mm/thp: Preserve pgprot across huge page split

mm/thp: Preserve pgprot across huge page split

We're going to play games with page-protections, ensure we don't lose
them over a THP split.

Collapse seems to always allocate a new (huge) page which should
already end up on the new target node so loosing protections there
isn't a problem.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Paul Turner <pjt@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Link: http://lkml.kernel.org/n/tip-eyi25t4eh3l4cd2zp4k3bj6c@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>