Can't throttle IO on cgroup. Says "No such device" when device exists. What could be wrong? [closed] - linux

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Instructions I followed: https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html
Script I ran:
BYTES_PER_SEC=1048576;
MAJOR=259
MINOR=1
echo "device name:"
udevadm info -rq name /sys/dev/block/$MAJOR:$MINOR
echo ""
echo "device numbers:"
echo $MAJOR:$MINOR;
echo ""
sudo mount -t cgroup -o blkio none /sys/fs/cgroup/blkio;
sudo echo "COMMAND TO BE EXECUTED:";
sudo echo "$MAJOR:$MINOR $BYTES_PER_SEC";
sudo echo "$MAJOR:$MINOR $BYTES_PER_SEC" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
sudo echo "$MAJOR:$MINOR $BYTES_PER_SEC" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device
Output:
~/Desktop >>> sudo ./test.sh [1]
[sudo] password for brian:
/dev/nvme0n1p1
device name: 259:1
mount: /sys/fs/cgroup/blkio: none already mounted on /sys/fs/bpf.
COMMAND TO BE EXECUTED:
259:1 1048576
echo: write error: No such device
echo: write error: No such device
Not sure what could be wrong. I'm also using NixOS here so not sure if that will actually effect the results.

Answer 1

The error occurs because the only way to throttle IO using cgroups version 1 is to use a device that is physical. The major and minor version numbers I used above are for a partition. You need to pick the major and minor numbers for the physical device that HOLDS the partition.