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Message-ID: <20150526163646.GA29968@redhat.com>
Date: Tue, 26 May 2015 18:36:46 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Michal Hocko <mhocko@...e.cz>
Cc: linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
Tejun Heo <tj@...nel.org>,
Vladimir Davydov <vdavydov@...allels.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 3/3] memcg: get rid of mm_struct::owner
On 05/26, Michal Hocko wrote:
>
> @@ -426,17 +426,7 @@ struct mm_struct {
> struct kioctx_table __rcu *ioctx_table;
> #endif
> #ifdef CONFIG_MEMCG
> - /*
> - * "owner" points to a task that is regarded as the canonical
> - * user/owner of this mm. All of the following must be true in
> - * order for it to be changed:
> - *
> - * current == mm->owner
> - * current->mm != mm
> - * new_owner->mm == mm
> - * new_owner->alloc_lock is held
> - */
> - struct task_struct __rcu *owner;
> + struct mem_cgroup __rcu *memcg;
Yes, thanks, this is what I tried to suggest ;)
But I can't review this series. Simply because I know nothing about
memcs. I don't even know how to use it.
Just one question,
> +static struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
> +{
> + if (!p->mm)
> + return NULL;
> + return rcu_dereference(p->mm->memcg);
> +}
Probably I missed something, but it seems that the callers do not
expect it can return NULL. Perhaps sock_update_memcg() is fine, but
task_in_mem_cgroup() calls it when find_lock_task_mm() fails, and in
this case ->mm is NULL.
And in fact I can't understand what mem_cgroup_from_task() actually
means, with or without these changes.
And another question. I can't understand what happens when a task
execs... IOW, could you confirm that exec_mmap() does not need
mm_set_memcg(mm, oldmm->memcg) ?
Oleg.
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