From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id 2EFBC6B0006 for ; Thu, 18 Oct 2018 00:27:46 -0400 (EDT) Received: by mail-pf1-f199.google.com with SMTP id 25-v6so25312603pfs.5 for ; Wed, 17 Oct 2018 21:27:46 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id bd5-v6sor8938350plb.70.2018.10.17.21.27.44 for (Google Transport Security); Wed, 17 Oct 2018 21:27:44 -0700 (PDT) Date: Thu, 18 Oct 2018 13:27:39 +0900 From: Sergey Senozhatsky Subject: Re: [PATCH v3] mm: memcontrol: Don't flood OOM messages with no eligible task. Message-ID: <20181018042739.GA650@jagdpanzerIV> References: <20181017102821.GM18839@dhcp22.suse.cz> <20181017111724.GA459@jagdpanzerIV> <201810180246.w9I2koi3011358@www262.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201810180246.w9I2koi3011358@www262.sakura.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: Sergey Senozhatsky , Michal Hocko , Johannes Weiner , 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 , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , syzbot 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