From: Oleg Nesterov <oleg@redhat.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
Tejun Heo <tj@kernel.org>,
Vladimir Davydov <vdavydov@parallels.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 3/3] memcg: get rid of mm_struct::owner
Date: Tue, 26 May 2015 19:38:22 +0200 [thread overview]
Message-ID: <20150526173822.GA31777@redhat.com> (raw)
In-Reply-To: <20150526172234.GK14681@dhcp22.suse.cz>
On 05/26, Michal Hocko wrote:
>
> On Tue 26-05-15 18:36:46, Oleg Nesterov wrote:
> >
> > > +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.
>
> This hasn't changed by this patch. mem_cgroup_from_task was allowed to
> return NULL even before. I've just made it static because it doesn't
> have any external users anymore.
I see, but it could only return NULL if mem_cgroup_from_css() returns
NULL. Now it returns NULL for sure if the caller is task_in_mem_cgroup(),
// called when task->mm == NULL
task_memcg = mem_cgroup_from_task(task);
css_get(&task_memcg->css);
and this css_get() doesn't look nice if task_memcg == NULL ;)
> I will double check
Yes, please. Perhaps I missed something.
> > And in fact I can't understand what mem_cgroup_from_task() actually
> > means, with or without these changes.
>
> It performs task_struct->mem_cgroup mapping. We cannot use cgroup
> mapping here because the charges are bound to mm_struct rather than
> task.
Sure, this is what I can understand. I meant... OK, lets ignore
"without these changes", because without these changes there are
much more oddities ;) With these changes only ->mm == NULL case
looks unclear.
And btw,
if (!p->mm)
return NULL;
return rcu_dereference(p->mm->memcg);
perhaps this needs a comment. It is not clear what protects ->mm.
But. After this series "p" is always current (if ->mm != NULL), so
this is fine.
Nevermind. Please forget. I feel this needs a bit of cleanup, but
we can always do this later.
Oleg.
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next prev parent reply other threads:[~2015-05-26 17:39 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-26 11:50 [RFC 0/3] get rid of mm_struct::owner Michal Hocko
2015-05-26 11:50 ` [RFC 1/3] memcg: restructure mem_cgroup_can_attach() Michal Hocko
2015-05-26 11:50 ` [RFC 2/3] memcg: Use mc.moving_task as the indication for charge moving Michal Hocko
2015-05-26 11:50 ` [RFC 3/3] memcg: get rid of mm_struct::owner Michal Hocko
2015-05-26 14:10 ` Johannes Weiner
2015-05-26 15:11 ` Michal Hocko
2015-05-26 17:20 ` Johannes Weiner
2015-05-27 14:48 ` Michal Hocko
2015-05-28 21:07 ` Tejun Heo
2015-05-29 12:08 ` Michal Hocko
2015-05-29 13:10 ` Tejun Heo
2015-05-29 13:45 ` Michal Hocko
2015-05-29 14:07 ` Tejun Heo
2015-05-29 14:57 ` Michal Hocko
2015-05-29 15:23 ` Tejun Heo
2015-05-29 15:26 ` Michal Hocko
2015-05-26 16:36 ` Oleg Nesterov
2015-05-26 17:22 ` Michal Hocko
2015-05-26 17:38 ` Oleg Nesterov [this message]
2015-05-27 9:43 ` Michal Hocko
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