RFR: Borrow from old gen [v2]

[William Kemper]

On Mon, 7 Feb 2022 23:33:41 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahThreadLocalData.hpp line 176:
>> 
>>> 174:   }
>>> 175: 
>>> 176:   static void disable_plab_promotions(Thread* thread) {
>> 
>> This looks wrong - shouldn't it set `_plab_allows_promotion` to false here? It's also not clear to me how this relates to the other changes here. When would we disable plab promotion?
>
> Good catch.  I got careless with copy and paste.  Thanks.

I didn't see where this is called. Is the used? Why would we disable plab promotion?

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PR: https://git.openjdk.java.net/shenandoah/pull/110