linux-kernel - Re: [PATCH V2] mm: add a new command-line kmemcheck value

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Message-ID: <53035433.3000405@huawei.com>
Date:	Tue, 18 Feb 2014 20:38:11 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	"Vegard Nossum" <vegardno@....uio.no>,
	Pekka Enberg <penberg@...nel.org>,
	Mel Gorman <mgorman@...e.de>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>, Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH V2] mm: add a new command-line kmemcheck value

On 2014/2/18 18:28, Vegard Nossum wrote:

> On 17 February 2014 03:34, Xishi Qiu <qiuxishi@...wei.com> wrote:
>> If we want to debug the kernel memory, we should turn on CONFIG_KMEMCHECK
>> and rebuild the kernel. This always takes a long time and sometimes
>> impossible, e.g. users don't have the kernel source code or the code
>> is different from "www.kernel.org" (private features may be added to the
>> kernel, and usually users can not get the whole code).
>>
>> This patch adds a new command-line "kmemcheck=3", then the kernel will run
>> as the same as CONFIG_KMEMCHECK=off even CONFIG_KMEMCHECK is turn on.
>> "kmemcheck=0/1/2" is the same as originally. This means we can always turn
>> on CONFIG_KMEMCHECK, and use "kmemcheck=3" to control it on/off with out
>> rebuild the kernel.
>>
>> In another word, "kmemcheck=3" is equivalent:
>> 1) turn off CONFIG_KMEMCHECK
>> 2) rebuild the kernel
>> 3) reboot
>>
>> The different between kmemcheck=0 and 3 is the used memory and nr_cpus.
>> Also kmemcheck=0 can used in runtime, and kmemcheck=3 is only used in boot.
>> boottime: kmemcheck=0/1/2/3 (command-line)
>> runtime: kmemcheck=0/1/2 (/proc/sys/kernel/kmemcheck)
> 
> This is not the right way to do what you want.
> 
> The behaviour that we want is:
> 
>  - CONFIG_KMEMCHECK=y + kmemcheck=0 (boot parameter) should have a
> minimal runtime impact and not limit the number of CPUs
>  - CONFIG_KMEMCHECK=y + kmemcheck=1 should limit the number of CPUs during boot
>  - setting kmemcheck to 1 via /proc/sys/kernel/kmemcheck should
> probably return an error if more than 1 CPU is online
> 
> 
> Vegard
> 

Hi Vegard,

Thank you for your reply. If we only use "kmemcheck=0" to control, how about
the used memory? Will it use about twice as much memory as normal?

Thanks,
Xishi Qiu

> .
> 



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