From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Michal Hocko <mhocko@kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Qian Cai <cai@lca.pw>, Eric Dumazet <eric.dumazet@gmail.com>,
davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Date: Sat, 7 Sep 2019 20:00:34 +0900 [thread overview]
Message-ID: <28040332-4639-375a-0832-b47759d1d2d8@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20190904082540.GI3838@dhcp22.suse.cz>
On 2019/09/04 17:25, Michal Hocko wrote:
> On Wed 04-09-19 16:00:42, Sergey Senozhatsky wrote:
>> On (09/04/19 15:41), Sergey Senozhatsky wrote:
>>> But the thing is different in case of dump_stack() + show_mem() +
>>> some other output. Because now we ratelimit not a single printk() line,
>>> but hundreds of them. The ratelimit becomes - 10 * $$$ lines in 5 seconds
>>> (IOW, now we talk about thousands of lines).
>>
>> And on devices with slow serial consoles this can be somewhat close to
>> "no ratelimit". *Suppose* that warn_alloc() adds 700 lines each time.
>> Within 5 seconds we can call warn_alloc() 10 times, which will add 7000
>> lines to the logbuf. If printk() can evict only 6000 lines in 5 seconds
>> then we have a growing number of pending logbuf messages.
>
> Yes, ratelimit is problematic when the ratelimited operation is slow. I
> guess that is a well known problem and we would need to rework both the
> api and the implementation to make it work in those cases as well.
> Essentially we need to make the ratelimit act as a gatekeeper to an
> operation section - something like a critical section except you can
> tolerate more code executions but not too many. So effectively
>
> start_throttle(rate, number);
> /* here goes your operation */
> end_throttle();
>
> one operation is not considered done until the whole section ends.
> Or something along those lines.
Regarding OOM killer which is serialized by oom_lock mutex, I proposed
"mm, oom: More aggressively ratelimit dump_header()." at
https://lkml.kernel.org/r/1550325895-9291-2-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
but it was ignored.
>
> In this particular case we can increase the rate limit parameters of
> course but I think that longterm we need a better api.
>
I proposed "printk: Introduce "store now but print later" prefix." at
https://lkml.kernel.org/r/1550896930-12324-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
but it was not accepted.
But I think that more better solution for warn_alloc() is to defer printing
from allocating context (which may not be allowed to sleep) to WQ context.
I proposed "mm,oom: Defer dump_tasks() output." at
https://lkml.kernel.org/r/7de2310d-afbd-e616-e83a-d75103b986c6@i-love.sakura.ne.jp
and answered to Michal's concerns. I hope we can apply the same thing for
warn_alloc() and show_mem(). Then, we can minimize latency for both
"memory allocation failures" and "OOM killer invocations".
next prev parent reply other threads:[~2019-09-07 11:00 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 14:57 [PATCH] net/skbuff: silence warnings under memory pressure Qian Cai
2019-08-30 15:11 ` Eric Dumazet
2019-08-30 15:25 ` Qian Cai
2019-08-30 16:15 ` Eric Dumazet
2019-08-30 18:06 ` Qian Cai
2019-09-03 13:22 ` Michal Hocko
2019-09-03 15:42 ` Qian Cai
2019-09-03 18:53 ` Michal Hocko
2019-09-03 21:42 ` Qian Cai
2019-09-04 6:15 ` Michal Hocko
2019-09-04 6:41 ` Sergey Senozhatsky
2019-09-04 6:54 ` Michal Hocko
2019-09-04 7:19 ` Sergey Senozhatsky
2019-09-04 7:43 ` Sergey Senozhatsky
2019-09-04 12:14 ` Qian Cai
2019-09-04 14:48 ` Sergey Senozhatsky
2019-09-04 15:07 ` Qian Cai
2019-09-04 20:42 ` Qian Cai
2019-09-05 8:32 ` Eric Dumazet
2019-09-05 14:09 ` Qian Cai
2019-09-05 15:06 ` Eric Dumazet
2019-09-05 15:14 ` Eric Dumazet
2019-09-05 11:32 ` Sergey Senozhatsky
2019-09-05 16:03 ` Qian Cai
2019-09-05 17:14 ` Steven Rostedt
2019-09-06 2:50 ` Sergey Senozhatsky
2019-09-06 4:32 ` Sergey Senozhatsky
2019-09-06 21:17 ` Qian Cai
2019-09-05 17:23 ` Steven Rostedt
2019-09-06 3:39 ` Sergey Senozhatsky
2019-09-06 15:32 ` Petr Mladek
2019-09-09 1:10 ` Sergey Senozhatsky
2019-09-06 14:55 ` Petr Mladek
2019-09-06 19:51 ` Sergey Senozhatsky
2019-11-14 17:12 ` Qian Cai
2019-11-18 15:27 ` Petr Mladek
2019-11-19 0:41 ` Sergey Senozhatsky
2019-11-19 9:41 ` Petr Mladek
2019-11-19 15:58 ` Qian Cai
2019-11-20 1:30 ` Sergey Senozhatsky
2019-11-20 16:13 ` Petr Mladek
2019-11-21 1:05 ` Sergey Senozhatsky
2019-11-21 9:15 ` Petr Mladek
2019-09-04 7:00 ` Sergey Senozhatsky
2019-09-04 8:25 ` Michal Hocko
2019-09-04 11:59 ` Qian Cai
2019-09-04 12:07 ` Michal Hocko
2019-09-04 12:28 ` Qian Cai
2019-09-07 11:00 ` Tetsuo Handa [this message]
2019-09-04 6:15 ` Michal Hocko
2019-09-02 14:24 ` Vlastimil Babka
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