mm/huge_memory: improve split_huge_page_to_list_to_order() return value documentation

The documentation is wrong and relying on it almost resulted in BUGs in
new callers: ever since fd4a7ac32918 ("mm: migrate: try again if THP split
is failed due to page refcnt") we return -EAGAIN on unexpected folio
references, not -EBUSY.

Let's fix that and also document which other return values we can
currently see and why they could happen.

[[email protected]: v2]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions