linux-kernel - [PATCH v1] mm/rmap: cleanup partially-mapped handling in __folio_remove

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Date: Tue, 18 Jun 2024 17:10:26 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	Yosry Ahmed <yosryahmed@...gle.com>
Subject: [PATCH v1] 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.

Cc: Yosry Ahmed <yosryahmed@...gle.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/rmap.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index afec4b6800caf..aa900e46cdf82 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1551,11 +1551,12 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
 			}
 		}
 
-		partially_mapped = nr < nr_pmdmapped;
+		partially_mapped = nr && nr < nr_pmdmapped;
 		break;
 	}
 
-	if (nr) {
+	if (partially_mapped && folio_test_anon(folio) &&
+	    list_empty(&folio->_deferred_list))
 		/*
 		 * Queue anon large folio for deferred split if at least one
 		 * page of the folio is unmapped and at least one page
@@ -1563,10 +1564,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
 		 *
 		 * 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);
-	}
+		deferred_split_folio(folio);
 	__folio_mod_stat(folio, -nr, -nr_pmdmapped);
 
 	/*
-- 
2.45.2