mm, thp, migrate: handling migration of 64KB hugepages

mm, thp, migrate: handling migration of 64KB hugepages

When a 64KB hugepage is migrated, it should be properly
handled since it is different from other normal page
mappings. The kernel should handle a set of sequential
16 page mappings at once. If not, the kernel can mishandle
map counts of a compound page (that is, a set of pages).
It can be a source of kernel bugs and the bug is easily
reproduced on low-memory devices.

This patch deals with the migration of 64KB hugepages.

Fixes: 90eb23660fef ('mm: THP: introducing a fine-grained transparent hugepage technique for ARM64 architecture')
Change-Id: I50a5d4e9a263e7dcbded15c982f57c15a3a48f39
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>