linux-kernel - Re: [PATCH v2 0/7] Kernel huge I/O mapping support

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Message-ID: <20150224080927.GB19069@gmail.com>
Date:	Tue, 24 Feb 2015 09:09:27 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Toshi Kani <toshi.kani@...com>, 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 0/7] Kernel huge I/O mapping support

* Andrew Morton <akpm@...ux-foundation.org> wrote:

> <reads the code>
> 
> Oh.  We don't do any checking at all.  We're just telling 
> userspace programmers "don't do that".  hrm.  What are 
> your thoughts on adding the overlap checks to the kernel?

I have requested such sanity checking in previous review as 
well, it has to be made fool-proof for this optimization to 
be usable.

Another alternative would be to make this not a transparent 
optimization, but a separate API: ioremap_hugepage() or so.

The devices and drivers dealing with GBs of remapped pages 
is still relatively low, so they could make explicit use of 
the API and opt in to it.

What I was arguing against was to make it a CONFIG_ option: 
that achieves very little in practice, such APIs should be 
uniformly available.

Thanks,

	Ingo
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