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writeback: make bdi_has_dirty_io() take multiple bdi_writeback's into account

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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>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-05-22 17:13:47 -04:00 • committed by Jens Axboe
parent 766a9d6e60
commit 95a46c65e3
5 changed files with 25 additions and 13 deletions
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8
include/linux/backing-dev-defs.h
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@ -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 */