[jdk20] RFR: 8298642: ParallelGC -XX:+UseNUMA eden spaces allocated on wrong node

[Albert Mingkun Yang]

On Wed, 14 Dec 2022 14:23:01 GMT, Nick Gasson <ngasson at openjdk.org> wrote:

> In bias_region() we call os::free_memory() to uncommit a range of pages

Just for the record, `os::free_memory()` does not uncommit any mem. Instead, it calls `commit_memory` to overwrite existing mmapings.

I believe the reason why this fix works is that at startup eden-space is committed (within young-gen) using a single `mmap` call (`PSVirtualSpace::expand_by`), resulting into one mmapping, which is later overwritten (in `MutableNUMASpace::bias_region`) to 2 (assuming 2 numa nodes) mmappings that can bind to diff numa nodes.

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PR: https://git.openjdk.org/jdk20/pull/33