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Subject[PATCH -next] blk-throttle: enable io throttle for root in cgroup v2
Date
RFC patch: https://lkml.org/lkml/2021/9/9/1432

There is a proformance problem in our environment:

A host can provide a remote device to difierent client. If one client is
under high io pressure, other clients might be affected.

Limit the overall iops/bps(io.max) from the client can fix the problem,
however, config files do not exist in root cgroup currently, which makes
it impossible.

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

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
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 7c462c006b26..ac25bfbbfe7f 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -156,9 +156,6 @@ 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) {
@@ -186,9 +183,6 @@ 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) {
@@ -1284,9 +1278,8 @@ 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);
/*
@@ -1625,7 +1618,6 @@ 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,
@@ -1633,7 +1625,6 @@ 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,
--
2.31.1
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