On Tue, 9 Feb 2010 09:32:46 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> On Sat, 6 Feb 2010 01:30:49 +0900
> Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> > I am not sure how many usecase is also dependent of other locks.
> > If it is not as is, we can't make sure in future.
> >
> > So How about try_task_in_mem_cgroup?
> > If we can't hold task_lock, let's continue next child.
> >
> It's recommended not to use trylock in unclear case.
>
> Then, I think possible replacement will be not-to-use any lock in
> task_in_mem_cgroup. In my short consideration, I don't think task_lock
> is necessary if we can add some tricks and memory barrier.
>
> Please let this patch to go as it is because this is an obvious bug fix
> and give me time.
>
I'll try some today. please wait.
(but I wonder the patch will be not good for stable tree.)
Thanks,
-Kame
> Now, I think of following.
> This makes use of the fact mm->owner is changed only at _exit() of the owner.
> If there is a race with _exit() and mm->owner is racy, the oom selection
> itself was racy and bad.
> ==
> int task_in_mem_cgroup_oom(struct task_struct *tsk, struct mem_cgroup *mem)
> {
> struct mm_struct *mm;
> struct task_struct *tsk;
> int ret = 0;
>
> mm = tsk->mm;
> if (!mm)
> return ret;
> /*
> * we are not interested in tasks other than owner. mm->owner is
> * updated when the owner task exits. If the owner is exiting now
> * (and race with us), we may miss.
> */
> if (rcu_dereference(mm->owner) != tsk)
> return ret;
> rcu_read_lock();
> /* while this task is alive, this task is the owner */
> if (mem == mem_cgroup_from_task(tsk))
> ret = 1;
> rcu_read_unlock();
> return ret;
> }
> ==
> Hmm, it seems no memory barrier is necessary.
>
> Does anyone has another idea ?
>
> Thanks,
> -Kame
>
>
>
>
>
>
>
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