mm/compaction: add support for >0 order folio memory compaction.

Before last commit, memory compaction only migrates order-0 folios and
skips >0 order folios.  Last commit splits all >0 order folios during
compaction.  This commit migrates >0 order folios during compaction by
keeping isolated free pages at their original size without splitting them
into order-0 pages and using them directly during migration process.

What is different from the prior implementation:
1. All isolated free pages are kept in a NR_PAGE_ORDERS array of page
   lists, where each page list stores free pages in the same order.
2. All free pages are not post_alloc_hook() processed nor buddy pages,
   although their orders are stored in first page's private like buddy
   pages.
3. During migration, in new page allocation time (i.e., in
   compaction_alloc()), free pages are then processed by post_alloc_hook().
   When migration fails and a new page is returned (i.e., in
   compaction_free()), free pages are restored by reversing the
   post_alloc_hook() operations using newly added
   free_pages_prepare_fpi_none().

Step 3 is done for a latter optimization that splitting and/or merging
free pages during compaction becomes easier.

Note: without splitting free pages, compaction can end prematurely due to
migration will return -ENOMEM even if there is free pages.  This happens
when no order-0 free page exist and compaction_alloc() return NULL.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Zi Yan <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Tested-by: Baolin Wang <[email protected]>
Tested-by: Yu Zhao <[email protected]>
Cc: Adam Manzanares <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Luis Chamberlain <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yin Fengwei <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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