Re: [RFC PATCH] blk-throttle: enable io throttle for root in cgroup v2

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On 2021/09/09 22:08, Yu Kuai wrote:
We want to limit the overall iops/bps of the device in cgroup v2,
however "io.max" or "io.min" do not exist in root cgroup currently,
which makes it impossible.

This patch enables io throttle for root cgroup:
  - enable "io.max" and "io.min" in root
  - don't skip root group in tg_iops_limit() and tg_bps_limit()
  - don't skip root group in tg_conf_updated()

I'm not sure why this feature is disabled in the first place, is
there any problem or design constraint?

Ping...

BTW, sorry about the misspell of "io.low".
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
  block/blk-throttle.c | 13 ++-----------
  1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 55c49015e533..fffe072de538 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -302,9 +302,6 @@ static uint64_t tg_bps_limit(struct throtl_grp *tg, int rw)
  	struct throtl_data *td;
  	uint64_t ret;
- if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
-		return U64_MAX;
-
  	td = tg->td;
  	ret = tg->bps[rw][td->limit_index];
  	if (ret == 0 && td->limit_index == LIMIT_LOW) {
@@ -332,9 +329,6 @@ static unsigned int tg_iops_limit(struct throtl_grp *tg, int rw)
  	struct throtl_data *td;
  	unsigned int ret;
- if (cgroup_subsys_on_dfl(io_cgrp_subsys) && !blkg->parent)
-		return UINT_MAX;
-
  	td = tg->td;
  	ret = tg->iops[rw][td->limit_index];
  	if (ret == 0 && tg->td->limit_index == LIMIT_LOW) {
@@ -1430,9 +1424,8 @@ static void tg_conf_updated(struct throtl_grp *tg, bool global)
  		struct throtl_grp *parent_tg;
tg_update_has_rules(this_tg);
-		/* ignore root/second level */
-		if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent ||
-		    !blkg->parent->parent)
+		/* ignore root level */
+		if (!cgroup_subsys_on_dfl(io_cgrp_subsys) || !blkg->parent)
  			continue;
  		parent_tg = blkg_to_tg(blkg->parent);
  		/*
@@ -1771,7 +1764,6 @@ static struct cftype throtl_files[] = {
  #ifdef CONFIG_BLK_DEV_THROTTLING_LOW
  	{
  		.name = "low",
-		.flags = CFTYPE_NOT_ON_ROOT,
  		.seq_show = tg_print_limit,
  		.write = tg_set_limit,
  		.private = LIMIT_LOW,
@@ -1779,7 +1771,6 @@ static struct cftype throtl_files[] = {
  #endif
  	{
  		.name = "max",
-		.flags = CFTYPE_NOT_ON_ROOT,
  		.seq_show = tg_print_limit,
  		.write = tg_set_limit,
  		.private = LIMIT_MAX,




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