linux-kernel - Re: [PATCH v2 2/2] init/Kconfig: Increase default log buffer size from 128 KB to 512 KB

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Date:   Thu, 29 Oct 2020 23:16:01 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org,
        John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-embedded@...r.kernel.org
Subject: Re: [PATCH v2 2/2] init/Kconfig: Increase default log buffer size
 from 128 KB to 512 KB

Dear Petr,


Am 11.08.20 um 12:53 schrieb Petr Mladek:
> On Tue 2020-08-11 11:29:24, Paul Menzel wrote:
>> Commit f17a32e97e (let LOG_BUF_SHIFT default to 17) from 2008 was the
>> last time, the the default log buffer size bump was increased.
>>
>> Machines have evolved, and on current hardware, enough memory is
>> present, and some devices have over 200 PCI devices, like a two socket
>> Skylake-E server, resulting a lot of lines.
>>
>> Therefore, increase the default from 128 KB to 512 KB. Anyone, with
>> limited memory, can still lower it.
>>
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -681,9 +681,9 @@ config IKHEADERS
>>   	  kheaders.ko is built which can be loaded on-demand to get access to headers.
>>   
>>   config LOG_BUF_SHIFT
>> -	int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
>> +	int "Kernel log buffer size (17 => 128KB, 19 => 512KB)"
>>   	range 12 25
>> -	default 17
>> +	default 19
>>   	depends on PRINTK
>>   	help
>>   	  Select the minimal kernel log buffer size as a power of 2.
> 
> Honestly, I do not have experience with changing the defaults. People
> hacking small devices might complain. Well, this can be solved
> by increasing the default only when BASE_FULL is set.
> 
> I am personally fine with increasing the default when BASE_FULL
> is set. The amount of messages is growing over time because of
> increasing complexity of both the hardware and software.
> Fortunately also the amount of available memory is growing.
> 
> Well, this should get discussed in wider audience. Adding some
> people into CC.
> 
> JFYI, it started with report of lost messages, see
> https://lore.kernel.org/lkml/264bfbae-122d-9c41-59ea-6413f91bd866@molgen.mpg.de/

As there was no objection, is it possible to apply the two patches, and 
maybe even get them into Linux 5.10?


Kind regards,

Paul