[PATCH 03/19] writeback: reorganize [__]wb_update_bandwidth()

Tejun Heo
2015-05-22T22:29:48Z

__wb_update_bandwidth() is called from two places -
fs/fs-writeback.c::balance_dirty_pages() and
mm/page-writeback.c::wb_writeback(). The latter updates only the
write bandwidth while the former also deals with the dirty ratelimit.
The two callsites are distinguished by whether @thresh parameter is
zero or not, which is cryptic. In addition, the two files define
their own different versions of wb_update_bandwidth() on top of
__wb_update_bandwidth(), which is confusing to say the least. This
patch cleans up [__]wb_update_bandwidth() in the following ways.

* __wb_update_bandwidth() now takes explicit @update_ratelimit
parameter to gate dirty ratelimit handling.

* mm/page-writeback.c::wb_update_bandwidth() is flattened into its
caller - balance_dirty_pages().

* fs/fs-writeback.c::wb_update_bandwidth() is moved to
mm/page-writeback.c and __wb_update_bandwidth() is made static.

* While at it, add a lockdep assertion to __wb_update_bandwidth().

Except for the lockdep addition, this is pure reorganization and
doesn't introduce any behavioral changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
---
fs/fs-writeback.c | 10 ----------
include/linux/writeback.h | 9 +--------
mm/page-writeback.c | 45 ++++++++++++++++++++++-----------------------
3 files changed, 23 insertions(+), 41 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index b1b3b81..cd89484 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1088,16 +1088,6 @@ static bool over_bground_thresh(struct bdi_writeback *wb)
}

/*
- * Called under wb->list_lock. If there are multiple wb per bdi,
- * only the flusher working on the first wb should do it.
- */
-static void wb_update_bandwidth(struct bdi_writeback *wb,
- unsigned long start_time)
-{
- __wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time);
-}
-
-/*
* Explicit flushing or periodic writeback of "old" data.
*
* Define "old": the first time one of an inode's pages is dirtied, we mark the
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0435c85..80adf3d 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -157,14 +157,7 @@ int dirty_writeback_centisecs_handler(struct ctl_table *, int,
void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh);

-void __wb_update_bandwidth(struct bdi_writeback *wb,
- unsigned long thresh,
- unsigned long bg_thresh,
- unsigned long dirty,
- unsigned long bdi_thresh,
- unsigned long bdi_dirty,
- unsigned long start_time);
-
+void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time);
void page_writeback_init(void);
void balance_dirty_pages_ratelimited(struct address_space *mapping);

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c7745a7..bebdd41 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1160,19 +1160,22 @@ static void wb_update_dirty_ratelimit(struct bdi_writeback *wb,
trace_bdi_dirty_ratelimit(wb->bdi, dirty_rate, task_ratelimit);
}

-void __wb_update_bandwidth(struct bdi_writeback *wb,
- unsigned long thresh,
- unsigned long bg_thresh,
- unsigned long dirty,
- unsigned long wb_thresh,
- unsigned long wb_dirty,
- unsigned long start_time)
+static void __wb_update_bandwidth(struct bdi_writeback *wb,
+ unsigned long thresh,
+ unsigned long bg_thresh,
+ unsigned long dirty,
+ unsigned long wb_thresh,
+ unsigned long wb_dirty,
+ unsigned long start_time,
+ bool update_ratelimit)
{
unsigned long now = jiffies;
unsigned long elapsed = now - wb->bw_time_stamp;
unsigned long dirtied;
unsigned long written;

+ lockdep_assert_held(&wb->list_lock);
+
/*
* rate-limit, only update once every 200ms.
*/
@@ -1189,7 +1192,7 @@ void __wb_update_bandwidth(struct bdi_writeback *wb,
if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
goto snapshot;

- if (thresh) {
+ if (update_ratelimit) {
global_update_bandwidth(thresh, dirty, now);
wb_update_dirty_ratelimit(wb, thresh, bg_thresh, dirty,
wb_thresh, wb_dirty,
@@ -1203,20 +1206,9 @@ void __wb_update_bandwidth(struct bdi_writeback *wb,
wb->bw_time_stamp = now;
}

-static void wb_update_bandwidth(struct bdi_writeback *wb,
- unsigned long thresh,
- unsigned long bg_thresh,
- unsigned long dirty,
- unsigned long wb_thresh,
- unsigned long wb_dirty,
- unsigned long start_time)
+void wb_update_bandwidth(struct bdi_writeback *wb, unsigned long start_time)
{
- if (time_is_after_eq_jiffies(wb->bw_time_stamp + BANDWIDTH_INTERVAL))
- return;
- spin_lock(&wb->list_lock);
- __wb_update_bandwidth(wb, thresh, bg_thresh, dirty,
- wb_thresh, wb_dirty, start_time);
- spin_unlock(&wb->list_lock);
+ __wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time, false);
}

/*
@@ -1467,8 +1459,15 @@ static void balance_dirty_pages(struct address_space *mapping,
if (dirty_exceeded && !wb->dirty_exceeded)
wb->dirty_exceeded = 1;

- wb_update_bandwidth(wb, dirty_thresh, background_thresh,
- nr_dirty, wb_thresh, wb_dirty, start_time);
+ if (time_is_before_jiffies(wb->bw_time_stamp +
+ BANDWIDTH_INTERVAL)) {
+ spin_lock(&wb->list_lock);
+ __wb_update_bandwidth(wb, dirty_thresh,
+ background_thresh, nr_dirty,
+ wb_thresh, wb_dirty, start_time,
+ true);
+ spin_unlock(&wb->list_lock);
+ }

dirty_ratelimit = wb->dirty_ratelimit;
pos_ratio = wb_position_ratio(wb, dirty_thresh,
--
2.4.0