@@ -87,6 +87,7 @@ static bool wb_io_lists_populated(struct bdi_writeback *wb)
return false;
} else {
set_bit(WB_has_dirty_io, &wb->state);
+ WARN_ON_ONCE(!wb->avg_write_bandwidth);
atomic_long_add(wb->avg_write_bandwidth,
&wb->bdi->tot_write_bandwidth);
return true;
@@ -98,8 +99,8 @@ static void wb_io_lists_depopulated(struct bdi_writeback *wb)
if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
clear_bit(WB_has_dirty_io, &wb->state);
- atomic_long_sub(wb->avg_write_bandwidth,
- &wb->bdi->tot_write_bandwidth);
+ WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
+ &wb->bdi->tot_write_bandwidth) < 0);
}
}
@@ -98,7 +98,7 @@ struct bdi_writeback {
unsigned long dirtied_stamp;
unsigned long written_stamp; /* pages written at bw_time_stamp */
unsigned long write_bandwidth; /* the estimated write bandwidth */
- unsigned long avg_write_bandwidth; /* further smoothed write bw */
+ unsigned long avg_write_bandwidth; /* further smoothed write bw, > 0 */
/*
* The base dirty throttle rate, re-calculated on every 200ms.
@@ -142,7 +142,11 @@ struct backing_dev_info {
unsigned int min_ratio;
unsigned int max_ratio, max_prop_frac;
- atomic_long_t tot_write_bandwidth; /* sum of active avg_write_bw */
+ /*
+ * Sum of avg_write_bw of wbs with dirty inodes. > 0 if there are
+ * any dirty wbs, which is depended upon by bdi_has_dirty().
+ */
+ atomic_long_t tot_write_bandwidth;
struct bdi_writeback wb; /* the root writeback info for this bdi */
struct bdi_writeback_congested wb_congested; /* its congested state */
@@ -29,7 +29,6 @@ void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
enum wb_reason reason);
void bdi_start_background_writeback(struct backing_dev_info *bdi);
void wb_workfn(struct work_struct *work);
-bool bdi_has_dirty_io(struct backing_dev_info *bdi);
void wb_wakeup_delayed(struct bdi_writeback *wb);
extern spinlock_t bdi_lock;
@@ -42,6 +41,15 @@ static inline bool wb_has_dirty_io(struct bdi_writeback *wb)
return test_bit(WB_has_dirty_io, &wb->state);
}
+static inline bool bdi_has_dirty_io(struct backing_dev_info *bdi)
+{
+ /*
+ * @bdi->tot_write_bandwidth is guaranteed to be > 0 if there are
+ * any dirty wbs. See wb_update_write_bandwidth().
+ */
+ return atomic_long_read(&bdi->tot_write_bandwidth);
+}
+
static inline void __add_wb_stat(struct bdi_writeback *wb,
enum wb_stat_item item, s64 amount)
{
@@ -256,11 +256,6 @@ static int __init default_bdi_init(void)
}
subsys_initcall(default_bdi_init);
-bool bdi_has_dirty_io(struct backing_dev_info *bdi)
-{
- return wb_has_dirty_io(&bdi->wb);
-}
-
/*
* This function is used when the first inode for this wb is marked dirty. It
* wakes-up the corresponding bdi thread which should then take care of the
@@ -881,9 +881,13 @@ static void wb_update_write_bandwidth(struct bdi_writeback *wb,
avg += (old - avg) >> 3;
out:
- if (wb_has_dirty_io(wb))
- atomic_long_add(avg - wb->avg_write_bandwidth,
- &wb->bdi->tot_write_bandwidth);
+ /* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
+ avg = max(avg, 1LU);
+ if (wb_has_dirty_io(wb)) {
+ long delta = avg - wb->avg_write_bandwidth;
+ WARN_ON_ONCE(atomic_long_add_return(delta,
+ &wb->bdi->tot_write_bandwidth) <= 0);
+ }
wb->write_bandwidth = bw;
wb->avg_write_bandwidth = avg;
}
bdi_has_dirty_io() used to only reflect whether the root wb (bdi_writeback) has dirty inodes. For cgroup writeback support, it needs to take all active wb's into account. If any wb on the bdi has dirty inodes, bdi_has_dirty_io() should return true. To achieve that, as inode_wb_list_{move|del}_locked() now keep track of the dirty state transition of each wb, the number of dirty wbs can be counted in the bdi; however, bdi is already aggregating wb->avg_write_bandwidth which can easily be guaranteed to be > 0 when there are any dirty inodes by ensuring wb->avg_write_bandwidth can't dip below 1. bdi_has_dirty_io() can simply test whether bdi->tot_write_bandwidth is zero or not. While this bumps the value of wb->avg_write_bandwidth to one when it used to be zero, this shouldn't cause any meaningful behavior difference. bdi_has_dirty_io() is made an inline function which tests whether ->tot_write_bandwidth is non-zero. Also, WARN_ON_ONCE()'s on its value are added to inode_wb_list_{move|del}_locked(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> --- fs/fs-writeback.c | 5 +++-- include/linux/backing-dev-defs.h | 8 ++++++-- include/linux/backing-dev.h | 10 +++++++++- mm/backing-dev.c | 5 ----- mm/page-writeback.c | 10 +++++++--- 5 files changed, 25 insertions(+), 13 deletions(-)