[PATCH 5.10/5.15 v2 1/1 RFC] mm/truncate: Replace page_mapped() call in invalidate_inode_page()

[Roman Smirnov]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

commit e41c81d0d30e1a6ebf408feaf561f80cac4457dc upstream.

folio_mapped() is expensive because it has to check each page's mapcount
field.  A cheaper check is whether there are any extra references to
the page, other than the one we own, one from the page private data and
the ones held by the page cache.

The call to remove_mapping() will fail in any case if it cannot freeze
the refcount, but failing here avoids cycling the i_pages spinlock.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
[Roman: replaced folio_ref_count() call with page_ref_count(),
folio_nr_pages() call with compound_nr(), and
folio_has_private() call with page_has_private()]
Signed-off-by: Roman Smirnov <r.smirnov@xxxxxx>
---
 mm/truncate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/truncate.c b/mm/truncate.c
index 8914ca4ce4b1..989bc7785d55 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -256,7 +256,9 @@ int invalidate_inode_page(struct page *page)
 		return 0;
 	if (PageDirty(page) || PageWriteback(page))
 		return 0;
-	if (page_mapped(page))
+	/* The refcount will be elevated if the page is used by the system */
+	if (page_ref_count(page) >
+			compound_nr(page) + page_has_private(page) + 1)
 		return 0;
 	return invalidate_complete_page(mapping, page);
 }
-- 
2.34.1