Reduce memory fragmentation to prevent page allocation failures

SLUB allocator is the default memory allocator since 2.6.23 and perform better than SLAB.
This should reduce memory fragmentation but as it can't be avoided, the compaction support could prevent page allocation failure when not enough contiguous pages are available to satisfy an allocation attempt.

The default raspberry pi kernel has been including these config options since a few months : https://github.com/raspberrypi/linux/pull/349

I built a kernel with this config (not using ABS though) and it's been working fine for several hours now where before it would have already logged many allocation failures.