Messages in this thread | | | Date | Thu, 30 Jul 2009 00:06:38 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [patch -mm v2] mm: introduce oom_adj_child |
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On Thu, 30 Jul 2009, KOSAKI Motohiro wrote:
> > diff --git a/kernel/fork.c b/kernel/fork.c > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -426,7 +426,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p) > > init_rwsem(&mm->mmap_sem); > > INIT_LIST_HEAD(&mm->mmlist); > > mm->flags = (current->mm) ? current->mm->flags : default_dump_filter; > > - mm->oom_adj = (current->mm) ? current->mm->oom_adj : 0; > > + mm->oom_adj = p->oom_adj_child; > > This code doesn't fix anything. > mm->oom_adj assignment still change vfork() parent process oom_adj value. > (Again, vfork() parent and child use the same mm) >
That's because the oom killer only really considers the highest oom_adj value amongst all threads that share the same mm. Allowing those threads to each have different oom_adj values leads (i) to an inconsistency in reporting /proc/pid/oom_score for how the oom killer selects a task to kill and (ii) the oom killer livelock that it fixes when one thread happens to be OOM_DISABLE.
So, yes, changing the oom_adj value for a thread may have side-effects on other threads that didn't exist prior to 2.6.31-rc1 because the oom_adj value now represents a killable quantity of memory instead of a being a characteristic of the task itself. But we now provide the inheritance property in a new way, via /proc/pid/oom_adj_child, that gives you all the functionality that the previous way did but without the potential for livelock.
> IOW, in vfork case, oom_adj_child parameter doesn't only change child oom_adj, > but also parent oom_adj value.
Changing oom_adj_child for a task never changes oom_adj for any mm, it simply specifies what default value shall be given for a child's newly initialized mm. Chaning oom_adj, on the other hand, will
> IOW, oom_adj_child is NOT child effective parameter. >
It's not meant to be, it's only meant to specify a default value for newly initialized mm's of its descendants. What happens after that is governed completely by the child's own /proc/pid/oom_adj. That's pretty clearly explained in Documentation/filesystems/proc.txt.
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