RFR: 8257901: ZGC: Take virtual memory usage into account when sizing heap [v3]

Thomas Schatzl tschatzl at openjdk.java.net
Wed Dec 9 12:10:50 UTC 2020


On Wed, 9 Dec 2020 12:08:31 GMT, Per Liden <pliden at openjdk.org> wrote:

>> MaxVirtMemFraction limits the amount of address space the GC should use for the heap. This is used by the heuristics in Arguments::set_heap_size() to select an appropriate default max heap size. However, that heuristic can select a max heap size that will not fit with ZGC, since ZGC uses additional address space (for multi-mapping and the virtual-to-physical ratio). As a result, if the address space is limited, and -Xmx is not specified, then ZGC might refuse to start with the error:
>> 
>> "Failed to reserve enough address space for Java heap"
>> 
>> I propose we abstract MaxVirtMemFraction to make it configurable for each GC, so that the heuristics in Arguments::set_heap_size() will pick a default max heap size that also works for ZGC.
>> 
>> Testing: Manual testing using different ulimit -v sizes.
>
> Per Liden has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review

Marked as reviewed by tschatzl (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1696


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