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Subject[PATCH 18/18] writeback: rearrange the wb_writeback() loop
Move the terminate conditions to the end of the loop, and move the
work->older_than_this updates close to each others.

Proposed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/fs-writeback.c | 58 +++++++++++++++++++++++---------------------
1 file changed, 31 insertions(+), 27 deletions(-)

--- linux-next.orig/fs/fs-writeback.c 2011-05-20 05:41:35.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-20 05:41:36.000000000 +0800
@@ -712,42 +712,22 @@ static long wb_writeback(struct bdi_writ
unsigned long oldest_jif;
struct inode *inode;
long progress;
+ bool bg_retry_all = false;

oldest_jif = jiffies;
work->older_than_this = &oldest_jif;

spin_lock(&wb->list_lock);
for (;;) {
- /*
- * Stop writeback when nr_pages has been consumed
- */
- if (work->nr_pages <= 0)
- break;
-
- /*
- * Background writeout and kupdate-style writeback may
- * run forever. Stop them if there is other work to do
- * so that e.g. sync can proceed. They'll be restarted
- * after the other works are all done.
- */
- if ((work->for_background || work->for_kupdate) &&
- !list_empty(&wb->bdi->work_list))
- break;
-
- /*
- * For background writeout, stop when we are below the
- * background dirty threshold
- */
- if (work->for_background && !over_bground_thresh())
- break;
-
- if (work->for_kupdate || work->for_background) {
+ if (bg_retry_all) {
+ bg_retry_all = false;
+ work->older_than_this = NULL;
+ } else if (work->for_kupdate || work->for_background) {
oldest_jif = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
work->older_than_this = &oldest_jif;
}

-retry:
trace_writeback_start(wb->bdi, work);
if (list_empty(&wb->b_io))
queue_io(wb, work->older_than_this);
@@ -777,14 +757,38 @@ retry:
work->older_than_this &&
list_empty(&wb->b_io) &&
list_empty(&wb->b_more_io)) {
- work->older_than_this = NULL;
- goto retry;
+ bg_retry_all = true;
+ continue;
}
/*
* No more inodes for IO, bail
*/
if (list_empty(&wb->b_more_io))
break;
+
+ /*
+ * Stop writeback when nr_pages has been consumed
+ */
+ if (work->nr_pages <= 0)
+ break;
+
+ /*
+ * For background writeout, stop when we are below the
+ * background dirty threshold
+ */
+ if (work->for_background && !over_bground_thresh())
+ break;
+
+ /*
+ * Background writeout and kupdate-style writeback may
+ * run forever. Stop them if there is other work to do
+ * so that e.g. sync can proceed. They'll be restarted
+ * after the other works are all done.
+ */
+ if ((work->for_background || work->for_kupdate) &&
+ !list_empty(&wb->bdi->work_list))
+ break;
+
/*
* Nothing written. Wait for some inode to
* become available for writeback. Otherwise



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