[$] Preserving the mobility of ZONE_MOVABLE

Memory fragmentation has long been a problem for Linux systems, to the
point that, for years, finding even two physically contiguous pages was an
uncertain affair. That said, the situation has improved considerably in
the last decade or so thanks to a number of changes implemented by the
memory-management developers. One of those changes is the creation of
'movable'
memory zones where pages can be relocated if need be. All that work is for
nothing, though, if somebody comes along and pins down a page in one of
these movable zones. This
patch set from Pavel Tatashin seeks to prevent that from happening, but
may risk creating problems elsewhere.