RFR: 8238665: Add JFR event for direct memory statistics

[Erik Gahlin]

Hi Denghui,

Thanks for the explanation.

I think the default interval could be increased to once every 5 seconds.

Have you run the all the tests in test/jdk/jdk/jfr? I would expect 
TestDefaultConfigurations to have failed unless modified.

Thanks
Erik

On 2020-02-26 14:40, 董登辉(卓昂) wrote:
> PING: Could you review it?
> Bug: https://bugs.openjdk.java.net/browse/JDK-8238665
> Webrev: http://cr.openjdk.java.net/~ddong/8238665/webrev.01/
>
>     ------------------------------------------------------------------
>     From:董登辉(卓昂) <denghui.ddh at alibaba-inc.com>
>     Send Time:2020年2月11日(星期二) 16:13
>     To:Erik Gahlin <erik.gahlin at oracle.com>
>     Cc:hotspot-jfr-dev <hotspot-jfr-dev at openjdk.java.net>
>     Subject:Re: RFR: 8238665: Add JFR event for direct memory statistics
>
>     Hi Erik,
>
>     Thanks for the review. See answers embedded.
>
>     New webrev: http://cr.openjdk.java.net/~ddong/8238665/webrev.01/
>
>     On Feb 11, 2020, at 1:52 AM, Erik Gahlin <erik.gahlin at oracle.com
>     <mailto:erik.gahlin at oracle.com>> wrote:
>
>     Hi Denghiu,
>
>     Can you explain when this event can be useful, i.e. when
>     troubleshooting x etc.? This makes it easier to determine if the
>     event should be on by default, if it is worth the increased
>     startup cost that the instrumentation creates and what a
>     reasonable period for the event should be.
>
>     Many Java middleware(e.g. Netty) and applications use direct
>     memory for achieving higher performance,  if java process use too
>     much direct memory, some exceptions will occur, such as
>     oom-killer. Hence, it’s necessary to monitor it,  and we use JMX
>     to monitor it in our production environment currently.
>
>     src/jdk.jfr/share/classes/jdk/jfr/events/DirectMemoryStatisticsEvent.java:
>
>     @Label("TotalCapacity") -> @Label("Total Capacity")
>     @Label("MemoryUsed") -> @Label("Memory Used”)
>
>     Updated
>
>     What is meant by 'limit'? Could we have a better field name and/or
>     description that explains what this fields contains, because it is
>     not obvious from that name. Fields that contains bytes, should
>     have the DataAmount; annotation.
>
>     What is the value if -XX:MaxDirectMemorySize has not been set?
>
>     limit -> maxCapacity
>
>      if -XX:MaxDirectMemorySize has not been set, the value
>     of Runtime.getRuntime().maxMemory() will be used.
>
>     Can you make the event class final.
>
>     Updated
>
>     @StackTrace(false) should not be needed.
>
>     Removed
>
>     test/jdk/jdk/jfr/event/runtime/TestDirectMemoryStatisticsEvent.java:
>
>     Use try-with-resources on the Recording object.
>
>     Updated
>
>     Thanks
>     Denghui Dong
>
>     Thanks
>     Erik
>
>     On 2020-02-07 06:24, Denghui Dong wrote:
>     Hi,
>
>     Could I have a review of a change that adds JFR event for direct
>     memory statistics
>
>     Bug: https://bugs.openjdk.java.net/browse/JDK-8238665
>     Webrev: http://cr.openjdk.java.net/~ddong/8238665/webrev.00/
>     Test:
>     test/jdk/jdk/jfr/event/runtime/TestDirectMemoryStatisticsEvent.java
>
>     Thanks
>     Denghui Dong
>