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SubjectRe: [patch -mm v2] mm: introduce oom_adj_child

Sorry for queue jumping. I have one question.

> > > - /proc/pid/oom_score is inconsistent when the thread that set the
> > > effective per-mm oom_adj exits and it is now obsolete since you have
> > > no way to determine what the next effective oom_adj value shall be.
> > >
> > plz re-caluculate it. it's not a big job if done in lazy way.
> >
> You can't recalculate it if all the remaining threads have a different
> oom_adj value than the effective oom_adj value from the thread that is now
> exited. There is no assumption that, for instance, the most negative
> oom_adj value shall then be used. Imagine the effective oom_adj value
> being +15 and a thread sharing the same memory has an oom_adj value of
> -16. Under no reasonable circumstance should the oom preference of the
> entire thread then change to -16 just because its the side-effect of a
> thread exiting.

Why do we need recaluculate AT thread exiting time?
it is only used when oom_score is readed or actual OOM happend.
both those are slow-path.

> That's the _entire_ reason why we need consistency in oom_adj values so
> that userspace is aware of how the oom killer really works and chooses
> tasks. I understand that it differs from the previously allowed behavior,
> but those userspace applications need to be fixed if, for no other reason,
> they are now consistent with how the oom killer kills tasks. I think
> that's a very worthwhile goal and the cost of moving to a new interface
> such as /proc/pid/oom_adj_child to have the same inheritance property that
> was available in the past is justified.

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