RFR: 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible) [v4]

[Severin Gehwolf]

On Mon, 5 Oct 2020 08:59:34 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java line 80:
>> 
>>> 78:      */
>>> 79:     private static final Pattern MOUNTINFO_PATTERN =
>>> 80:
>>> Pattern.compile("^[^\\s]+\\s+[^\\s]+\\s+[^\\s]+\\s+([^\\s]+)\\s+([^\\s]+)\\s+[^-]+-\\s+([^\\s]+)\\s+.*$");
>> 
>> Only group_3 = fstype is used in the pattern, right?
>
> Yes. I've removed unused groups now, though.
> 
> Originally, my thinking was that `mount root` and `mount path` would be useful too so I kept it in. It would certainly
> be useful for getting rid of reading `/proc/self/mountinfo` twice on the Java side. As a future enhancement we could do
> away with double parsing of mount info by keeping track of relevant cgroup controller info. I've filed
> [JDK-8254001](https://bugs.openjdk.java.net/browse/JDK-8254001) to track this.

The latest version goes back to using all three as it's beneficial to track that info and use it later on for
instantiating the version specific objects.

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PR: https://git.openjdk.java.net/jdk/pull/485