Messages in this thread | | | Date | Wed, 02 Apr 2008 08:55:34 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][-mm] Add an owner to the mm_struct (v4) |
| |
KAMEZAWA Hiroyuki wrote: > On Tue, 01 Apr 2008 18:13:12 +0530 > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: >> + /* >> + * Search in the children >> + */ >> + list_for_each_entry(c, &p->children, sibling) { >> + if (c->mm == mm) >> + goto assign_new_owner; >> + } >> + > This finds new owner when "current" is multi-threaded and > "current" called pthread_create(), right ? >
No, it won't find the new owner if we have CLONE_THREAD passed while creating threads. mm_need_new_owner() checks for !delay_group_leader(). If the group_leader is set, we don't need a new owner, it stays around till all threads exit.
>> + /* >> + * Search in the siblings >> + */ >> + list_for_each_entry(c, &p->parent->children, sibling) { >> + if (c->mm == mm) >> + goto assign_new_owner; >> + } >> + > This finds new owner when "current" is multi-threaded and > "current" is just a child (means it doesn't call pthread_create()) ? >
Ditto
> >> + /* >> + * Search through everything else. We should not get >> + * here often >> + */ >> + do_each_thread(g, c) { >> + if (c->mm == mm) >> + goto assign_new_owner; >> + } while_each_thread(g, c); > > Doing above in synchronized manner seems too heavy. > When this happen ? or Can this be done in lazy "on-demand" manner ? >
Do you mean under task_lock()?
> +assign_new_owner: > + rcu_read_unlock(); > + BUG_ON(c == p); > + task_lock(c); > + if (c->mm != mm) { > + task_unlock(c); > + goto retry; > + } > + cgroup_mm_owner_callbacks(mm->owner, c); > + mm->owner = c; > + task_unlock(c); > +} > Why rcu_read_unlock() before changing owner ? Is it safe ? >
It should be safe, since we take task_lock(), but to be doubly sure, we can drop rcu read lock after taking the task_lock().
-- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL
| |