linux-kernel - Re: [PATCH 2/2] x86,mm,64bit: Round up memory boundary for init_memory_mapping

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Date:	Fri, 25 Feb 2011 11:03:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86,mm,64bit: Round up memory boundary for
 init_memory_mapping_high()


* Yinghai Lu <yinghai@...nel.org> wrote:

>  init_memory_mapping_active_regions(unsigned long start, unsigned long end)
>  {
>  	struct mapping_work_data data;
> +	int use_gbpages;
> +
> +	/* see init_memory_mapping() for the setting */
> +#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK)
> +	use_gbpages = 0;
> +#else
> +	use_gbpages = direct_gbpages;
> +#endif

Sigh. You should *never* ever even think about writing such code. It only results in 
crap, and in crap duplicated elsewhere as well:

if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KMEMCHECK)
        /*
         * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
         * This will simplify cpa(), which otherwise needs to support splitting
         * large pages into small in interrupt context, etc.
         */
        use_pse = use_gbpages = 0;
#else
        use_pse = cpu_has_pse;
        use_gbpages = direct_gbpages;
#endif

Thanks,

	Ingo
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