RFR: 8259231: Epsilon: improve performance under contention during virtual space expansion [v3]

[Aleksey Shipilev]

On Wed, 6 Jan 2021 01:31:10 GMT, Lehua Ding <github.com+13173904+lhtin at openjdk.org> wrote:

>> Hi all,
>> 
>> The `EpsilonHeap::allocate_work` method maybe can be fixed and improved by this:
>> 1. it can prevent allocate failure by retry `_space->par_allocate` before expanding virtual space,  when there not enough virtual space but another thread expanding succeeded just and has enough space.
>> 2. it can reduce the lock time by move `res = _space->par_allocate(size);` out of lock scope.
>> 
>> Test on macosx-x86_64-server-{release, fastdebug, slowdebug} with current test case.
>
> Lehua Ding has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Epsilon: clean trailing whitespace

Okay, this is good. Please also run `make run-test TEST=gc/epsilon` explicitly; it is supposed to run in tier1 already, but better be safe than sorry.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1794