On Mon, 10 Jul 2023 11:06:23 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
>> Thomas Stuefe has updated the pull request incrementally with two additional
>> commits since the last revision:
>>
>> - Add test with 1ms trim interval
>> - No need for atomics
>
> src/hotspot/share/runtime/trimNativeHeap.cpp line 106:
>
>> 104: ml.wait(wait_ms);
>> 105: } else if (at_or_nearing_safepoint()) {
>> 106: ml.wait(safepoint_poll_ms);
>
> OK, so here is a little problem. Suppose I want to run trims very often, like
> every 10ms. This loop would stall for 250ms when safepoint is detected, which
> throws off this guarantee. Can we instead go and sleep for
> `TrimNativeHeapInterval`? AFAICs, this plays nicely with heuristic guidance
> (short intervals -> more interference), and it would best-effort stall for
> twice the interval when safepoint interjects.
But then we have a problem for larger trim intervals. Loosing one or multiple
trim attempts because a safepoint happened to happen hurts if the interval is
e.g. 5 minutes.
We could either wait for `MIN2(TrimNativeHeapInterval, safepoint_poll_ms)`.
Or, at the cost of one Mutex grab per safepoint, I could do a `notify_all()` at
the end of a safepoint.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/14781#discussion_r1258176657
