writeback: separate starting of sync vs opportunistic writeback

bdi_start_writeback() is currently split into two paths, one for
WB_SYNC_NONE and one for WB_SYNC_ALL. Add bdi_sync_writeback()
for WB_SYNC_ALL writeback and let bdi_start_writeback() handle
only WB_SYNC_NONE.

Push down the writeback_control allocation and only accept the
parameters that make sense for each function. This cleans up
the API considerably.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 2 insertions, 10 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 12c3d843ce93..1eea4fa0d410 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -582,16 +582,8 @@ static void balance_dirty_pages(struct address_space *mapping)
         if ((laptop_mode && pages_written) ||
             (!laptop_mode && ((nr_writeback = global_page_state(NR_FILE_DIRTY)
                                           + global_page_state(NR_UNSTABLE_NFS))
-                                          > background_thresh))) {
-                struct writeback_control wbc = {
-                        .bdi            = bdi,
-                        .sync_mode      = WB_SYNC_NONE,
-                        .nr_to_write    = nr_writeback,
-                };
-
-
-                bdi_start_writeback(&wbc);
-        }
+                                          > background_thresh)))
+                bdi_start_writeback(bdi, nr_writeback);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)