linux-kernel - Re: [PATCH v3 3/8] mm/debug-pagealloc: make debug-pagealloc boottime configurable

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Message-Id: <20141124145542.08b97076.akpm@linux-foundation.org>
Date:	Mon, 24 Nov 2014 14:55:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>, Dave Hansen <dave@...1.net>,
	Michal Nazarewicz <mina86@...a86.com>,
	Jungsoo Son <jungsoo.son@....com>,
	Ingo Molnar <mingo@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/8] mm/debug-pagealloc: make debug-pagealloc
 boottime configurable

On Mon, 24 Nov 2014 17:15:21 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:

> Now, we have prepared to avoid using debug-pagealloc in boottime. So
> introduce new kernel-parameter to disable debug-pagealloc in boottime,
> and makes related functions to be disabled in this case.
> 
> Only non-intuitive part is change of guard page functions. Because
> guard page is effective only if debug-pagealloc is enabled, turning off
> according to debug-pagealloc is reasonable thing to do.
> 
> ...
>
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -858,6 +858,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			causing system reset or hang due to sending
>  			INIT from AP to BSP.
>  
> +	disable_debug_pagealloc
> +			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
> +			parameter allows user to disable it at boot time.
> +			With this parameter, we can avoid allocating huge
> +			chunk of memory for debug pagealloc and then
> +			the system will work mostly same with the kernel
> +			built without CONFIG_DEBUG_PAGEALLOC.
> +

Weren't we going to make this default to "off", require a boot option
to turn debug_pagealloc on?

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