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SubjectRe: [PATCH -mm 2/3] mm/oom_kill: cleanup the "kill sharing same memory"
On Tue, 29 Sep 2015, Oleg Nesterov wrote:

> Purely cosmetic, but the complex "if" condition looks annoying to me.
> Especially because it is not consistent with OOM_SCORE_ADJ_MIN check
> which adds another if/continue.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> mm/oom_kill.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 0d581c6..8e7bed2 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -583,16 +583,20 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
> * pending fatal signal.
> */
> rcu_read_lock();
> - for_each_process(p)
> - if (p->mm == mm && !same_thread_group(p, victim) &&
> - !(p->flags & PF_KTHREAD)) {
> - if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> - continue;
> + for_each_process(p) {
> + if (unlikely(p->flags & PF_KTHREAD))
> + continue;
> + if (same_thread_group(p, victim))
> + continue;
> + if (p->mm != mm)
> + continue;

This ordering is a little weird to me, I think we would eliminate the
majority of processes by checking for p->mm != mm first. There are
certainly pathological cases where that can be defeated, but in practice
it seems to happen more often than not.

Unless you object, I think the ordering should be p->mm != mm,
same_thread_group(), unlikely(PF_KTHREAD) as it originally was (thanks for
adding the unlikely).

I agree your cleanup looks much better than the nested conditional.


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