linux-kernel - Re: [PATCH] mm: remove global locks from mm/highmem.c

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Message-Id: <20070129174118.0e922ab3.akpm@osdl.org>
Date:	Mon, 29 Jan 2007 17:41:18 -0800
From:	Andrew Morton <akpm@...l.org>
To:	"Martin J. Bligh" <mbligh@...igh.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] mm: remove global locks from mm/highmem.c

On Mon, 29 Jan 2007 17:31:20 -0800
"Martin J. Bligh" <mbligh@...igh.org> wrote:

> Peter Zijlstra wrote:
> > On Sun, 2007-01-28 at 14:29 -0800, Andrew Morton wrote:
> > 
> >> As Christoph says, it's very much preferred that code be migrated over to
> >> kmap_atomic().  Partly because kmap() is deadlockable in situations where a
> >> large number of threads are trying to take two kmaps at the same time and
> >> we run out.  This happened in the past, but incidences have gone away,
> >> probably because of kmap->kmap_atomic conversions.
> > 
> >> From which callsite have you measured problems?
> > 
> > CONFIG_HIGHPTE code in -rt was horrid. I'll do some measurements on
> > mainline.
> > 
> 
> CONFIG_HIGHPTE is always horrid -we've known that for years.

We have?  What's wrong with it?  <looks around for bug reports>

> Don't use it.
> 
> If that's all we're fixing here, I'd be highly suspect ...

highpte uses atomic kmaps - it is unrelated to this work.
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