RFR: JDK-8306441: Two phase segmented heap dump [v21]

[Chris Plummer]

On Tue, 1 Aug 2023 05:50:42 GMT, Yi Yang <yyang at openjdk.org> wrote:

>> ### Motivation and proposal
>> Hi, heap dump brings about pauses for application's execution(STW), this is a well-known pain. JDK-8252842 have added parallel support to heapdump in an attempt to alleviate this issue. However, all concurrent threads competitively write heap data to the same file, and more memory is required to maintain the concurrent buffer queue. In experiments, we did not feel a significant performance improvement from that.
>> 
>> The minor-pause solution, which is presented in this PR, is a two-phase segmented heap dump:
>> 
>> - Phase 1(STW): Concurrent threads directly write data to multiple heap files.
>> - Phase 2(Non-STW): Merge multiple heap files into one complete heap dump file. This process can happen outside safepoint.
>> 
>> Now concurrent worker threads are not required to maintain a buffer queue, which would result in more memory overhead, nor do they need to compete for locks. The changes in the overall design are as follows:
>> 
>> ![image](https://github.com/openjdk/jdk/assets/5010047/77e4764a-62b5-4336-8b45-fc880ba14c4a)
>> <p align="center">Fig1. Before</p>
>> 
>> ![image](https://github.com/openjdk/jdk/assets/5010047/931ab874-64d1-4337-ae32-3066eed809fc)
>> <p align="center">Fig2. After this patch</p>
>> 
>> ### Performance evaluation
>> | memory | numOfThread | CompressionMode | STW | Total |
>> | -------| ----------- | --------------- | --- | ---- |
>> | 8g | 1 T | N | 15.612 | 15.612 |
>> | 8g | 32 T | N | 2.561725 | 14.498 |
>> | 8g | 32 T | C1 | 2.3084878 | 14.198 |
>> | 8g | 32 T | C2 | 10.9355128 | 21.882 |
>> | 8g | 96 T | N | 2.6790452 | 14.012 |
>> | 8g | 96 T | C1 | 2.3044796 | 3.589 |
>> | 8g | 96 T | C2 | 9.7585151 | 20.219 |
>> | 16g | 1 T | N | 26.278 | 26.278 |
>> | 16g | 32 T | N | 5.231374 | 26.417 |
>> | 16g | 32 T | C1 | 5.6946983 | 6.538 |
>> | 16g | 32 T | C2 | 21.8211105 | 41.133 |
>> | 16g | 96 T | N | 6.2445556 | 27.141 |
>> | 16g | 96 T | C1 | 4.6007096 | 6.259 |
>> | 16g | 96 T | C2 | 19.2965783 | 39.007 |
>> | 32g | 1 T | N | 48.149 | 48.149 |
>> | 32g | 32 T | N | 10.7734677 | 61.643 |
>> | 32g | 32 T | C1 | 10.1642097 | 10.903 |
>> | 32g | 32 T | C2 | 43.8407607 | 88.152 |
>> | 32g | 96 T | N | 13.1522042 | 61.432 |
>> | 32g | 96 T | C1 | 9.0954641 | 9.885 |
>> | 32g | 96 T | C2 | 38.9900931 | 80.574 |
>> | 64g | 1 T | N | 100.583 | 100.583 |
>> | 64g | 32 T | N | 20.9233744 | 134.701 |
>> | 64g | 32 T | C1 | 18.5023784 | 19.358 |
>> | 64g | 32 T | C2 | 86.4748377 | 172.707 |
>> | 64g | 96 T | N | 26.7374116 | 126.08 |
>> | 64g | ...
>
> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   test failure on mac

test/hotspot/jtreg/serviceability/HeapDump/IntegrityHeapDumpTest.java line 84:

> 82:                 .addToolArg(heapDumpFile.getAbsolutePath());
> 83: 
> 84:         ProcessBuilder processBuilder = new ProcessBuilder(launcher.getCommand());

Can you explain this change? This will result in the test not being run with sudo in cases where sudo is necessary. Before we get here we already checked if we need sudo (not running as root) and verified that passwordless sudo is supported. Otherwise the test is skipped and would never get here. So if sudo is required, the test will fail to attach to the debuggee. Note you might not see this issue if you have DevSecurityMode enabled. See [JDK-8313357](https://bugs.openjdk.org/browse/JDK-8313357)

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PR Review Comment: https://git.openjdk.org/jdk/pull/13667#discussion_r1280948269