mm: cma: adjust address limit to avoid hitting low/high memory boundary

mm: cma: adjust address limit to avoid hitting low/high memory boundary

Russell King recently noticed that limiting default CMA region only to low
memory on ARM architecture causes serious memory management issues with
machines having a lot of memory (which is mainly available as high
memory).  More information can be found the following thread:
http://thread.gmane.org/gmane.linux.ports.arm.kernel/348441/

Those two patches removes this limit letting kernel to put default CMA
region into high memory when this is possible (there is enough high memory
available and architecture specific DMA limit fits).

This should solve strange OOM issues on systems with lots of RAM (i.e.
>1GiB) and large (>256M) CMA area.

This patch (of 2):

Automatically allocated regions should not cross low/high memory boundary,
because such regions cannot be later correctly initialized due to spanning
across two memory zones.  This patch adds a check for this case and a
simple code for moving region to low memory if automatically selected
address might not fit completely into high memory.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Daniel Drake <drake@endlessm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>