BACKPORT: mm: add per-order mTHP split counters

Patch series "mm: introduce per-order mTHP split counters", v3.

At present, the split counters in THP statistics no longer include
PTE-mapped mTHP.  Therefore, we want to introduce per-order mTHP split
counters to monitor the frequency of mTHP splits.  This will assist
developers in better analyzing and optimizing system performance.

/sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
        split
        split_failed
        split_deferred

This patch (of 2):

Currently, the split counters in THP statistics no longer include
PTE-mapped mTHP.  Therefore, we propose introducing per-order mTHP split
counters to monitor the frequency of mTHP splits.  This will help
developers better analyze and optimize system performance.

/sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
        split
        split_failed
        split_deferred

[ioworker0@gmail.com: make things more readable, per Barry and Baolin]
  Link: https://lkml.kernel.org/r/20240704012905.42971-2-ioworker0@gmail.com
[ioworker0@gmail.com: use == for `order' test, per David]
  Link: https://lkml.kernel.org/r/20240705113119.82210-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240704012905.42971-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240704012905.42971-2-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240628130750.73097-1-ioworker0@gmail.com
Link: https://lkml.kernel.org/r/20240628130750.73097-2-ioworker0@gmail.com


Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: Barry Song <baohua@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Bang Li <libang.li@antgroup.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit f216c845)
[lichunpeng@xiaomi.com: fixed merge conflicts in split_huge_page_to_list_to_order()]

Bug: 359422098
Change-Id: Idb9beff5577e77105c4c6ed36b552307c0f408f9
Signed-off-by: chunpeng li <lichunpeng@xiaomi.com>