linux-kernel - Re: [RFC PATCH] ARM: mm: disable kmap_high

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Date:	Tue, 5 Mar 2013 17:36:12 +0800 (HKT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ARM: mm: disable kmap_high_get() for SMP

On Mon, 4 Mar 2013, Joonsoo Kim wrote:

> With SMP and enabling kmap_high_get(), it makes users of kmap_atomic()
> sequential ordered, because kmap_high_get() use global kmap_lock().
> It is not welcome situation, so turn off this optimization for SMP.

I'm not sure I understand the problem.

The lock taken by kmap_high_get() is released right away before that 
function returns and therefore this is not actually serializing 
anything.


Nicolas
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