mm/hugetlb: distinguish between migratability and movability

mm/hugetlb: distinguish between migratability and movability

Patch series "arm64/mm: Enable HugeTLB migration", v4.

This patch series enables HugeTLB migration support for all supported
huge page sizes at all levels including contiguous bit implementation.
Following HugeTLB migration support matrix has been enabled with this
patch series.  All permutations have been tested except for the 16GB.

           CONT PTE    PMD    CONT PMD    PUD
           --------    ---    --------    ---
  4K:         64K     2M         32M     1G
  16K:         2M    32M          1G
  64K:         2M   512M         16G

First the series adds migration support for PUD based huge pages.  It
then adds a platform specific hook to query an architecture if a given
huge page size is supported for migration while also providing a default
fallback option preserving the existing semantics which just checks for
(PMD|PUD|PGDIR)_SHIFT macros.  The last two patches enables HugeTLB
migration on arm64 and subscribe to this new platform specific hook by
defining an override.

The second patch differentiates between movability and migratability
aspects of huge pages and implements hugepage_movable_supported() which
can then be used during allocation to decide whether to place the huge
page in movable zone or not.

This patch (of 5):

During huge page allocation it's migratability is checked to determine
if it should be placed under movable zones with GFP_HIGHUSER_MOVABLE.
But the movability aspect of the huge page could depend on other factors
than just migratability.  Movability in itself is a distinct property
which should not be tied with migratability alone.

This differentiates these two and implements an enhanced movability check
which also considers huge page size to determine if it is feasible to be
placed under a movable zone.  At present it just checks for gigantic pages
but going forward it can incorporate other enhanced checks.

Link: http://lkml.kernel.org/r/1545121450-1663-2-git-send-email-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Suggested-by: Michal Hocko <mhocko@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>