Documentation/driver-api/cxl: remove page-allocator quirk section

will fallback to allocate from :code:`ZONE_NORMAL`.

Zone and Node Quirks

====================

Let's consider a configuration where the local DRAM capacity is largely onlined

into :code:`ZONE_NORMAL`, with no :code:`ZONE_MOVABLE` capacity present. The

CXL capacity has the opposite configuration - all onlined in

:code:`ZONE_MOVABLE`.

Under the default allocation policy, the page allocator will completely skip

:code:`ZONE_MOVABLE` as a valid allocation target.  This is because, as of

Linux v6.15, the page allocator does (approximately) the following: ::

  for (each zone in local_node):

    for (each node in fallback_order):

      attempt_allocation(gfp_flags);

Because the local node does not have :code:`ZONE_MOVABLE`, the CXL node is

functionally unreachable for direct allocation.  As a result, the only way

for CXL capacity to be used is via `demotion` in the reclaim path.

This configuration also means that if the DRAM ndoe has :code:`ZONE_MOVABLE`

capacity - when that capacity is depleted, the page allocator will actually

prefer CXL :code:`ZONE_MOVABLE` pages over DRAM :code:`ZONE_NORMAL` pages.

We may wish to invert this priority in future Linux versions.

If `demotion` and `swap` are disabled, Linux will begin to cause OOM crashes

when the DRAM nodes are depleted. See the reclaim section for more details.

CGroups and CPUSets

===================

Finally, assuming CXL memory is reachable via the page allocation (i.e. onlined