Let's get rid of the compound parameter and instead define explicitly
which mappings we're adding.  That is more future proof, easier to read
and harder to mess up.

Use an enum to express the granularity internally.  Make the compiler
always special-case on the granularity by using __always_inline.  Replace
the "compound" check by a switch-case that will be removed by the compiler
completely.

Add plenty of sanity checks with CONFIG_DEBUG_VM.  Replace the
folio_test_pmd_mappable() check by a config check in the caller and sanity
checks.  Convert the single user of folio_add_file_rmap_range().

While at it, consistently use "int" instead of "unisgned int" in rmap code
when dealing with mapcounts and the number of pages.

This function design can later easily be extended to PUDs and to batch
PMDs.  Note that for now we don't support anything bigger than PMD-sized
folios (as we cleanly separated hugetlb handling).  Sanity checks will
catch if that ever changes.

Next up is removing page_remove_rmap() along with its "compound" parameter
and smilarly converting all other rmap functions.

Link: https://lkml.kernel.org/r/20231220224504.646757-8-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>