CODEWITHSUNDEEP
iolinux-kerneloperating-systemcgroups
user1734905
user1734905

Reputation: 333

cgroup blkio files cannot be written

I'm trying to control I/O bandwidth by using cgroup blkio controller.

Cgroup has been setup and mounted successfully, i.e. calling grep cgroup /proc/mounts

returns:

....
cgroup /sys/fs/cgroup/blkio cgroup rw,relatime,blkio 0 0
...

I then make a new folder in the blkio folder and write to the file blkio.throttle.read_bps_device, as follows:

1. mkdir user1; cd user1
2. echo "8:5 10485760" > blkio.throtlle.read_bps_device
----> echo: write error: Invalid argument

My device major:minor number is correct from using df -h and ls -l /dev/sda5 for the storage device.

And I can still write to file that requires no device major:minor number, such as blkio.weight (but the same error is thrown for blkio.weigth_device)

Any idea why I got that error?

Upvotes: 3

Views: 4724

Answers (1)

askb
askb

Reputation: 6768

Not sure which flavour/version of Linux you are using, on RHEL 6.x kernels, this was did not work for some reason, however it worked when I compiled on a custom kernel on RHEL and on other Fedora versions without any issues.

To check if supported on your kernel, run lssubsys -am | grep blkio. Check the path if you can file the file blkio.throttle.read_bps_device

However, here is an example of how you can do it persistently, set a cgroups to limit the program not to exceed more than 1 Mibi/s:

  1. Get the MARJOR:MINOR device number from /proc/partitions
   `cat /proc/partitions | grep vda` 
     major minor  #blocks  name
     252        0   12582912 vda  --> this is the primary disk (with MAJOR:MINOR -> 8:0)

  1. Now if you want to limit your program to 1mib/s (convert the value to bytes/s) as follows. => 1MiB/s => 1024 kiB/1MiB * 1024 B/s = 1048576 Bytes/sec

  2. Edit /etc/cgconfig.conf and add the following entry

group ioload {
  blkio.throttle.read_bps_device = "252:0 1048576" 
  }
}
  1. Edit /etc/cgrules.conf

*: blkio ioload

  1. Restart the required services
`chkconfig {cgred,cgconfig} on;`
`service {cgred,cgconfig} restart`

Refer: blkio-controller.txt

hope this helps!

Upvotes: 6

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