Re: oom-reaper choosing wrong processes.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Dave Jones wrote:
> On Tue, Jul 19, 2016 at 07:52:28PM +0900, Tetsuo Handa wrote:
>  > On 2016/07/19 8:18, Dave Jones wrote:
>  > > Whoa. Why did it pick systemd-journal ?
>  > 
>  > I guess that it is because all trinity processes' mm already had MMF_OOM_REAPED set.
>  > 
>  > The OOM reaper sets MMF_OOM_REAPED when OOM reap operation succeeded. But
>  > "[ pid ]   uid  tgid total_vm      rss nr_ptes nr_pmds swapents oom_score_adj name" listing
>  > includes processes whose mm already has MMF_OOM_REAPED set. As a result, trinity-c15 and
>  > trinity-c4 are shown again in the listing. While I can't confirm that trinity-c10, trinity-c2,
>  > trinity-c0 and trinity-c11 are already OOM killed, I guess they are already OOM killed and
>  > their mm already had MMF_OOM_REAPED set.
> 
> That still doesn't explain why it picked the journal process, instead of waiting until
> the previous reaping operation had actually killed those Trinity tasks.

I thought your patch did

--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -169,6 +169,8 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
 
 	if (oom_unkillable_task(p, memcg, nodemask))
 		return 0;
+	if (!strncmp(p->comm, "trinity-", 8))
+		return 0;
 
 	p = find_lock_task_mm(p);
 	if (!p)

to OOM-kill only Trinity tasks. But your patch did not touch OOM victim selection logic.
Then, it is completely normal and expected result that systemd-journald was selected
because systemd-journald got highest score among all OOM-killable !MMF_OOM_REAPED mm
users. Nothing is wrong.

By the way, your patch needs to call put_task_struct(p) before return.

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