autonuma: shrink the per-page page_autonuma struct size
From 32 to 12 bytes, so the AutoNUMA memory footprint is reduced to
0.29% of RAM.
This however will fail to migrate pages above a 16 Terabyte offset
from the start of each node (migration failure isn't fatal, simply
those pages will not follow the CPU, a warning will be printed in the
log just once in that case).
AutoNUMA will also fail to build if there are more than (2**15)-1
nodes supported by the MAX_NUMNODES at build time (it would be easy to
relax it to (2**16)-1 nodes without increasing the memory footprint,
but it's not even worth it, so let's keep the negative space reserved
for now).
This means the max RAM configuration fully supported by AutoNUMA
becomes AUTONUMA_LIST_MAX_PFN_OFFSET multiplied by 32767 nodes
multiplied by the PAGE_SIZE (assume 4096 here, but for some archs it's
bigger).
4096*32767*(0xffffffff-3)>>(10*5) = 511 PetaBytes.
8 files changed
