Re: [PATCH 11/12] pid: rewrite task helper functions avoiding task->pid and task->tgid
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.