On Wed, 2 Aug 2023 14:33:28 GMT, Yi Yang <yy...@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: >> >>  >> <p align="center">Fig1. Before</p> >> >>  >> <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: > > whitespace
Yes thanks, that makes VM_HeapDumper::doit() simpler which is completely the idea 8-) OK in this new VM_HeapDumper::can_parallel_dump there is a use for num_requested_dump_thread variable, as we print the requested and final thread counts. We were not doing that before, but it is useful. I didn't see the change of _num_dump_threads affecting whether this was or was not a parallel dump, but not important if we go with your new method. (we should call it num_requested_dump_threads and then we are probably done here 8-) ) ------------- PR Comment: https://git.openjdk.org/jdk/pull/13667#issuecomment-1665457390
