mm/rmap: cleanup partially-mapped handling in __folio_remove_rmap()

Let's simplify and reduce code indentation.  In the RMAP_LEVEL_PTE case,
we already check for nr when computing partially_mapped.

For RMAP_LEVEL_PMD, it's a bit more confusing.  Likely, we don't need the
"nr" check, but we could have "nr < nr_pmdmapped" also if we stumbled into
the "/* Raced ahead of another remove and an add?  */" case.  So let's
simply move the nr check in there.

Note that partially_mapped is always false for small folios.

No functional change intended.

Link: https://lkml.kernel.org/r/20240710214350.147864-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index 2630bde38640c23a168ee521622d8e80c0c229af..9019502009573f01708ab9b3936714b023432123 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1568,22 +1568,19 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
                        }
                }
 
-               partially_mapped = nr < nr_pmdmapped;
+               partially_mapped = nr && nr < nr_pmdmapped;
                break;
        }
 
-       if (nr) {
-               /*
-                * Queue anon large folio for deferred split if at least one
-                * page of the folio is unmapped and at least one page
-                * is still mapped.
-                *
-                * Check partially_mapped first to ensure it is a large folio.
-                */
-               if (folio_test_anon(folio) && partially_mapped &&
-                   list_empty(&folio->_deferred_list))
-                       deferred_split_folio(folio);
-       }
+       /*
+        * Queue anon large folio for deferred split if at least one page of
+        * the folio is unmapped and at least one page is still mapped.
+        *
+        * Check partially_mapped first to ensure it is a large folio.
+        */
+       if (partially_mapped && folio_test_anon(folio) &&
+           list_empty(&folio->_deferred_list))
+               deferred_split_folio(folio);
        __folio_mod_stat(folio, -nr, -nr_pmdmapped);
 
        /*