RFR: JDK-8266490: Extend the OSContainer API to support the pids controller of cgroups [v2]

[Matthias Baesken]

On Wed, 23 Jun 2021 13:37:59 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> Hello, please review this PR; it extend the OSContainer API in order to also support the pids controller of cgroups.
>> 
>> I noticed that unlike the other controllers "cpu", "cpuset", "cpuacct", "memory"  on some older Linux distros (SLES 12.1, RHEL 7.1) the pids controller might not be there (or not fully supported) so it was added as optional  , see the coding
>> 
>> 
>>   if (!cg_infos[PIDS_IDX]._data_complete) {
>>     log_debug(os, container)("Optional cgroup v1 pids subsystem not found");
>>     // keep the other controller info, pids is optional
>>   }
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adjustments following Severins comments

Hi Severin , thanks for all the comments.   I prepared a second version with those changes
added a couple of log_is_enabled checks like you suggested
moved limit_from_str to CgroupSubsystem
added helpers pids_max_val()  and swicthed to GET_CONTAINER_INFO_CPTR
pids_max() now returns -1 for unlimited/max , and the -3 is gone
moved limitFromString java coding to src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystem.java
added a better comment to test/hotspot/jtreg/containers/cgroup/CgroupSubsystemFactory.java about pids hiearchy values

Regarding your questions about tests, I run the exisiting docker/cgroup related tests; and also checked 
the hs_err output (on SLES/Ubuntu)  for new added "maximum number of tasks"  (this is present because systemd cgroup usage).
But I think that the testing needs to be enhanced (e.g. with some added docker tests?).  Do you have some good suggestions
where I could look at existing (docker?) tests and  adjust those for the new pids.max ?

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PR: https://git.openjdk.java.net/jdk/pull/4518