Re: unit tests and get_user_pages_ptes_fast()

[Avi Kivity <avi@redhat.com>]

  On 10/05/2010 04:15 PM, Andrea Arcangeli wrote:
> 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.

But it means an extra vmexit in the following case:

- read fault
- page is present and writeable in the Linux page table

which is very common.  For this you need get_user_pages_ptes_fast().

-- 
error compiling committee.c: too many arguments to function