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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Michal Hocko <mhocko@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org, Dmitry Safonov <dima@arista.com>,
	Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".
Date: Wed, 13 May 2020 20:03:53 +0900	[thread overview]
Message-ID: <20564555-7b84-f716-5dcd-978f76ad459a@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20200513100413.GH17734@linux-b0ei>

On 2020/05/13 19:04, Petr Mladek wrote:
>> What is wrong with adding NO_CONSOLES ?
> 
> How does it differ from KERN_DEBUG? The debug messages:
> 
>   + can be disabled via sysfs
>   + might reach console when this loglevel is enabled

KERN_NO_CONSOLES is different from KERN_DEBUG in that KERN_NO_CONSOLES
itself does not affect userspace daemon's judgement (whether to filter
KERN_$LOGLEVEL messages).

> What is so special about  OOM dump task so that it would deserve such
> complications?

OOM dump task is special in that it can generate thousands of KERN_INFO
messages. If such messages are printed to consoles, it defers solving OOM
situation.

But setting /proc/sys/vm/oom_dump_tasks to 0 causes such messages being
not delivered to userspace daemon for later analysis. Therefore, we can not
set /proc/sys/vm/oom_dump_tasks to 0 if we want to save such messages for
later analysis.

Changing console loglevel (e.g. setting "quiet" kernel command line option)
in order to hide such messages also prevents all other KERN_INFO messages from
being printed to consoles. Since some KERN_INFO messages are worth printing to
consoles while other KERN_INFO messages are worth printing to consoles,
controlling with

>   + loglevel assigned to each message

is inevitable.

I think that basically only oops (e.g. WARN()/BUG()/panic()) messages worth
printing to consoles and the rest messages do not worth printing to consoles.
Existing KERN_$LOGLEVEL is too rough-grained.


  parent reply	other threads:[~2020-05-13 11:04 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24  2:42 [PATCH] printk: Add loglevel for "do not print to consoles" Tetsuo Handa
2020-04-24 13:28 ` Steven Rostedt
2020-04-24 14:00   ` Tetsuo Handa
2020-04-24 14:31     ` Steven Rostedt
2020-04-24 15:28       ` Tetsuo Handa
2020-04-24 15:42         ` Steven Rostedt
2020-04-24 15:52           ` Dmitry Safonov
2020-04-24 16:10           ` Tetsuo Handa
2020-04-24 16:21             ` Steven Rostedt
2020-04-24 16:34               ` Tetsuo Handa
2020-04-25  0:46 ` Sergey Senozhatsky
2020-04-25  1:07   ` Tetsuo Handa
2020-04-27  6:21     ` Sergey Senozhatsky
2020-04-28 11:33       ` Tetsuo Handa
2020-04-28 12:18         ` Michal Hocko
2020-04-28 13:11           ` Tetsuo Handa
2020-04-28 15:45             ` Michal Hocko
2020-04-28 16:23               ` Tetsuo Handa
2020-04-29 14:21                 ` Michal Hocko
2020-04-29 16:35                   ` Tetsuo Handa
2020-05-13  6:26                     ` Sergey Senozhatsky
2020-05-13  7:58                       ` Tetsuo Handa
2020-05-13 10:04                         ` Petr Mladek
2020-05-13 10:49                           ` Michal Hocko
2020-05-13 11:24                             ` Tetsuo Handa
2020-05-13 12:19                               ` Petr Mladek
2020-05-13 12:59                                 ` Tetsuo Handa
2020-05-14  8:00                                   ` Petr Mladek
2020-05-14 11:23                                     ` Tetsuo Handa
2020-05-14 16:26                                       ` Petr Mladek
2020-05-14 23:24                                         ` Tetsuo Handa
2020-05-13 11:03                           ` Tetsuo Handa [this message]
2020-05-13 12:34                             ` Petr Mladek
2020-05-13 13:46                             ` Steven Rostedt
2020-05-13 14:03                               ` Tetsuo Handa
2020-05-13 13:55                             ` Steven Rostedt
2020-05-13 15:20                               ` Tetsuo Handa
2020-05-06  9:45         ` Tetsuo Handa
2020-05-06 15:26           ` Joe Perches
2020-05-07  0:50             ` Tetsuo Handa
2020-05-07  1:02               ` Joe Perches
2020-05-07  5:13                 ` Tetsuo Handa
2020-05-07  5:30                   ` Joe Perches
2020-05-07  5:39                     ` Tetsuo Handa

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