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

[Nick Gasson]

I noticed this when implementing JDK-8298482.  If UseAdaptiveSizePolicy and/or UseAdaptiveNUMAChunkSizing are enabled and UseLargePages is *not* enabled, part of the eden spaces managed by MutableNUMASpace end up bound to the wrong node.  This seems to be a regression caused by JDK-8283935, specifically the addition of


  set_page_size(alignment());


to MutableNUMASpace::initialize().  Previously the page size would have been equal to os::vm_page_size() unless UseLargePages was enabled.

In bias_region() we call os::free_memory() to uncommit a range of pages so that they can be later allocated on a different node, passing page_size() as the alignment_hint argument. However on Linux this does nothing if alignment_hint is greater than os::vm_page_size() and THP is not enabled, so the pages always remain bound to their original node (see os::pd_free_memory() in os_linux.cpp).

I think the solution here is to pass os::vm_page_size() as the alignment_hint when UseLargePages is disabled.

I tested SPECjbb on a dual-socket AArch64 system with -XX:+UseParallelGC -XX:+UseNUMA but otherwise default options and critical-jOPS improved by about 12% (averaged over several runs).

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Commit messages:
 - 8298642: ParallelGC -XX:+UseNUMA eden spaces allocated on wrong node

Changes: https://git.openjdk.org/jdk20/pull/33/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk20&pr=33&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298642
  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk20/pull/33.diff
  Fetch: git fetch https://git.openjdk.org/jdk20 pull/33/head:pull/33

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