Btrfs: only flush down bios for writeback pages

The btrfs write_cache_pages call has a flush function so that it submits
the bio it has been building before it waits on any writeback pages.

This adds a check so that flush only happens on writeback pages.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 3a65c10dce33..87dba8517935 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2462,7 +2462,8 @@ retry:
                         }
 
                         if (wbc->sync_mode != WB_SYNC_NONE) {
-                                flush_fn(data);
+                                if (PageWriteback(page))
+                                        flush_fn(data);
                                 wait_on_page_writeback(page);
                         }