RFR: 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines

[Poonam Bajaj]

Please review this simple change that adds null checks for memory in CgroupV1Subsystem.java.

Problem: After the backport of JDK-8250984,  there are places where memory.isSwapEnabled() is called. For example:

    public long getMemoryAndSwapFailCount() {
        if (!memory.isSwapEnabled()) {
            return getMemoryFailCount();
        }
        return SubSystem.getLongValue(memory, "memory.memsw.failcnt");
    }
 
But memory could be Null on some machines that have cgroup entries for CPU but not for memory. This would cause a NullPointerException when memory is accessed.

Fix: Add null checks for memory.

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Commit messages:
 - 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines

Changes: https://git.openjdk.java.net/jdk/pull/2269/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2269&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257746
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2269.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2269/head:pull/2269

PR: https://git.openjdk.java.net/jdk/pull/2269