One other fun thing.  I have a "victim" thread sitting in a loop doing:

	sleep(1)
	memcpy(&garbage, buffer, sz);

The "attacker" is doing

	madvise(buffer, sz, MADV_PAGEOUT);

in a loop.  That, oddly enough doesn't cause the victim to page fault.
But, if I do:

	memcpy(&garbage, buffer, sz);
	madvise(buffer, sz, MADV_PAGEOUT);

It *does* cause the memory to get paged out.  The MADV_PAGEOUT code
actually has a !pte_present() check.  It will punt on a PTE if it sees
it.  In other words, if a page is in the swap cache but not mapped by a
pte_present() PTE, MADV_PAGEOUT won't touch it.

Shouldn't MADV_PAGEOUT be able to find and reclaim those pages?  Patch
attached.