RFR: 8317371: GenShen: Needs improved support for humongous allocation [v16]

[Kelvin Nilsen]

On Mon, 23 Oct 2023 21:29:17 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Several improvements:
>> 1. If there is a humongous allocation failure, go immediately to Full GC rather than trying 64 degenerated GC first
>> 2. Reduce likelihood of humongous allocation errors by:
>>     a. Allocating regular objects from top end of memory while allocating humongous from bottom end of memory
>>     b. (Especially) in the case that regular regions that are promoted in place reside within the bottom end of memory, detect that old-gen memory has become fragmented and trigger old-gen GC, which will make a special effort to move these out-of-place old-gen regions to higher addresses.
>
> Kelvin Nilsen has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Fix merge conflict
>  - Remove redundant option to request dump of memory logs

> > If there is a humongous allocation failure, go immediately to Full GC rather than trying 64 degenerated GC first
> 
> Can we set `ShenandoahFullGCThreshold` back to the upstream default of 3 now? It should have been done when we merged [openjdk/jdk#15500](https://github.com/openjdk/jdk/pull/15500) .

This has been reverted to 3.

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PR Comment: https://git.openjdk.org/shenandoah/pull/336#issuecomment-1776117404