RFR: 8239559: Cgroups: Incorrect detection logic on some systems

[Baesken, Matthias]

Hi Severin,   8239559/02   looks  generally good .

However I wonder about this :

I have a SLES15 aarch64 system with these settings :

 more /proc/cgroups 
#subsys_name	hierarchy	num_cgroups	enabled
cpuset	6	1	1
cpu	8	1	1
cpuacct	8	1	1
blkio	5	1	1
memory	9	1	1
devices	2	91	1
freezer	4	1	1
net_cls	3	1	1
perf_event	11	1	1
net_prio	3	1	1
hugetlb	10	1	1
pids	12	105	1
rdma	7	1	1


(so no hierarchy  0 )

However these information indicates the cgroup2 is supported :

fgrep cgroup2 /proc/self/mountinfo
29 28 0:25 / /sys/fs/cgroup/unified rw,nosuid,nodev,noexec,relatime shared:5 - cgroup2 cgroup rw

grep cgroup /proc/filesystems
nodev	cgroup
nodev	cgroup2


But the comment    in

http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8239559/02/webrev/src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java.frames.html


says 

 102         // For cgroups v2 all controllers need to have zero hierarchy id
 103         // and /proc/self/mountinfo needs to have at least one cgroup filesystem
 104         // mounted.


Should this comment be adjusted ?
On the system above  we  have no 0  in  /proc/cgroups   however  it seems to me the system supports  cgroug v2 ?


Best regards, Matthias



> 
> > I still need a *R*eviewer. Matthias, would you be willing to?
> 
> Hi Severin,   I can look into it tomorrow  .
> 
> Best regards, Matthias
> 
> 
> 
> >
> > On Mon, 2020-02-24 at 10:28 -0500, Bob Vandette wrote:
> > > > > If you don’t have access to the information required to get metrics, I
> > just assumed that
> > > > > you would return NULL in CgroupSubsystemFactory.create() rather
> > than making the
> > > > > assumption that it works only to fail later.
> > > >
> > > > You are right. It makes little sense to continue in that case. Updated
> > > > webrev:
> > > > http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-
> > 8239559/02/webrev/
> > >
> > > Looks good.
> >
> > Thanks for the review.
> >
> > I still need a *R*eviewer. Matthias, would you be willing to?
> >
> > Thanks,
> > Severin
> >