linux-kernel - Re: [PATCH] Proposed update to the kernel kmap/kunmap API

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Message-Id: <20060806124827.7f0e1993.akpm@osdl.org>
Date:	Sun, 6 Aug 2006 12:48:27 -0700
From:	Andrew Morton <akpm@...l.org>
To:	James Bottomley <James.Bottomley@...elEye.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Proposed update to the kernel kmap/kunmap API

On Sun, 06 Aug 2006 10:01:55 -0500
James Bottomley <James.Bottomley@...elEye.com> wrote:

> The simple part of the proposal is to give non-highmem architectures
> access to the kmap API for the purposes of overriding (this is what the
> attached patch does).
> 
> The more controversial part of the proposal is that we should now
> require all architectures with coherence issues to manage data coherence
> via the kmap/kunmap API.  Thus driver writers never have to write code
> like

kmap() is a nasty thing.  It has theoretical deadlock problems (which used
to be real ones back in the 2.4 days) and the present implementation uses a
kernel-wide lock.

We've been gradually and sporadically working to make kmap() go away, so
please let's not do anything which encourages its use.

kmap_atomic() is much preferred.  Can this initiative be recast around
kmap_atomic()?
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