linux-kernel - Re: [PATCH] xen: avoid hypercalls when updating unpinned pud/pmd

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Message-ID: <20080602112508.GD18586@elte.hu>
Date:	Mon, 2 Jun 2008 13:25:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jan Beulich <jbeulich@...ell.com>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] xen: avoid hypercalls when updating unpinned pud/pmd


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> When operating on an unpinned pagetable (ie, one under construction or 
> destruction), it isn't necessary to use a hypercall to update a 
> pud/pmd entry.  Jan Beulich observed that a similar optimisation 
> avoided many thousands of hypercalls while doing a kernel build.
>
> One tricky part is that early in the kernel boot there's no page 
> structure, so we can't check to see if the page is pinned.  In that 
> case, we just always use the hypercall.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Cc: Jan Beulich <jbeulich@...ell.com>

applied to tip/x86/xen, thanks Jeremy.

	Ingo
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