RFR: 8257901: ZGC: Take virtual memory usage into account when sizing heap [v2]

Per Liden pliden at openjdk.java.net
Wed Dec 9 09:41:49 UTC 2020


> 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 StefanK

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1696/files
  - new: https://git.openjdk.java.net/jdk/pull/1696/files/09bf660a..4370e0ed

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1696&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1696&range=00-01

  Stats: 23 lines in 7 files changed: 3 ins; 3 del; 17 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1696.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1696/head:pull/1696

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


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