Oleg Nesterov wrote:
> Since I mentioned TIF_MEMDIE in another thread, I simply can't resist.
> Sorry for grunting.
>
> On 06/24, Tetsuo Handa wrote:
> >
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -801,6 +801,7 @@ struct signal_struct {
> > * oom
> > */
> > bool oom_flag_origin;
> > + bool oom_ignore_victims; /* Ignore oom_victims value */
> > short oom_score_adj; /* OOM kill score adjustment */
> > short oom_score_adj_min; /* OOM kill score adjustment min value.
> > * Only settable by CAP_SYS_RESOURCE. */
>
> Yet another kludge to fix yet another problem with TIF_MEMDIE. Not
> to mention that that wh
>
> Can't we state the fact TIF_MEMDIE is just broken? The very idea imo.
Yes. TIF_MEMDIE is a trouble maker.
Setting TIF_MEMDIE is per task_struct operation.
Sending SIGKILL is per signal_struct operation.
OOM killer is per mm_struct operation.
> I am starting to seriously think we should kill this flag, fix the
> compilation errors, remove the dead code (including the oom_victims
> logic), and then try to add something else. Say, even MMF_MEMDIE looks
> better although I understand it is not that simple.
I wish that TIF_MEMDIE is per signal_struct flag. But since we allow
mm-less TIF_MEMDIE thread to use ALLOC_NO_WATERMARKS via TIF_MEMDIE
inside __mmput() from mmput() from exit_mm() from do_exit(), we can't
replace
test_thread_flag(TIF_MEMDIE)
in gfp_to_alloc_flags() with
current->signal->oom_killed
or
current->mm && (current->mm->flags & MMF_MEMDIE)
. But
>
> Just one question. Why do we need this bit outside of oom-kill.c? It
> affects page_alloc.c and this probably makes sense. But who get this
> flag when we decide to kill the memory hog? A random thread foung by
> find_lock_task_mm(), iow a random thread with ->mm != NULL, likely the
> group leader. This simply can not be right no matter what.
I agree that setting TIF_MEMDIE to only first ->mm != NULL thread
does not make sense.
I've proposed setting TIF_MEMDIE to all ->mm != NULL threads which are
killed by the OOM killer because doing so won't increase the risk of
depleting the memory reserves, for TIF_MEMDIE helps only if that thread is
doing memory allocation
( http://lkml.kernel.org/r/1458529634-5951-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx ),
but it did not happen.
>
> And in any case I don't understand this patch but I have to admit that
> I failed to force myself to read the changelog and the actual change ;)
> In any case I agree that we should not set MMF_MEMDIE if ->mm == NULL,
> and if we ensure this then I do not understand why we can't rely on
> MMF_OOM_REAPED. Ignoring the obvious races, if ->oom_victims != 0 then
> find_lock_task_mm() should succed.
Since we are using
mm = current->mm;
current->mm = NULL;
__mmput(mm); (may block for unbounded period waiting for somebody else's memory allocation)
exit_oom_victim(current);
sequence, we won't be able to make find_lock_task_mm(tsk) != NULL when
tsk->signal->oom_victims != 0 unless we change this sequence.
My patch tries to rescue it using tsk->signal->oom_ignore_victims flag.
>
> Oleg.
>
>
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