[PATCH 11/45] writeback, blkcg: propagate non-root blkcg congestion state

[Tejun Heo]

Now that bdi layer can handle per cgwb (cgroup bdi_writeback)
congestion state, blk_{set|clear}_congested() can propagate non-root
blkcg congestion state to them.

This can be easily achieved by disabling the root_rl tests in
blk_{set|clear}_congested().  Note that we still need those tests when
!CONFIG_CGROUP_WRITEBACK as otherwise we'll end up flipping root blkcg
wb's congestion state for events happening on other blkcgs.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
 block/blk-core.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index c9a7d6c..d731f1a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -65,23 +65,26 @@ static struct workqueue_struct *kblockd_workqueue;
 
 static void blk_clear_congested(struct request_list *rl, int sync)
 {
-	if (rl != &rl->q->root_rl)
-		return;
 #ifdef CONFIG_CGROUP_WRITEBACK
 	clear_wb_congested(rl->blkg->wb, sync);
 #else
-	clear_wb_congested(&rl->q->backing_dev_info.wb, sync);
+	/*
+	 * If !CGROUP_WRITEBACK, all blkg's map to bdi->wb and we shouldn't
+	 * flip its congestion state for events on other blkcgs.
+	 */
+	if (rl == &rl->q->root_rl)
+		clear_wb_congested(&rl->q->backing_dev_info.wb, sync);
 #endif
 }
 
 static void blk_set_congested(struct request_list *rl, int sync)
 {
-	if (rl != &rl->q->root_rl)
-		return;
 #ifdef CONFIG_CGROUP_WRITEBACK
 	set_wb_congested(rl->blkg->wb, sync);
 #else
-	set_wb_congested(&rl->q->backing_dev_info.wb, sync);
+	/* see blk_clear_congested() */
+	if (rl == &rl->q->root_rl)
+		set_wb_congested(&rl->q->backing_dev_info.wb, sync);
 #endif
 }
 
-- 
2.1.0

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