Overhead of -XX:+UseContainerSupport

[Florian Weimer]

On OpenJDK 12, running

  jshell -J-Xlog:container*=trace 

suggests that the container memory amount is not cached at all.  (I
use jshell as a non-trivial example program, the issue appears to
affect everything.)

strace also shows lots of openat calls for paths like this one:

/sys/fs/cgroup/memory/user.slice/user-1000.slice/session-1.scope/memory.limit_in_bytes

All this goes away with -XX:-UseContainerSupport, but the default is
enabled.

These calls appear to be triggered by the Hotspot compiler (they go
away with -Xint), so in a sense this is just a warmup effect.  But I
do wonder if there is a better way of doing this.