Messages in this thread |  | | Date | Tue, 27 Aug 2013 18:15:36 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 11/12] pid: rewrite task helper functions avoiding task->pid and task->tgid |
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On 08/26, Richard Guy Briggs wrote: > > On Thu, Aug 22, 2013 at 09:08:48PM +0200, Oleg Nesterov wrote: > > On 08/20, Richard Guy Briggs wrote: > > > > > > static inline int is_global_init(struct task_struct *tsk) > > > { > > > - return tsk->pid == 1; > > > + return task_pid_nr(tsk) == 1; > > > } > > > > Probably it would be better to simply kill it. Almost every usage is > > wrong. > > Can you be more clear? I don't follow. It should instead return a > boolean. Usage of is_global_init() or task_pid_nr()?
Just look at the callers. For example, how is_global_init() can save /sbin/init from oom-killer if it is multithreaded ?
> If is_global_init(), is that because they could be unaware of pid > namespaces?
Because I think nobody actually needs is_a_group_leader_of_global_init(), and this is what this helper actually is.
> > > static inline bool is_idle_task(const struct task_struct *p) > > > { > > > - return p->pid == 0; > > > + return task_pid(p) == &init_struct_pid; > > > } > > > > hmm. there should be a simpler check for this... > > Other than the original, this one is pretty simple.
I meant that the original check is cheaper,
> What did you have > in mind?
Well. I agree that it would be nice to avoid the dependence on task->pid if possible. And perhaps even kill it eventually. But I am not sure how much we should try.
If it was the last user of ->pid, then I would agree with this change. Although we can make it cheaper, say, we can change idle_init() to nullify tasks->next and use ->next == NULL.
But we have a lot more ->pid users, perhaps we should change them first.
And more importantly, let me repeat. I do not think that this change should be mixed with other changes in this series.
> > > static inline int has_group_leader_pid(struct task_struct *p) > > > { > > > - return p->pid == p->tgid; > > > + return task_pid(p) == task_tgid(p); > > > } > > > > > > static inline > > > int same_thread_group(struct task_struct *p1, struct task_struct *p2) > > > { > > > - return p1->tgid == p2->tgid; > > > + return task_tgid(p1) == task_tgid(p2); > > > > This is suboptinal. See the attached > > include-linux-schedh-dont-use-task-pid-tgid-in-same_thread_group-has_group_leader_pid.patch > > from -mm below. > > I'm fine with that if it is deemed better. The point was to remove the > dependence on task_struct::tgid.
But I agree! My only point was, this conflicts with the patch we already have and that patch is more optimal. p1->leader == p2->leader is cheaper.
Oleg.
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