each queue will have a state machine. Initially queue is in LIMIT_HIGH
state, which means all cgroups will be throttled according to their high
limit. After all cgroups with high limit cross the limit, the queue state
gets upgraded to LIMIT_MAX state.
cgroups without high limit will use max limit for their high limit.

Signed-off-by: Shaohua Li <s...@fb.com>
---
 block/blk-throttle.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index a564215..ec53671 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -208,12 +208,29 @@ static struct throtl_data *sq_to_td(struct 
throtl_service_queue *sq)
 
 static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
 {
-       return tg->bps[rw][tg->td->limit_index];
+       struct blkcg_gq *blkg = tg_to_blkg(tg);
+       uint64_t ret;
+
+       if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
+               return -1;
+       ret = tg->bps[rw][tg->td->limit_index];
+       if (ret == -1 && tg->td->limit_index == LIMIT_HIGH)
+               return tg->bps[rw][LIMIT_MAX];
+
+       return ret;
 }
 
 static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
 {
-       return tg->iops[rw][tg->td->limit_index];
+       struct blkcg_gq *blkg = tg_to_blkg(tg);
+       unsigned int ret;
+
+       if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
+               return -1;
+       ret = tg->iops[rw][tg->td->limit_index];
+       if (ret == -1 && tg->td->limit_index == LIMIT_HIGH)
+               return tg->iops[rw][LIMIT_MAX];
+       return ret;
 }
 
 /**
-- 
2.9.3

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