RFR 8250984: Memory Docker tests fail on some Linux kernels w/o swap limit capabilities

[Harold Seigel]

Hi Bob,

I came up with these ways to handle the test failures when swap limiting 
is disabled (JDK-8250984).  Please let me know if any of them sound viable.

One way is to add logging to CgroupSubsystemController when it fails to 
open a file such as .../memsw.linit_in_bytes.  The tests would enable 
logging and then look for these messages to determine if swap limiting 
was disabled.  This is yet another string for the tests to parse, but 
the JDK controls the contents of the strings, so there is less concern 
about them changing.  Here's a webrev showing this potential change:

    http://cr.openjdk.java.net/~hseigel/bug_8250984.dkr.log/webrev/index.html

Another way is for methods such as 
CgroupSubsystemController.getLongEntry() to return a -2 status, 
indicating not-implemented, when it cannot access a file.  The callers 
of getLongEntry() could then decide whether or not to propagate that 
status back to their callers, or return some other default.  A partial 
webrev for that change is here:

    http://cr.openjdk.java.net/~hseigel/bug_8250984.dkr.RetVal/webrev/index.html

We could also change methods such as 
CgroupV1Subsystem.getMemoryAndSwapLimit() to explicitly check for the 
existence of the files they want to read from and return -2 if the check 
fails.  This may have a performance impact?

Thanks, Harold

On 9/1/2020 12:04 PM, Bob Vandette wrote:
> I really dislike encoding all these strings in our tests that could possibly change.
>
> I wish we did something like check for the existence of /sys/fs/cgroup/memory/memsw.limit_in_bytes
> assuming that this file is not present when swap limiting is disabled.  The problem with this approach
> and yours is that we need to make that these fixes we can run on docker, podman, cgroupv1 and cgroupv2.
>
> Others are struggling with these types of issues …
>
> https://github.com/containers/podman/issues/6365
>
> The Metrics API I added provides for the possibility that the call to getMemoryAndSwapLimit
> could fail.  Perhaps the test should be checking for not supported and fix the API implementation
> to report the correct error (if it doesn’t already).
>
>      /**
>       * Returns the maximum amount of physical memory and swap space,
>       * in bytes, that can be allocated in the Isolation Group.
>       *
>       * @return The maximum amount of memory in bytes or -1 if
>       *         there is no limit set or -2 if this metric is not supported.
>       *
>       */
>      public long getMemoryAndSwapLimit();
>
> My .02$
>
> Bob.
>
>> On Sep 1, 2020, at 11:31 AM, Harold Seigel <harold.seigel at oracle.com> wrote:
>>
>> Hi,
>>
>> Please review this fix to enable docker tests TestMemoryAwareness.java and TestDockerMemoryMetrics.java to run on Linux kernels configured without swap limit capabilities.
>>
>> Open Webrev: http://cr.openjdk.java.net/~hseigel/bug_8250984.dkr/webrev/index.html
>>
>> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8250984
>>
>> The modified tests were run on Linux kernels with and without swap limit capabilities.
>>
>> Thanks, Harold
>>