linux-kernel - Could we do immediate pte zaps in vunmap?

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Date:	Fri, 26 Nov 2010 00:10:51 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Nick Piggin <npiggin@...nel.dk>
CC:	"Xen-devel@...ts.xensource.com" <Xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Could we do immediate pte zaps in vunmap?

What if vm_unmap_ram() and co. immediately zeroed out the ptes, but
lazily deferred the tlb flushes?  It seems to me there's no benefit in
batching up the pte clearing since that can't be amortized like the tlb
flush.

I think that would solve the problem we have with the interactions
between lazy unmap and Xen.  The issue is having stray pte entries
around (because Xen keeps track of those as part of its page-type
mechanism), but stale tlb entries are no problem.

Thanks,
    J
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