2 files changed, 5 insertions, 2 deletions

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index a398ecdbd758..1f528fad3516 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -788,10 +788,11 @@ static const struct file_operations zero_fops = {
 /*
  * capabilities for /dev/zero
  * - permits private mappings, "copies" are taken of the source of zeros
+ * - no writeback happens
  */
 static struct backing_dev_info zero_bdi = {
         .name           = "char/mem",
-        .capabilities   = BDI_CAP_MAP_COPY,
+        .capabilities   = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static const struct file_operations full_fops = {
diff --git a/fs/char_dev.c b/fs/char_dev.c
index f80a4f25123c..143d393881cb 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -40,7 +40,9 @@ struct backing_dev_info directly_mappable_cdev_bdi = {
 #endif
                 /* permit direct mmap, for read, write or exec */
                 BDI_CAP_MAP_DIRECT |
-                BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
+                BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP |
+                /* no writeback happens */
+                BDI_CAP_NO_ACCT_AND_WRITEBACK),
 };
 
 static struct kobj_map *cdev_map;