From: Michal Hocko <mhocko@kernel.org>
To: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: linux-mm@kvack.org,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
David Rientjes <rientjes@google.com>,
Oleg Nesterov <oleg@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj
Date: Mon, 30 May 2016 14:28:14 +0200 [thread overview]
Message-ID: <20160530122814.GX22928@dhcp22.suse.cz> (raw)
In-Reply-To: <20160530121932.GC8293@esperanza>
On Mon 30-05-16 15:19:32, Vladimir Davydov wrote:
> On Mon, May 30, 2016 at 01:11:48PM +0200, Michal Hocko wrote:
> > On Mon 30-05-16 13:26:44, Vladimir Davydov wrote:
> > > On Mon, May 30, 2016 at 11:39:50AM +0200, Michal Hocko wrote:
> > [...]
> > > > Yes and that leads me to a suspicion that we can do that. Maybe I should
> > > > just add a note into the log that we are doing that so that people can
> > > > complain? Something like the following
> > > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > > index fa0b3ca94dfb..7f3495415719 100644
> > > > --- a/fs/proc/base.c
> > > > +++ b/fs/proc/base.c
> > > > @@ -1104,7 +1104,6 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > > > err_sighand:
> > > > unlock_task_sighand(task, &flags);
> > > > err_put_task:
> > > > - put_task_struct(task);
> > > >
> > > > if (mm) {
> > > > struct task_struct *p;
> > > > @@ -1113,6 +1112,10 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > > > for_each_process(p) {
> > > > task_lock(p);
> > > > if (!p->vfork_done && process_shares_mm(p, mm)) {
> > > > + pr_info("updating oom_score_adj for %d (%s) from %d to %d because it shares mm with %d (%s). Report if this is unexpected.\n",
> > > > + task_pid_nr(p), p->comm,
> > > > + p->signal->oom_score_adj, oom_adj,
> > > > + task_pid_nr(task), task->comm);
> > >
> > > IMO this could be acceptable from userspace pov, but I don't very much
> > > like how vfork is special-cased here and in oom killer code.
> >
> > Well, the vfork has to be special cased here. We definitely have to
> > support
> > vfork()
> > set_oom_score_adj()
> > exec()
> >
> > use case. And I do not see other way without adding something to the
> > clone hot paths which sounds like not justifiable considering we are
> > talking about a really rare usecase that basically nobody cares about.
>
> I don't think that vfork->exec use case is rare. Quite the contrary, I'm
> pretty sure it's used often, because in contrast to fork->exec it avoids
> copying page tables, which can be very expensive for fat processes.
Ohh, yes, the way I put it is ambiguous. What I wanted to say is that
the oom is really unlikely so it doesn't justify hot path changes.
> Frankly, I don't understand why you are so determined not to add
> anything to the fork path.
It is not just the fork path. It would require touching exit path as
well and all that code is quite complex already. I would prefer if the
oom related complexity stay in the oom proper.
> Of course, if the overhead were that
> dramatic, we would have to forget the idea, but if it were say <= 0.1 %
> for a contrived test that calls fork in a loop, IMHO the modification
> would be justified.
But why if the proc handler resp. oom_kill_process paths can handle most
cases and the occasional races should be tolerate able AFAICS.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2016-05-30 12:28 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-26 12:40 [PATCH 0/5] Handle oom bypass more gracefully Michal Hocko
2016-05-26 12:40 ` [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm Michal Hocko
2016-05-26 14:30 ` Tetsuo Handa
2016-05-26 14:59 ` Michal Hocko
2016-05-26 15:25 ` [PATCH 1/6] mm, oom: do not loop over all tasks if there are noexternal " Tetsuo Handa
2016-05-26 15:35 ` Michal Hocko
2016-05-26 16:14 ` [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external " Tetsuo Handa
2016-05-27 6:45 ` Michal Hocko
2016-05-27 7:15 ` Michal Hocko
2016-05-27 8:03 ` Michal Hocko
2016-05-26 12:40 ` [PATCH 2/6] proc, oom_adj: extract oom_score_adj setting into a helper Michal Hocko
2016-05-26 12:40 ` [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj Michal Hocko
2016-05-27 11:18 ` Michal Hocko
2016-05-27 16:18 ` Vladimir Davydov
2016-05-30 7:07 ` Michal Hocko
2016-05-30 8:47 ` Vladimir Davydov
2016-05-30 9:39 ` Michal Hocko
2016-05-30 10:26 ` Vladimir Davydov
2016-05-30 11:11 ` Michal Hocko
2016-05-30 12:19 ` Vladimir Davydov
2016-05-30 12:28 ` Michal Hocko [this message]
2016-05-26 12:40 ` [PATCH 4/6] mm, oom: skip over vforked tasks Michal Hocko
2016-05-27 16:48 ` Vladimir Davydov
2016-05-30 7:13 ` Michal Hocko
2016-05-30 9:52 ` Michal Hocko
2016-05-30 10:40 ` Vladimir Davydov
2016-05-30 10:53 ` Michal Hocko
2016-05-30 12:03 ` Michal Hocko
2016-05-26 12:40 ` [PATCH 5/6] mm, oom: kill all tasks sharing the mm Michal Hocko
2016-05-26 12:40 ` [PATCH 6/6] mm, oom: fortify task_will_free_mem Michal Hocko
2016-05-26 14:11 ` Tetsuo Handa
2016-05-26 14:23 ` Michal Hocko
2016-05-26 14:41 ` Tetsuo Handa
2016-05-26 14:56 ` Michal Hocko
2016-05-27 11:07 ` Michal Hocko
2016-05-27 16:00 ` [PATCH 0/5] Handle oom bypass more gracefully Michal Hocko
2016-05-30 13:05 [PATCH 0/6 -v2] " Michal Hocko
2016-05-30 13:05 ` [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj Michal Hocko
2016-05-31 7:41 ` Michal Hocko
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