[PATCH 1/2] mm: add a mapping_clear_large_folios helper

[Christoph Hellwig <hch@lst.de>]

Users of shmem_kernel_file_setup might not be able to deal with large
folios (yet).  Give them a way to disable large folio support on their
mapping.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/pagemap.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 06142ff7f9ce0e..352d1f8423292c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -343,6 +343,20 @@ static inline void mapping_set_large_folios(struct address_space *mapping)
 	__set_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
 }
 
+/**
+ * mapping_clear_large_folios() - Disable large folio support for a mapping
+ * @mapping: The mapping.
+ *
+ * This can be called to undo the effect of mapping_set_large_folios().
+ *
+ * Context: This should not be called while the inode is active as it
+ * is non-atomic.
+ */
+static inline void mapping_clear_large_folios(struct address_space *mapping)
+{
+	__clear_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
+}
+
 /*
  * Large folio support currently depends on THP.  These dependencies are
  * being worked on but are not yet fixed.
-- 
2.39.2