On 2020/04/29 0:45, Michal Hocko wrote:
> On Tue 28-04-20 22:11:19, Tetsuo Handa wrote:
>> Existing KERN_$LEVEL allows a user to determine whether he/she wants that
>> message
>> to be printed on consoles (even if it spams his/her operation doing on
>> consoles), and
>> at the same time constrains that user whether that message is saved to log
>> files.
>> KERN_NO_CONSOLES allows a user to control whether he/she wants that message
>> to be
>> saved to log files (without spamming his/her operation doing on consoles).
>
> I understand that. But how do I know whether the user considers the
> particular information important enough to be dumped on the console.
> This sounds like a policy in the kernel to me.
I'm still unable to understand your question.
> I simply cannot forsee
> any console configuration to tell whether my information is going to
> swamp the console to no use or not.
Neither can I.
> Compare that to KERN_$LEVEL instead.
> I know that an information is of low/high importance. It is the user
> policy to decide and base some filtering on top of that priority.
Whether to use KERN_NO_CONSOLES is not per-importance basis but per-content
basis.
Since both pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n", ...)
from dump_tasks() and
pr_info("oom-kill:constraint=%s,nodemask=%*pbl", ...) from dump_oom_summary()
use KERN_INFO importance,
existing KERN_$LEVEL-based approach cannot handle these messages differently.
Since changing the former to
e.g. KERN_DEBUG will cause userspace to discard the messages, we effectively
can't change KERN_$LEVEL.
If the kernel allows the former to use KERN_NO_CONSOLES in addition to
KERN_INFO, the administrator can
select from two choices: printing "both the former and the latter" or "only the
latter" to consoles.
