Re: [RFC 1/3] oom, sysrq: Skip over oom victims and killed tasks
From: David Rientjes
Date: Tue Jan 12 2016 - 19:41:55 EST
On Tue, 12 Jan 2016, Michal Hocko wrote:
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index abefeeb42504..2b9dc5129a89 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -326,6 +326,17 @@ static struct task_struct *select_bad_process(struct oom_control *oc,
> case OOM_SCAN_OK:
> break;
> };
> +
> + /*
> + * If we are doing sysrq+f then it doesn't make any sense to
> + * check OOM victim or killed task because it might be stuck
> + * and unable to terminate while the forced OOM might be the
> + * only option left to get the system back to work.
> + */
> + if (is_sysrq_oom(oc) && (test_tsk_thread_flag(p, TIF_MEMDIE) ||
> + fatal_signal_pending(p)))
> + continue;
> +
> points = oom_badness(p, NULL, oc->nodemask, totalpages);
> if (!points || points < chosen_points)
> continue;
I think you can make a case for testing TIF_MEMDIE here since there is no
chance of a panic from the sysrq trigger. However, I'm not convinced that
checking fatal_signal_pending() is appropriate. I think it would be
better for sysrq+f to first select a process with fatal_signal_pending()
set so it silently gets access to memory reserves and then a second
sysrq+f to choose a different process, if necessary, because of
TIF_MEMDIE.