mm/huge_memory: add buddy allocator like (non-uniform) folio_split()

mm/huge_memory: add buddy allocator like (non-uniform) folio_split()

folio_split() splits a large folio in the same way as buddy allocator
splits a large free page for allocation.  The purpose is to minimize the
number of folios after the split.  For example, if user wants to free the
3rd subpage in a order-9 folio, folio_split() will split the order-9 folio
as:

O-0, O-0, O-0, O-0, O-2, O-3, O-4, O-5, O-6, O-7, O-8 if it is anon,
since anon folio does not support order-1 yet.
-----------------------------------------------------------------
|   |   |   |   |     |   |       |                             |
|O-0|O-0|O-0|O-0| O-2 |...|  O-7  |             O-8             |
|   |   |   |   |     |   |       |                             |
-----------------------------------------------------------------

O-1,      O-0, O-0, O-2, O-3, O-4, O-5, O-6, O-7, O-9 if it is pagecache
---------------------------------------------------------------
|     |   |   |     |   |       |                             |
| O-1 |O-0|O-0| O-2 |...|  O-7  |             O-8             |
|     |   |   |     |   |       |                             |
---------------------------------------------------------------

It generates fewer folios (i.e., 11 or 10) than existing page split
approach, which splits the order-9 to 512 order-0 folios.  It also reduces
the number of new xa_node needed during a pagecache folio split from 8 to
1, potentially decreasing the folio split failure rate due to memory
constraints.

folio_split() and existing split_huge_page_to_list_to_order() share the
folio unmapping and remapping code in __folio_split() and the common
backend split code in __split_unmapped_folio() using uniform_split
variable to distinguish their operations.

uniform_split_supported() and non_uniform_split_supported() are added to
factor out check code and will be used outside __folio_split() in the
following commit.

Link: https://lkml.kernel.org/r/20250226210032.2044041-5-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>