writeback: fix WB_SYNC_NONE writeback from umount

When umount calls sync_filesystem(), we first do a WB_SYNC_NONE
writeback to kick off writeback of pending dirty inodes, then follow
that up with a WB_SYNC_ALL to wait for it. Since umount already holds
the sb s_umount mutex, WB_SYNC_NONE ends up doing nothing and all
writeback happens as WB_SYNC_ALL. This can greatly slow down umount,
since WB_SYNC_ALL writeback is a data integrity operation and thus
a bigger hammer than simple WB_SYNC_NONE. For barrier aware file systems
it's a lot slower.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d0f2b3765f8d..53b2fcf2d283 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -597,7 +597,7 @@ static void balance_dirty_pages(struct address_space *mapping,
             (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
                                + global_page_state(NR_UNSTABLE_NFS))
                                           > background_thresh)))
-                bdi_start_writeback(bdi, NULL, 0);
+                bdi_start_writeback(bdi, NULL, 0, 0);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -705,7 +705,7 @@ void laptop_mode_timer_fn(unsigned long data)
          */
 
         if (bdi_has_dirty_io(&q->backing_dev_info))
-                bdi_start_writeback(&q->backing_dev_info, NULL, nr_pages);
+                bdi_start_writeback(&q->backing_dev_info, NULL, 0, nr_pages);
 }
 
 /*