Class unloading in jdk15

[Zhengyu Gu]

On 5/13/20 7:07 AM, Aleksey Shipilev wrote:
> On 5/12/20 8:25 PM, Aleksey Shipilev wrote:
>> Hi again,
>>
>> On 4/21/20 2:09 PM, Vicente Rossello wrote:
>>> Let me know if I can provide something else
>>
>> If you are able, could you please take the latest jdk-jdk binary:
>>    https://builds.shipilev.net/openjdk-jdk/openjdk-jdk-latest-linux-x86_64-release.tar.xz
>>
>> ...and run it with class unloading enabled and -Xlog:gc+stats?
>>
>> It would now print more verbose stats around class unloading, so we can take a look which part is
>> really problematic.
> 
> Vincente sent me the logs privately.

Did it still run into degenerated GC?

-Zhengyu

> 
> Here are the salient parts, Code Roots work dominates when outliers happen:
> 
> [2020-05-13T09:16:54.856+0000] Concurrent Class Unloading    2563469 us
> [2020-05-13T09:16:54.856+0000]   Unlink Stale                2563068 us
> [2020-05-13T09:16:54.856+0000]     System Dictionary            1758 us
> [2020-05-13T09:16:54.856+0000]     Weak Class Links            27652 us
> [2020-05-13T09:16:54.856+0000]     Code Roots                2533655 us
> [2020-05-13T09:16:54.856+0000]   Rendezvous                      105 us
> [2020-05-13T09:16:54.856+0000]   Purge Unlinked                  291 us
> [2020-05-13T09:16:54.856+0000]     Code Roots                    264 us
> [2020-05-13T09:16:54.856+0000]     CLDG                           27 us
> [2020-05-13T09:16:54.856+0000]     Exception Caches                0 us
> 
> [2020-05-13T09:17:06.522+0000] Concurrent Class Unloading    2305834 us
> [2020-05-13T09:17:06.522+0000]   Unlink Stale                2305223 us
> [2020-05-13T09:17:06.522+0000]     System Dictionary            2080 us
> [2020-05-13T09:17:06.522+0000]     Weak Class Links            32926 us
> [2020-05-13T09:17:06.522+0000]     Code Roots                2270215 us
> [2020-05-13T09:17:06.522+0000]   Rendezvous                       59 us
> [2020-05-13T09:17:06.522+0000]   Purge Unlinked                  533 us
> [2020-05-13T09:17:06.522+0000]     Code Roots                    272 us
> [2020-05-13T09:17:06.522+0000]     CLDG                          260 us
> [2020-05-13T09:17:06.522+0000]     Exception Caches                0 us
> 
> [2020-05-13T09:17:08.512+0000] Concurrent Class Unloading    1190682 us
> [2020-05-13T09:17:08.512+0000]   Unlink Stale                1189699 us
> [2020-05-13T09:17:08.512+0000]     System Dictionary            2995 us
> [2020-05-13T09:17:08.512+0000]     Weak Class Links            48842 us
> [2020-05-13T09:17:08.512+0000]     Code Roots                1137860 us
> [2020-05-13T09:17:08.512+0000]   Rendezvous                       91 us
> [2020-05-13T09:17:08.512+0000]   Purge Unlinked                  886 us
> [2020-05-13T09:17:08.512+0000]     Code Roots                    229 us
> [2020-05-13T09:17:08.512+0000]     CLDG                          657 us
> [2020-05-13T09:17:08.512+0000]     Exception Caches                0 us
> 
> [2020-05-13T09:17:26.046+0000] Concurrent Class Unloading    3125368 us
> [2020-05-13T09:17:26.046+0000]   Unlink Stale                3123611 us
> [2020-05-13T09:17:26.046+0000]     System Dictionary            2591 us
> [2020-05-13T09:17:26.046+0000]     Weak Class Links            45748 us
> [2020-05-13T09:17:26.046+0000]     Code Roots                3075268 us
> [2020-05-13T09:17:26.046+0000]   Rendezvous                      315 us
> [2020-05-13T09:17:26.046+0000]   Purge Unlinked                 1436 us
> [2020-05-13T09:17:26.046+0000]     Code Roots                   1280 us
> [2020-05-13T09:17:26.046+0000]     CLDG                          156 us
> [2020-05-13T09:17:26.046+0000]     Exception Caches                0 us
>