linux-kernel - [RFC] mm: use folio_expected_ref_count() helper for reference counting

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Message-ID: <20250609170806.447302-2-shivankg@amd.com>
Date: Mon, 9 Jun 2025 17:08:07 +0000
From: Shivank Garg <shivankg@....com>
To: <mhiramat@...nel.org>, <oleg@...hat.com>, <peterz@...radead.org>,
	<mingo@...hat.com>, <acme@...nel.org>, <namhyung@...nel.org>,
	<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
	<jolsa@...nel.org>, <irogers@...gle.com>, <adrian.hunter@...el.com>,
	<kan.liang@...ux.intel.com>, <david@...hat.com>, <akpm@...ux-foundation.org>
CC: <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
	<linux-perf-users@...r.kernel.org>, <linux-mm@...ck.org>, Shivank Garg
	<shivankg@....com>
Subject: [RFC] mm: use folio_expected_ref_count() helper for reference counting

Replace open-coded folio reference count calculations with the
folio_expected_ref_count() helper to improve code maintainability
and reduce duplication.

No functional changes intended.

Signed-off-by: Shivank Garg <shivankg@....com>
---
 kernel/events/uprobes.c | 5 +++--
 mm/memfd.c              | 4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4c965ba77f9f..c978c8c27340 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -434,10 +434,11 @@ static int __uprobe_write_opcode(struct vm_area_struct *vma,
 	/*
 	 * When unregistering, we may only zap a PTE if uffd is disabled and
 	 * there are no unexpected folio references ...
+	 * Expected refs: mappings + swapcache.
+	 * We hold one additional reference (+1).
 	 */
 	if (is_register || userfaultfd_missing(vma) ||
-	    (folio_ref_count(folio) != folio_mapcount(folio) + 1 +
-	     folio_test_swapcache(folio) * folio_nr_pages(folio)))
+	    (folio_ref_count(folio) != folio_expected_ref_count(folio) + 1))
 		goto remap;
 
 	/*
diff --git a/mm/memfd.c b/mm/memfd.c
index ab367e61553d..4ed5506221b7 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -32,8 +32,8 @@
 
 static bool memfd_folio_has_extra_refs(struct folio *folio)
 {
-	return folio_ref_count(folio) - folio_mapcount(folio) !=
-	       folio_nr_pages(folio);
+	/* Expected refs: pagecache + mappings */
+	return folio_ref_count(folio) != folio_expected_ref_count(folio);
 }
 
 static void memfd_tag_pins(struct xa_state *xas)
-- 
2.43.0