how to limit scst read/wrtie iops with cgroup-v2?

[zhujing3]

Proceed as follows:
using cgroup-v1

on scst server:

1. add device to vdisk hankder
2. create a iscsi target,add lun & initor
3. echo "230:256 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device

on client:

1. login iscsi target
2. run dd: dd iflag=direct if=/dev/sdb of=/dev/null bs=4k count=1024

the results are consistent with expectations：

1024+0 records in
1024+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 4.00212 s, 1.0 MB/s

=================
cgroup v2:

i have add all iscsi/scst/lun-name-process，even all system process to cgroup.procs ,
finally it's only works on scst-server :

dd iflag=direct if=/dev/zd256 of=/dev/null bs=4k count=1024 
1024+0 records in
1024+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 4.00212 s, 1.0 MB/s

on client, doesn't work at all

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the problem：

how to find those process for scst read/write on disk ?