On Tue 12-01-16 20:32:18, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > On Fri 08-01-16 00:38:43, Tetsuo Handa wrote:
> > > Michal Hocko wrote:
> > > > @@ -333,6 +333,14 @@ static struct task_struct *select_bad_process(struct oom_control *oc,
> > > > if (points == chosen_points && thread_group_leader(chosen))
> > > > continue;
> > > >
> > > > + /*
> > > > + * If the current major task is already ooom killed and this
> > > > + * is sysrq+f request then we rather choose somebody else
> > > > + * because the current oom victim might be stuck.
> > > > + */
> > > > + if (is_sysrq_oom(sc) && test_tsk_thread_flag(p, TIF_MEMDIE))
> > > > + continue;
> > > > +
> > > > chosen = p;
> > > > chosen_points = points;
> > > > }
> > >
> > > Do we want to require SysRq-f for each thread in a process?
> > > If g has 1024 p, dump_tasks() will do
> > >
> > > pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu %5hd %s\n",
> > >
> > > for 1024 times? I think one SysRq-f per one process is sufficient.
> >
> > I am not following you here. If we kill the process the whole process
> > group (aka all threads) will get killed which ever thread we happen to
> > send the sigkill to.
>
> Please distinguish "sending SIGKILL to a process" and "all threads in that
> process terminate".
I didn't say anything about termination if your read my response again.
[...]
> > > How can we guarantee that find_lock_task_mm() from oom_kill_process()
> > > chooses !TIF_MEMDIE thread when try_to_sacrifice_child() somehow chose
> > > !TIF_MEMDIE thread? I think choosing !TIF_MEMDIE thread at
> > > find_lock_task_mm() is the simplest way.
> >
> > find_lock_task_mm chosing TIF_MEMDIE thread shouldn't change anything
> > because the whole thread group will go down anyway. If you want to
> > guarantee that the sysrq+f never choses a task which has a TIF_MEMDIE
> > thread then we would have to check for fatal_signal_pending as well
> > AFAIU. Fiddling with find find_lock_task_mm will not help you though
> > unless I am missing something.
>
> I do want to guarantee that the SysRq-f (and timeout based next victim
> selection) never chooses a process which has a TIF_MEMDIE thread.
Sigh... see what I have written in the paragraph you are replying to...
> I don't like current "oom: clear TIF_MEMDIE after oom_reaper managed to unmap
> the address space" patch unless both "mm,oom: exclude TIF_MEMDIE processes from
> candidates." patch and "mm,oom: Re-enable OOM killer using timers."
Those patches are definitely not a prerequisite from the functional
point of view and putting them together as a prerequisite sounds like
blocking a useful feature without technical grounds to me.
--
Michal Hocko
SUSE Labs
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