mm: migrate: remove THP mapcount check in numamigrate_isolate_page()

mainline inclusion
from mainline-v6.7-rc1
commit 728be28fae8c838d52c91dce4867133798146357
category: other
bugzilla: https://gitee.com/openeuler/kernel/issues/I8JQWQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=728be28fae8c838d52c91dce4867133798146357

--------------------------------

The check of THP mapped by multiple processes was introduced by commit
04fa5d6a ("mm: migrate: check page_count of THP before migrating") and
refactor by commit 340ef390 ("mm: numa: cleanup flow of transhuge page
migration"), which is out of date, since migrate_misplaced_page() is now
using the standard migrate_pages() for small pages and THPs, the reference
count checking is in folio_migrate_mapping(), so let's remove the special
check for THP.

Link: https://lkml.kernel.org/r/20230913095131.2426871-3-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>