From: Jaroslav Kysela <perex@suse.cz>

The do_no_page() function in mm/memory.c does accounting for reserved pages
(++mm->rss), but in zap_pte_range() we don't decrement rss if the page was
reserved.

So don't account for PageReserved pages in the rss.  (Maybe it would be
better to fix zap_pte_range in the opposite direction..)