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authorTejun Heo <tj@kernel.org>2015-05-22 17:13:47 -0400
committerJens Axboe <axboe@fb.com>2015-06-02 08:33:36 -0600
commit95a46c65e3c09edb9f17dabf2dc16670cd328739 (patch)
tree2ff8187223f5f5671394dd9ee84719f3ff934a14 /mm/page-writeback.c
parent766a9d6e60578f1ef6de71f89f022084f8bffc82 (diff)
writeback: make bdi_has_dirty_io() take multiple bdi_writeback's into account
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>
Diffstat (limited to 'mm/page-writeback.c')
-rw-r--r--mm/page-writeback.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c95eb24dd652..99b88465096e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -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;
}