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Message-ID: <20240409192301.907377-7-david@redhat.com>
Date: Tue, 9 Apr 2024 21:22:49 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
linux-doc@...r.kernel.org,
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David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
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Richard Chang <richardycc@...gle.com>
Subject: [PATCH v1 06/18] mm: make folio_mapcount() return 0 for small typed folios
We already handle it properly for large folios. Let's also return "0"
for small typed folios, like page_mapcount() currently would.
Consequently, folio_mapcount() will never return negative values for
typed folios, but may return negative values for underflows.
Signed-off-by: David Hildenbrand <david@...hat.com>
---
include/linux/mm.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index daf687f0e8e5..d453232bba62 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1260,12 +1260,19 @@ static inline int folio_large_mapcount(const struct folio *folio)
* references the entire folio counts exactly once, even when such special
* page table entries are comprised of multiple ordinary page table entries.
*
+ * Will report 0 for pages which cannot be mapped into userspace, such as
+ * slab, page tables and similar.
+ *
* Return: The number of times this folio is mapped.
*/
static inline int folio_mapcount(const struct folio *folio)
{
- if (likely(!folio_test_large(folio)))
- return atomic_read(&folio->_mapcount) + 1;
+ int mapcount;
+
+ if (likely(!folio_test_large(folio))) {
+ mapcount = atomic_read(&folio->_mapcount);
+ return page_type_has_type(mapcount) ? 0 : mapcount + 1;
+ }
return folio_large_mapcount(folio);
}
--
2.44.0
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