writeback: introduce writeback_control.inodes_written

The flusher works on dirty inodes in batches, and may quit prematurely
if the batch of inodes happen to be metadata-only dirtied: in this case
wbc->nr_to_write won't be decreased at all, which stands for "no pages
written" but also mis-interpreted as "no progress".

So introduce writeback_control.inodes_written to count the inodes get
cleaned from VFS POV.  A non-zero value means there are some progress on
writeback, in which case more writeback can be tried.

Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index fe190a8b0bc8..e4504299f4a5 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -464,6 +464,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                          * No need to add it back to the LRU.
                          */
                         list_del_init(&inode->i_wb_list);
+                        wbc->inodes_written++;
                 }
         }
         inode_sync_complete(inode);
@@ -725,6 +726,7 @@ static long wb_writeback(struct bdi_writeback *wb,
                 wbc.more_io = 0;
                 wbc.nr_to_write = write_chunk;
                 wbc.pages_skipped = 0;
+                wbc.inodes_written = 0;
 
                 trace_wbc_writeback_start(&wbc, wb->bdi);
                 if (work->sb)
@@ -741,6 +743,8 @@ static long wb_writeback(struct bdi_writeback *wb,
                  */
                 if (wbc.nr_to_write <= 0)
                         continue;
+                if (wbc.inodes_written)
+                        continue;
                 /*
                  * Didn't write everything and we don't have more IO, bail
                  */