From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Michal Hocko <mhocko@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Petr Mladek <pmladek@suse.com>,
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: Tue, 28 Apr 2020 22:11:19 +0900 [thread overview]
Message-ID: <b4d74234-8009-9ffd-011f-bd5d1a4b85f6@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20200428121828.GP28637@dhcp22.suse.cz>
On 2020/04/28 21:18, Michal Hocko wrote:
> On Tue 28-04-20 20:33:21, Tetsuo Handa wrote:
>> On 2020/04/27 15:21, Sergey Senozhatsky wrote:
>>>> KERN_NO_CONSOLES is for type of messages where "saved for later analysis" is
>>>> important but "printed for immediate notification" is not important.
>>>> In other words, KERN_NO_CONSOLES is NOT for dying messages where "printed for
>>>> immediate notification" is important.
>>>
>>> per-console loglevel is a user configurable parameter.
>>> KERN_NO_CONSOLES is a hard-coded policy.
>>
>> But given that whether to use KERN_NO_CONSOLES is configurable via e.g. sysctl,
>> KERN_NO_CONSOLES will become a user configurable parameter. What's still wrong?
>
> How do I as a kernel developer know that KERN_NO_CONSOLES should be
> used? In other words, how can I assume what a user will consider
> important on the console?
>
Existing KERN_$LEVEL allows a user to determine whether he/she wants that message
to be printed on consoles (even if it spams his/her operation doing on consoles), and
at the same time constrains that user whether that message is saved to log files.
KERN_NO_CONSOLES allows a user to control whether he/she wants that message to be
saved to log files (without spamming his/her operation doing on consoles).
Consoles which are limited by "rows" * "columns" size should receive (ideally) up to
a few lines of messages. Printing more lines on such consoles disturbs users using
such consoles. Let alone printing one thousand lines of messages (e.g. dump_tasks())
on such consoles. Printing one thousand lines of messages on read-only consoles (e.g.
netconsole) might be fine, but non-urgent messages can afford waiting for userspace
to do more sophisticated handling (e.g. evaluate and filter).
Even without per-console loglevel feature, we can reduce spam messages for consoles
by using KERN_NO_CONSOLES. For example, send only the summary part of OOM-killer and
allocation failure messages to both consoles and log files (by not using KERN_NO_CONSOLES),
and send the non-summary part to only log files (by using KERN_NO_CONSOLES with
KERN_$LEVEL used for summary part in order to make sure that userspace daemon will
save both the summary and non-summary parts).
next prev parent reply other threads:[~2020-04-28 13:12 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 [this message]
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
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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