linux-kernel - Re: [patch 1/3] mmu

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Message-ID: <20080201035249.GE26420@sgi.com>
Date:	Thu, 31 Jan 2008 21:52:49 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrea Arcangeli <andrea@...ranet.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 1/3] mmu_notifier: Core code

> Index: linux-2.6/include/linux/mmu_notifier.h
...
> +struct mmu_notifier_ops {
...
> +	/*
> +	 * invalidate_range_begin() and invalidate_range_end() must paired.
> +	 * Multiple invalidate_range_begin/ends may be nested or called
> +	 * concurrently. That is legit. However, no new external references
> +	 * may be established as long as any invalidate_xxx is running or
> +	 * any invalidate_range_begin() and has not been completed through a
> +	 * corresponding call to invalidate_range_end().
> +	 *
> +	 * Locking within the notifier needs to serialize events correspondingly.
> +	 *
> +	 * If all invalidate_xx notifier calls take a driver lock then it is possible
> +	 * to run follow_page() under the same lock. The lock can then guarantee
> +	 * that no page is removed. That way we can avoid increasing the refcount
> +	 * of the pages.
> +	 *
> +	 * invalidate_range_begin() must clear all references in the range
> +	 * and stop the establishment of new references.
> +	 *
> +	 * invalidate_range_end() reenables the establishment of references.
> +	 *
> +	 * atomic indicates that the function is called in an atomic context.
> +	 * We can sleep if atomic == 0.
> +	 */
> +	void (*invalidate_range_begin)(struct mmu_notifier *mn,
> +				 struct mm_struct *mm,
> +				 unsigned long start, unsigned long end,
> +				 int atomic);
> +
> +	void (*invalidate_range_end)(struct mmu_notifier *mn,
> +				 struct mm_struct *mm, int atomic);

I think we need to pass in the same start-end here as well.  Without it,
the first invalidate_range would have to block faulting for all addresses
and would need to remain blocked until the last invalidate_range has
completed.  While this would work, (and will probably be how we implement
it for the short term), it is far from ideal.

Thanks,
Robin
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