cgroup root Johannes Weiner
2016-06-17 16:24 ` [PATCH 2/3] cgroup: remove unnecessary 0 check from css_from_id() Johannes Weiner
2016-06-17 18:17 ` Tejun Heo
2016-06-17 16:25 ` [PATCH 3/3] mm: memcontrol: fix cgroup creation failure after many small jobs Johannes Weiner
2016-06-17 18:18 ` Tejun Heo
2016-06-20 6:14 ` Nikolay Borisov
2016-06-21 10:16 ` Vladimir Davydov
2016-06-21 15:46 ` Johannes Weiner
2016-06-17 9:06 ` [PATCH] " Vladimir Davydov
2016-06-17 16:40 ` Johannes Weiner
2016-07-14 15:37 ` Johannes Weiner
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