linux-kernel - Re: [PATCH v2 6/7] x86, mm: Support huge I/O mappings on x86

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Date:	Wed, 18 Feb 2015 21:44:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, arnd@...db.de, linux-mm@...ck.org,
	x86@...nel.org, linux-kernel@...r.kernel.org, Elliott@...com
Subject: Re: [PATCH v2 6/7] x86, mm: Support huge I/O mappings on x86


* Toshi Kani <toshi.kani@...com> wrote:

> This patch implements huge I/O mapping capability interfaces on x86.

> +#ifdef CONFIG_HUGE_IOMAP
> +#ifdef CONFIG_X86_64
> +#define IOREMAP_MAX_ORDER       (PUD_SHIFT)
> +#else
> +#define IOREMAP_MAX_ORDER       (PMD_SHIFT)
> +#endif
> +#endif  /* CONFIG_HUGE_IOMAP */

> +#ifdef CONFIG_HUGE_IOMAP

Hm, so why is there a Kconfig option for this? It just 
complicates things.

For example the kernel already defaults to mapping itself 
with as large mappings as possible, without a Kconfig entry 
for it. There's no reason to make this configurable - and 
quite a bit of complexity in the patches comes from this 
configurability.

Thanks,

	Ingo
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