[PATCH v4 1/6] mm: add AS_WRITEBACK_MAY_BLOCK mapping flag

[Joanne Koong <joannelkoong@gmail.com>]

Add a new mapping flag AS_WRITEBACK_MAY_BLOCK which filesystems may set
to indicate that writeback operations may block or take an indeterminate
amount of time to complete. Extra caution should be taken when waiting
on writeback for folios belonging to mappings where this flag is set.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/pagemap.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 68a5f1ff3301..eb5a7837e142 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -210,6 +210,7 @@ enum mapping_flags {
 	AS_STABLE_WRITES = 7,	/* must wait for writeback before modifying
 				   folio contents */
 	AS_INACCESSIBLE = 8,	/* Do not attempt direct R/W access to the mapping */
+	AS_WRITEBACK_MAY_BLOCK = 9, /* Use caution when waiting on writeback */
 	/* Bits 16-25 are used for FOLIO_ORDER */
 	AS_FOLIO_ORDER_BITS = 5,
 	AS_FOLIO_ORDER_MIN = 16,
@@ -335,6 +336,16 @@ static inline bool mapping_inaccessible(struct address_space *mapping)
 	return test_bit(AS_INACCESSIBLE, &mapping->flags);
 }
 
+static inline void mapping_set_writeback_may_block(struct address_space *mapping)
+{
+	set_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
+}
+
+static inline bool mapping_writeback_may_block(struct address_space *mapping)
+{
+	return test_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
 	return mapping->gfp_mask;
-- 
2.43.5