On Fri, 27 May 2022 07:22:11 GMT, Thomas Stuefe <[email protected]> wrote:
>>> I think the right fix is to just convert the MetaspacePool into
>>> NonClassMetaspacePool and only report the non-class values.
>>
>> Yes, it's okay for me. But I have another concern.
>>
>> The compressed class pool is not directly used by other VM components.
>> However, memory pools are exposed via java management APIs. At JDK level,
>> users could obtain memory pools and choose a specified pool by name. If
>> adapting the first solution, I guess it's somewhat strange for users to
>> understand what is `Non Class Space`:
>>
>> private static MemoryPoolMXBean getMemoryPool(String name) {
>> List<MemoryPoolMXBean> pools =
>> ManagementFactory.getMemoryPoolMXBeans();
>> for (MemoryPoolMXBean pool : pools) {
>> if (pool.getName().equals(name)) {
>> return pool;
>> }
>> }
>>
>> throw new RuntimeException("Expected to find a memory pool with name
>> " + name);
>> }
>> public static void foo() {
>> MemoryPoolMXBean a = getMemoryPool("Compressed Class Space");
>> MemoryPoolMXBean a = getMemoryPool("Non Class Space");
>> }
>>
>> If we remove `CompressedClassSpace`, we can only
>> `getMemoryPool("Metaspace")`. Although metaspace is not baked in the
>> specification, IMHO it's easier for developers to understand what is
>> `metaspace` compared to the concepts of `Non Class Space` and `Compressed
>> Class Space`.
>
>>
>> If we remove `CompressedClassSpace`, we can only
>> `getMemoryPool("Metaspace")`. Although metaspace is not baked in the
>> specification, IMHO it's easier for developers to understand what is
>> `metaspace` compared to the concepts of `Non Class Space` and `Compressed
>> Class Space`.
>
> I personally think that would be totally fine.
> @tstuefe could you take a look at the test changes. Since we can no longer
> query the compressed class space individually, I think the tests may become
> more lenient than before. For example,
> memoryUsageSmallComp/TestDescription.java uses
> `MemoryUsageTest::checkForNotGrowing()` which monitors the used bytes in
> `MetaspaceBaseGC::pool.getUsage().getUsed()`
>
> * Before this PR, it checks that the usage of the compressed klass space
> doesn't grow.
> * After this PR, it will allow the compresed klass space to grow, as long as
> the "other" meta space shrinks by a similar amount.
>
> Is this OK? Or should we add a new whitebox API to query the compressed vs
> meta space?
Sorry for the long delay, I was not at work.
I think you may be right, we need a replacement for the old memory bean for
these tests. Whitebox seems easiest.
-------------
PR: https://git.openjdk.org/jdk/pull/8831
