Patch series "mm: PG_reserved cleanups and documentation", v2.

I was recently going over all users of PG_reserved.  Short story: it is
difficult and sometimes not really clear if setting/checking for
PG_reserved is only a relict from the past.  Easy to break things.  I
guess I now have a pretty good idea wh things are like that nowadays and
how they evolved.

I had way more cleanups in this series inititally, but some
architectures take PG_reserved as a way to apply a different caching
strategy (for MMIO pages).  So I decided to only include the most
obvious changes (that are less likely to break something).  So the big
chunk of manual SetPageReserved users are MMIO/DMA related things on
device buffers.

Most notably, for device memory we will hopefully soon stop setting
PG_reserved.  Then the documentation has to be updated.

This patch (of 9):

The l1 GATT page table is kept in a special on-chip page with 64
entries.  We allocate the l2 page table pages via get_zeroed_page() and
enter them into the table.  These l2 pages are modified accordingly when
inserting/removing memory via efficeon_insert_memory and
efficeon_remove_memory.

Apart from that, these pages are not exposed or ioremap'ed.  We can stop
setting them reserved (propably copied from generic code).

Link: http://lkml.kernel.org/r/20190114125903.24845-2-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>