writeback: Include all dirty inodes in background writeback

Current livelock avoidance code makes background work to include only inodes
that were dirtied before background writeback has started. However background
writeback can be running for a long time and thus excluding newly dirtied
inodes can eventually exclude significant portion of dirty inodes making
background writeback inefficient. Since background writeback avoids livelocking
the flusher thread by yielding to any other work, there is no real reason why
background work should not include all dirty inodes so change the logic in
wb_writeback().

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 517f211a3bd45c60f607e5da7d957bc739d55d47..92d353e069dc471092cc396b8c74ce874c5f19f8 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -743,11 +743,17 @@ static long wb_writeback(struct bdi_writeback *wb,
                if (work->for_background && !over_bground_thresh(wb->bdi))
                        break;
 
+               /*
+                * Kupdate and background works are special and we want to
+                * include all inodes that need writing. Livelock avoidance is
+                * handled by these works yielding to any other work so we are
+                * safe.
+                */
                if (work->for_kupdate) {
                        oldest_jif = jiffies -
                                msecs_to_jiffies(dirty_expire_interval * 10);
-                       work->older_than_this = &oldest_jif;
-               }
+               } else if (work->for_background)
+                       oldest_jif = jiffies;
 
                trace_writeback_start(wb->bdi, work);
                if (list_empty(&wb->b_io))