On Fri, 16 May 2025 08:36:22 GMT, Albert Mingkun Yang <ay...@openjdk.org> wrote:
>> This patch refines Parallel's sizing strategy to improve overall memory >> management and performance. >> >> The young generation layout has been reconfigured from the previous >> `eden-from/to` arrangement to a new `from/to-eden` order. This new layout >> facilitates young generation resizing, since we perform resizing after a >> successful young GC when all live objects are located at the beginning of >> the young generation. Previously, resizing was often inhibited by live >> objects residing in the middle of the young generation (from-space). The new >> layout is illustrated in `parallelScavengeHeap.hpp`. >> >> `NumberSeq` is now used to track various runtime metrics, such as >> minor/major GC pause durations, promoted/survived bytes after a young GC, >> highest old generation usage, etc. This tracking primarily lives in >> `AdaptiveSizePolicy` and its subclass `PSAdaptiveSizePolicy`. >> >> GC overhead checking, which was previously entangled with adaptive resizing >> logic, has been extracted and is now largely encapsulated in >> `ParallelScavengeHeap::is_gc_overhead_limit_reached`. >> >> ## Performance evaluation >> >> - SPECjvm2008-Compress shows ~8% improvement on Linux/AArch64 and Linux/x64 >> (restoring the regression reported in >> [JDK-8332485](https://bugs.openjdk.org/browse/JDK-8332485) and >> [JDK-8338689](https://bugs.openjdk.org/browse/JDK-8338689)). >> - Fixes the surprising behavior when using a non-default (smaller) value of >> `GCTimeRatio` with Heapothesys/Hyperalloc, as discussed in [this >> thread](https://mail.openjdk.org/pipermail/hotspot-gc-dev/2024-November/050146.html). >> - Performance is mostly neutral across other tested benchmarks: **DaCapo**, >> **SPECjbb2005**, **SPECjbb2015**, **SPECjvm2008**, and **CacheStress**. The >> number of young-gc sometimes goes up a bit and the total heap-size decreases >> a bit, because promotion-size-to-old-gen goes down with the more effective >> eden/survivor-space resizing. >> >> PS: I have opportunistically set the obsolete/expired version to 25/26 for >> now. I will update them accordingly before merging. >> >> Test: tier1-8 > > Albert Mingkun Yang has updated the pull request with a new target base due > to a merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains three additional > commits since the last revision: > > - review > - Merge branch 'master' into pgc-size-policy > - pgc-size-policy src/hotspot/share/gc/parallel/parallelScavengeHeap.cpp line 51: > 49: #include "oops/oop.inline.hpp" > 50: #include "runtime/cpuTimeCounters.hpp" > 51: #include "runtime/globals_extension.hpp" Don't see why it is needed. src/hotspot/share/gc/parallel/parallelScavengeHeap.cpp line 404: > 402: collect_at_safepoint(!should_run_young_gc); > 403: > 404: if (is_gc_overhead_limit_reached()) { Maybe want to adopt current algorithm, start to clear soft references when approaching gc overhead limit? Running a full gc and clearing all soft references without retrying allocation and throws OOM, seems a bit harsh. People still use soft references for caches, reclaim soft references could potentially free large amount of memory. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2087170321 PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2087828140
