linux-kernel - Re: [RFC][-mm] Add an owner to the mm

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Message-ID: <6599ad830803312316m17f9e6f1mf7f068c0314a789e@mail.gmail.com>
Date:	Mon, 31 Mar 2008 23:16:19 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>
Cc:	"Pavel Emelianov" <xemul@...nvz.org>,
	"Hugh Dickins" <hugh@...itas.com>,
	"Sudhir Kumar" <skumar@...ux.vnet.ibm.com>,
	"YAMAMOTO Takashi" <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, "David Rientjes" <rientjes@...gle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][-mm] Add an owner to the mm_struct (v3)

On Mon, Mar 31, 2008 at 10:43 PM, Balbir Singh
<balbir@...ux.vnet.ibm.com> wrote:
>  -static struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
>  +struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
>   {
>         return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
>                                 struct mem_cgroup, css);
>   }

This should probably be inlined in the header file if it's needed
outside this file.
>  +static inline void mm_fork_init_owner(struct task_struct *p)
>  +{
>  +}

I think this is stale.

>  +
>  +void mm_update_next_owner(struct mm_struct *mm)
>  +{
>  +       struct task_struct *c, *g, *p = current;
>  +
>  +       /*
>  +        * This routine should not be called for init_task
>  +        */
>  +       BUG_ON(p == p->parent);

I think (as you mentioned earlier) that we need an RCU critical
section in this function, in order for the tasklist traversal to be
safe.

Maybe also BUG_ON(p != mm->owner) ?

>  +       list_for_each_entry(c, &p->children, sibling) {
>  +               if (c->mm && (c->mm == mm))

Since mm != NULL, no need to test for c->mm since if it's NULL then c->mm != mm

>  +assign_new_owner:
>  +       BUG_ON(c == p);
>  +       task_lock(c);
>  +       if (c->mm != mm) {
>  +               task_unlock(c);
>  +               goto retry;
>  +       }
>  +       mm->owner = c;

Here we'll want to call vm_cgroup_update_mm_owner(), to adjust the
accounting. (Or if in future we end up with more than a couple of
subsystems that want notification at this time, we'll want to call
cgroup_update_mm_owner() and have it call any interested subsystems.

Paul
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