[PATCH 31/45] writeback: sync old inodes first in background writeback

[Wu Fengguang]

A background flush work may run for ever. So it's reasonable for it to
mimic the kupdate behavior of syncing old/expired inodes first.

CC: Jan Kara <jack@xxxxxxx> 
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/fs-writeback.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

--- linux.orig/fs/fs-writeback.c	2009-10-06 23:39:28.000000000 +0800
+++ linux/fs/fs-writeback.c	2009-10-06 23:39:31.000000000 +0800
@@ -680,7 +680,7 @@ static long writeback_inodes_wb(struct b
 
 	spin_lock(&inode_lock);
 
-	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+	if (list_empty(&wb->b_io))
 		queue_io(wb, wbc->older_than_this);
 
 	while (!list_empty(&wb->b_io)) {
@@ -793,14 +793,15 @@ static long wb_writeback(struct bdi_writ
 		.range_cyclic		= args->range_cyclic,
 	};
 	unsigned long oldest_jif;
+	int expire_interval = msecs_to_jiffies(dirty_expire_interval * 10);
+	int fg_rounds = 0;
 	long wrote = 0;
 	long nr;
 	struct inode *inode;
 
-	if (wbc.for_kupdate) {
+	if (wbc.for_kupdate || wbc.for_background) {
 		wbc.older_than_this = &oldest_jif;
-		oldest_jif = jiffies -
-				msecs_to_jiffies(dirty_expire_interval * 10);
+		oldest_jif = jiffies - expire_interval;
 	}
 	if (!wbc.range_cyclic) {
 		wbc.range_start = 0;
@@ -828,6 +829,18 @@ static long wb_writeback(struct bdi_writ
 		args->nr_pages -= nr;
 		wrote += nr;
 
+		if (args->for_background && expire_interval &&
+		    ++fg_rounds && list_empty(&wb->b_io)) {
+			if (fg_rounds < 10)
+				expire_interval >>= 1;
+			if (expire_interval)
+				oldest_jif = jiffies - expire_interval;
+			else
+				wbc.older_than_this = 0;
+			fg_rounds = 0;
+			continue;
+		}
+
 		/*
 		 * Bail if no more IO
 		 */


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