RFR: 8294751: Zero: Allow larger default heaps [v2]

[Aleksey Shipilev]

On Thu, 6 Oct 2022 10:13:01 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Zero is currently defaulting to `MaxRAM=1G` on all machines. It is set in `compiler_globals.pd` under `#if !defined(COMPILER1) && !defined(COMPILER2) && !INCLUDE_JVMCI`.
>> 
>> Zero supports lots of GCs, and there is little sense to penalize it unnecessarily with too small heaps. After [JDK-8292847](https://bugs.openjdk.org/browse/JDK-8292847), this would allow G1 with reasonable heap size on most machines.
>> 
>> Motivational improvements, `SPECjvm2008:serial`:
>> 
>> 
>> # Baseline, G1
>> Serial.test  thrpt   10  1619.863 ± 16.694  ops/s
>> 
>> # Baseline, Serial
>> Serial.test  thrpt   10  1094.438 ± 20.425  ops/s
>> 
>> # Patched, G1
>> Serial.test  thrpt   10  1623.090 ± 17.553  ops/s
>> 
>> # Patched, Serial
>> Serial.test  thrpt   10  1624.531 ± 15.792  ops/s  ; <---- matches G1 now, because young is not tiny
>> 
>> 
>> Before:
>> 
>> 
>> $ build/linux-x86_64-zero-release/jdk/bin/java -Xlog:gc -Xlog:gc+init Alloc.java
>> [0.003s][info][gc     ] Using G1
>> ...
>> [0.005s][info][gc,init] Memory: 125G
>> ...
>> [0.005s][info][gc,init] Heap Region Size: 1M
>> [0.005s][info][gc,init] Heap Min Capacity: 8M
>> [0.005s][info][gc,init] Heap Initial Capacity: 16M
>> [0.005s][info][gc,init] Heap Max Capacity: 256M
>> 
>> 
>> After:
>> 
>> 
>> $ build/linux-x86_64-zero-release/jdk/bin/java -Xlog:gc -Xlog:gc+init Alloc.java
>> [0.003s][info][gc     ] Using G1
>> ...
>> [0.007s][info][gc,init] Memory: 125G
>> ...
>> [0.007s][info][gc,init] Heap Region Size: 16M
>> [0.007s][info][gc,init] Heap Min Capacity: 16M
>> [0.007s][info][gc,init] Heap Initial Capacity: 2016M
>> [0.007s][info][gc,init] Heap Max Capacity: 30208M
>
> Aleksey Shipilev 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:
> 
>  - Move to compiler_globals_pd.hpp
>  - Merge branch 'master' into JDK-8294751-zero-larger-heaps
>  - Fix

Thanks!

-------------

PR: https://git.openjdk.org/jdk/pull/10552