[rhelv6-list] Limiting pvmove speed with control groups doesn't work as expected

[Brian Long (brilong)]

Gianluca,

This is an interesting thread and I’m glad you found a solution.  I wonder if newer RHEL 6 kernels or if the RHEL 7 kernel provides the needed mechanism to tie pvmove to the kernel thread kcopyd such that your first technique would work without manually finding the kcopyd PID each time you call pvmove.

/Brian/
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       Brian Long                             |       |
       Research Triangle Park, NC         . | | | . | | | .
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                                              C I S C O

On Jul 26, 2016, at 11:51 AM, Gianluca Cecchi <gianluca.cecchi at gmail.com<mailto:gianluca.cecchi at gmail.com>> wrote:

With iotop I see the PID of kcopyd that starts right after pvmove command.... (the kcopyd pid is different every pvmove run, not a fixed process)

[root at dbatest1 ~]# ps -ef|grep 11139
root     11139     2  1 17:40 ?        00:00:02 [kcopyd]
root     17103 19305  0 17:43 pts/0    00:00:00 grep 11139

BTW, kcopyd is child of kthreadd:

root         2     0  0 Jun29 ?        00:00:00 [kthreadd]

So I put kcopyd process into the control group too

# echo 11139 > /cgroup/blkio/30M/tasks

so that I now have pvmove process and kcopyd process

[root at dbatest1 ~]# cat /cgroup/blkio/30M/tasks
11139
12765

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