RFR: 8329203: Parallel: Investigate Mark-Compact for Full GC to decrease memory usage [v4]

[Guoxiong Li]

On Wed, 15 May 2024 20:50:24 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> src/hotspot/share/gc/parallel/psParallelCompact.cpp line 2085:
>> 
>>> 2083: 
>>> 2084:   // end_addr is inclusive to handle regions starting with dead space.
>>> 2085:   while (cur_addr <= end_addr) {
>> 
>> When the `cur_addr` is equal than `end_addr`, the corresponding region would be handled by another thread. Why does this thread need to handle it? Do I miss anything?
>
> This and the following question are closely related. The troublesome scenario is that the region for a worker starts with dead-space, which is continuation from proceeding region. In this case, we wanna the proceeding worker creates a single large filler that spans over to regions belong to next worker.

Ohh, I know what it means now. We need to creates a single large filler when the dead-space is **across regions**. But the next worker don't know whether the start dead space had been handled by its previous worker or not, so we always handle the start dead space in its previous worker to avoid such hard judgement. Thanks for your explanation.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19101#discussion_r1603374531