From: Michal Hocko <mhocko@kernel.org>
To: David Rientjes <rientjes@google.com>
Cc: linux-mm@kvack.org,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 2/3] oom: Do not sacrifice already OOM killed children
Date: Wed, 13 Jan 2016 10:36:02 +0100 [thread overview]
Message-ID: <20160113093601.GB28942@dhcp22.suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.10.1601121644250.28831@chino.kir.corp.google.com>
On Tue 12-01-16 16:45:35, David Rientjes wrote:
> On Tue, 12 Jan 2016, Michal Hocko wrote:
>
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 2b9dc5129a89..8bca0b1e97f7 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -671,6 +671,63 @@ static bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
> > }
> >
> > #define K(x) ((x) << (PAGE_SHIFT-10))
> > +
> > +/*
> > + * If any of victim's children has a different mm and is eligible for kill,
> > + * the one with the highest oom_badness() score is sacrificed for its
> > + * parent. This attempts to lose the minimal amount of work done while
> > + * still freeing memory.
> > + */
> > +static struct task_struct *
> > +try_to_sacrifice_child(struct oom_control *oc, struct task_struct *victim,
> > + unsigned long totalpages, struct mem_cgroup *memcg)
> > +{
> > + struct task_struct *child_victim = NULL;
> > + unsigned int victim_points = 0;
> > + struct task_struct *t;
> > +
> > + read_lock(&tasklist_lock);
> > + for_each_thread(victim, t) {
> > + struct task_struct *child;
> > +
> > + list_for_each_entry(child, &t->children, sibling) {
> > + unsigned int child_points;
> > +
> > + /*
> > + * Skip over already OOM killed children as this hasn't
> > + * helped to resolve the situation obviously.
> > + */
> > + if (test_tsk_thread_flag(child, TIF_MEMDIE) ||
> > + fatal_signal_pending(child) ||
> > + task_will_free_mem(child))
> > + continue;
> > +
>
> What guarantees that child had time to exit after it has been oom killed
> (better yet, what guarantees that it has even scheduled after it has been
> oom killed)? It seems like this would quickly kill many children
> unnecessarily.
If the child hasn't released any memory after all the allocator attempts to
free a memory, which takes quite some time, then what is the advantage of
waiting even more and possibly get stuck? This is a heuristic, we should
have killed the selected victim but we have chosen to reduce the impact by
selecting the child process instead. If that hasn't led to any
improvement I believe we should move on rather than looping on
potentially unresolvable situation _just because_ of the said heuristic.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-01-13 9:36 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-12 21:00 [RFC 0/3] oom: few enahancements Michal Hocko
2016-01-12 21:00 ` [RFC 1/3] oom, sysrq: Skip over oom victims and killed tasks Michal Hocko
2016-01-13 0:41 ` David Rientjes
2016-01-13 9:30 ` Michal Hocko
2016-01-14 0:38 ` David Rientjes
2016-01-14 11:00 ` Michal Hocko
2016-01-14 21:51 ` David Rientjes
2016-01-15 10:12 ` Michal Hocko
2016-01-15 15:37 ` One Thousand Gnomes
2016-01-19 23:01 ` David Rientjes
2016-01-19 22:57 ` David Rientjes
2016-01-20 9:49 ` Michal Hocko
2016-01-21 0:01 ` David Rientjes
2016-01-21 9:15 ` Michal Hocko
2016-01-12 21:00 ` [RFC 2/3] oom: Do not sacrifice already OOM killed children Michal Hocko
2016-01-13 0:45 ` David Rientjes
2016-01-13 9:36 ` Michal Hocko [this message]
2016-01-14 0:42 ` David Rientjes
2016-01-12 21:00 ` [RFC 3/3] oom: Do not try to sacrifice small children Michal Hocko
2016-01-13 0:51 ` David Rientjes
2016-01-13 9:40 ` Michal Hocko
2016-01-14 0:43 ` David Rientjes
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