linux-kernel - Re: [PATCH] Allow preemption during lazy mmu updates

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Date:	Sat, 28 Mar 2009 00:48:20 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Allow preemption during lazy mmu updates

On Fri, 2009-03-27 at 11:02 -0700, Jeremy Fitzhardinge wrote:
> Hi all,
> 
> We discussed this series a while ago.  The specific problem
> was the need to disable preemption in apply_to_pte_range when using
> lazy mmu updates around the callback function.  When used on usermode
> addresses there was no problem because it needs to take the pte
> lock anyway, but there's no requirement for taking a pte lock when
> updating kernel ptes, so it ended up adding a new no-preempt region.
> 
> The gist of the series is that if we get preempted while doing an mmu
> update, we flush all the pending updates and switch to the next task.
> We record that the task was doing a lazy mmu update in its task flags,
> and resume lazy updates when we switch back.
> 
> All the context-switch time activity happens in the existing
> context-switch pvops calls, so there's no cost to non-pvops systems,
> or to pvops backends which don't use lazy mmu updates.
> 
> I don't think there were any objections to this series, but Ingo would
> like to see an Acked by from someone since it gets into the mm side
> of things.
> 
> (The first patch in the series adds the required preempt disable/enable
> and then the rest of the series removes them again.  I think the first
> patch is already in mm-.)

Looks good from my POV

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

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