writeback: avoid extra sync work at enqueue time

This removes writeback_control.wb_start and does more straightforward
sync livelock prevention by setting .older_than_this to prevent extra
inodes from being enqueued in the first place.

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

2 files changed, 3 insertions, 16 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 565b1fd15be6..d0553f33fb50 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -544,15 +544,6 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                         continue;
                 }
 
-                /*
-                 * Was this inode dirtied after sync_sb_inodes was called?
-                 * This keeps sync from extra jobs and livelock.
-                 */
-                if (inode_dirtied_after(inode, wbc->wb_start)) {
-                        spin_unlock(&inode->i_lock);
-                        return 1;
-                }
-
                 __iget(inode);
 
                 pages_skipped = wbc->pages_skipped;
@@ -585,9 +576,6 @@ static void __writeback_inodes_wb(struct bdi_writeback *wb,
 {
         int ret = 0;
 
-        if (!wbc->wb_start)
-                wbc->wb_start = jiffies; /* livelock avoidance */
-
         while (!list_empty(&wb->b_io)) {
                 struct inode *inode = wb_inode(wb->b_io.prev);
                 struct super_block *sb = inode->i_sb;
@@ -686,7 +674,9 @@ static long wb_writeback(struct bdi_writeback *wb,
         if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_writepages)
                 write_chunk = LONG_MAX;
 
-        wbc.wb_start = jiffies; /* livelock avoidance */
+        oldest_jif = jiffies;
+        wbc.older_than_this = &oldest_jif;
+
         spin_lock(&wb->list_lock);
         for (;;) {
                 /*
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index c2d957fb38d3..d8e96a480850 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -26,9 +26,6 @@ struct writeback_control {
         enum writeback_sync_modes sync_mode;
         unsigned long *older_than_this; /* If !NULL, only write back inodes
                                            older than this */
-        unsigned long wb_start;         /* Time writeback_inodes_wb was
-                                           called. This is needed to avoid
-                                           extra jobs and livelock */
         long nr_to_write;               /* Write this many pages, and decrement
                                            this for each page written */
         long pages_skipped;             /* Pages which were not written */