From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: unit tests and get_user_pages_ptes_fast()
Date: Tue, 5 Oct 2010 16:15:47 +0200
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Cc: Avi Kivity <avi@redhat.com>, KVM list <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
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On Tue, Oct 05, 2010 at 06:22:17AM -0300, Marcelo Tosatti wrote:
> It'll not be so advantageous for ksm because there should be read-faults
> very rarely on that case.

It'll also make all clean swapcache dirty for no good.

> Will post.

If we've to walk pagetables twice, why don't you do this:

writable=1
get_user_pages_fast(write=write_fault)
if (!write_fault)
   writable = __get_user_pages_fast(write=1)

That will solve the debugging knob and it'll solve ksm and it'll be
optimal for read swapins on exclusive clean swapcache too.