From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Michal Hocko <mhocko@kernel.org>,
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 13:27:39 +0900 [thread overview]
Message-ID: <20181018042739.GA650@jagdpanzerIV> (raw)
In-Reply-To: <201810180246.w9I2koi3011358@www262.sakura.ne.jp>
On (10/18/18 11:46), Tetsuo Handa wrote:
> Sergey Senozhatsky wrote:
> >
> > int printk_ratelimit_interval(void)
> > {
> > int ret = DEFAULT_RATELIMIT_INTERVAL;
> > struct tty_driver *driver = NULL;
> > speed_t min_baud = MAX_INT;
> >
> > console_lock();
> > for_each_console(c) {
> > speed_t br;
> >
> > if (!c->device)
> > continue;
> > if (!(c->flags & CON_ENABLED))
> > continue;
> > if (!c->write)
> > continue;
> > driver = c->device(c, index);
> > if (!driver)
> > continue;
> >
> > br = tty_get_baud_rate(tty_driver to tty_struct [???]);
> > min_baud = min(min_baud, br);
> > }
> > console_unlock();
> >
> > switch (min_baud) {
> > case 115200:
> > return ret;
> >
> > case ...blah blah...:
> > return ret * 2;
> >
> > case 9600:
> > return ret * 4;
> > }
> > return ret;
> > }
>
> I don't think that baud rate is relevant. Writing to console messes up
> operations by console users. What matters is that we don't mess up consoles
> to the level (or frequency) where console users cannot do their operations.
> That is, interval between the last moment we wrote to a console and the
> first moment we will write to a console for the next time matters. Roughly
> speaking, remember the time stamp when we called call_console_drivers() for
> the last time, and compare with that stamp before trying to call a sort of
> ratelimited printk(). My patch is doing it using per call-site stamp recording.
To my personal taste, "baud rate of registered and enabled consoles"
approach is drastically more relevant than hard coded 10 * HZ or
60 * HZ magic numbers... But not in the form of that "min baud rate"
brain fart, which I have posted.
What I'd do:
-- Iterate over all registered and enabled serial consoles
-- Sum up all the baud rates
-- Calculate (*roughly*) how many bytes per second/minute/etc my
call_console_driver() can push
-- we actually don't even have to iterate all consoles. Just
add a baud rate in register_console() and sub baud rate
in unregister_console() of each console individually
-- and have a static unsigned long in printk.c, which OOM
can use in rate-limit interval check
-- Leave all the noise behind: e.g. console_sem can be locked by
a preempted fbcon, etc. It's out of my control; bad luck, there
is nothing I can do about it.
-- Then I would, probably, take the most recent, say, 100 OOM
reports, and calculate the *average* strlen() value
(including \r and \n at the end of each line)
(strlen(oom_report1) + ... + strlen(omm_report100)) / 100
Then I'd try to reach an agreement with MM people that we will
use this "average" oom_report_strlen() in ratelimit interval
calculation. Yes, some reports will be longer, some shorter.
Say, suppose...
I have 2 consoles, and I can write 250 bytes per second.
And average oom_report is 5000 bytes.
Then I can print one oom_report every (5000 / 250) seconds
in the *best* case. That's the optimistic baseline. There
can be printk()-s from other CPUs, etc. etc. No one can
predict those things.
Note, how things change when I have just 1 console enabled.
I have 1 console, and I can write 500 bytes per second.
And average oom_report is 5000 bytes.
Then I can print one oom_report every (5000 / 500) seconds
in the *best* case.
Just my $0.02. Who knows, may be it's dumb and ugly.
I don't have a dog in this fight.
-ss
next prev parent reply other threads:[~2018-10-18 4:27 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-17 10:06 [PATCH v3] mm: memcontrol: Don't flood OOM messages with no eligible task 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 4:27 ` Sergey Senozhatsky [this message]
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
2018-10-23 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
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