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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, guro@fb.com,
	kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
	rientjes@google.com, yang.s@alibaba-inc.com,
	Andrew Morton <akpm@linux-foundation.org>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	syzbot <syzbot+77e6b28a7a7106ad0def@syzkaller.appspotmail.com>
Subject: Re: [PATCH v3] mm: memcontrol: Don't flood OOM messages with no eligible task.
Date: Thu, 18 Oct 2018 13:23:58 +0200	[thread overview]
Message-ID: <20181018112358.GB18839@dhcp22.suse.cz> (raw)
In-Reply-To: <6bbb0449-1f22-4d05-9e2a-636965b7dbc6@i-love.sakura.ne.jp>

On Thu 18-10-18 19:37:18, Tetsuo Handa wrote:
> On 2018/10/18 15:55, Michal Hocko wrote:
> > On Thu 18-10-18 11:46:50, Tetsuo Handa wrote:
> >> This is essentially a ratelimit approach, roughly equivalent with:
> >>
> >>   static DEFINE_RATELIMIT_STATE(oom_no_victim_rs, 60 * HZ, 1);
> >>   oom_no_victim_rs.flags |= RATELIMIT_MSG_ON_RELEASE;
> >>
> >>   if (__ratelimit(&oom_no_victim_rs)) {
> >>     dump_header(oc, NULL);
> >>     pr_warn("Out of memory and no killable processes...\n");
> >>     oom_no_victim_rs.begin = jiffies;
> >>   }
> > 
> > Then there is no reason to reinvent the wheel. So use the standard
> > ratelimit approach. Or put it in other words, this place is no special
> > to any other that needs some sort of printk throttling. We surely do not
> > want an ad-hoc solutions all over the kernel.
> 
> netdev_wait_allrefs() in net/core/dev.c is doing the same thing. Since
> out_of_memory() is serialized by oom_lock mutex, there is no need to use
> "struct ratelimit_state"->lock field. Plain "unsigned long" is enough.

That code probably predates generalized ratelimit api.

> > And once you realize that the ratelimit api is the proper one (put aside
> > any potential improvements in the implementation of this api) then you
> > quickly learn that we already do throttle oom reports and it would be
> > nice to unify that and ... we are back to a naked patch. So please stop
> > being stuborn and try to cooperate finally.
> 
> I don't think that ratelimit API is the proper one, for I am touching
> "struct ratelimit_state"->begin field which is not exported by ratelimit API.
> But if you insist on ratelimit API version, I can tolerate with below one.

I just give up. I do not really see why you always have to make the code
more complex than necessary and squash different things together. This
is a complete kernel code development antipattern.

I am not goging to reply to this thread more but let me note that this
is beyond fun in any aspect I can think off (and yeah I have considered
dark sense of humor as well).

> 
>  mm/oom_kill.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index f10aa53..7c6118e 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -1106,6 +1106,12 @@ bool out_of_memory(struct oom_control *oc)
>  	select_bad_process(oc);
>  	/* Found nothing?!?! */
>  	if (!oc->chosen) {
> +		static DEFINE_RATELIMIT_STATE(no_eligible_rs, 60 * HZ, 1);
> +
> +		ratelimit_set_flags(&no_eligible_rs, RATELIMIT_MSG_ON_RELEASE);
> +		if ((is_sysrq_oom(oc) || is_memcg_oom(oc)) &&
> +		    !__ratelimit(&no_eligible_rs))
> +			return false;
>  		dump_header(oc, NULL);
>  		pr_warn("Out of memory and no killable processes...\n");
>  		/*
> @@ -1115,6 +1121,7 @@ bool out_of_memory(struct oom_control *oc)
>  		 */
>  		if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
>  			panic("System is deadlocked on memory\n");
> +		no_eligible_rs.begin = jiffies;
>  	}
>  	if (oc->chosen && oc->chosen != (void *)-1UL)
>  		oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs

      reply	other threads:[~2018-10-18 11:24 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-17 10:06 Tetsuo Handa
2018-10-17 10:28 ` Michal Hocko
2018-10-17 11:17   ` Sergey Senozhatsky
2018-10-17 11:29     ` Michal Hocko
2018-10-18  2:46     ` Tetsuo Handa
2018-10-18  2:46       ` Tetsuo Handa
2018-10-18  4:27       ` Sergey Senozhatsky
2018-10-18  5:26         ` Tetsuo Handa
2018-10-18  5:26           ` Tetsuo Handa
2018-10-18  6:10           ` Sergey Senozhatsky
2018-10-18  7:56             ` Michal Hocko
2018-10-18  8:13               ` Sergey Senozhatsky
2018-10-18 11:58                 ` Tetsuo Handa
2018-10-18 23:54                   ` Sergey Senozhatsky
2018-10-19 10:35                     ` Tetsuo Handa
2018-10-19 10:35                       ` Tetsuo Handa
2018-10-23  0:47                       ` Sergey Senozhatsky
2018-10-23  8:37                       ` Petr Mladek
2018-10-23  8:54                         ` Michal Hocko
2018-10-18 14:30         ` Petr Mladek
2018-10-19  0:18           ` Tetsuo Handa
2018-10-23  8:21             ` Petr Mladek
2018-10-23 10:23               ` Tetsuo Handa
2018-10-18  6:55       ` Michal Hocko
2018-10-18 10:37         ` Tetsuo Handa
2018-10-18 11:23           ` Michal Hocko [this message]

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