linux-kernel - Re: [patches] [PATCH] [28/34] i386: pte xchg optimization

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Date:	Wed, 2 May 2007 13:05:40 +0200
From:	Andi Kleen <ak@...ell.com>
To:	"Jan Beulich" <jbeulich@...ell.com>
Cc:	zach@...are.com, linux-kernel@...r.kernel.org, patches@...-64.org
Subject: Re: [patches] [PATCH] [28/34] i386: pte xchg optimization


> I always wondered why the xchg is necessary here at all. If the process of
> tearing down a page table entry has started, other users of the mapped
> linear address are broken anyway - why is it necessary to still monitor the
> effect they may have on the A/D bits, unless this is a transient tear down?
> 
> Checking for the uses of ptep_get_and_clear, I would judge that the use in
> change_pte_range() may in fact need the xchg, but the uses in
> vunmap_pte_range() and zap_pte_range() shouldn't.

Yes I agree. Might be a nice speed up for exit to distingush the cases.

-Andi
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