RFR (T) 8243393: Improve ReservedSpace constructor resolution

[coleen.phillimore at oracle.com]

I already checked this in because it was trivial.

On 4/28/20 11:53 PM, David Holmes wrote:
> Hi Coleen,
>
> On 28/04/2020 2:12 am, coleen.phillimore at oracle.com wrote:
>> Summary: Remove possibly ambiguous constructor and use directly in 
>> ReservedCodeHeap
>>
>> Tested with tier1-3.
>>
>> open webrev at 
>> http://cr.openjdk.java.net/~coleenp/2020/8243393.01/webrev
>> bug link https://bugs.openjdk.java.net/browse/JDK-8243393
>
> Sorry but I don't understand the mapping to the constructors. In this 
> original call from cardTable.cpp:
>
> ReservedSpace heap_rs(_byte_map_size, rs_align, false);
>
> this calls the 4-arg constructor as-if:
>
> ReservedSpace heap_rs(_byte_map_size, rs_align, false, NULL);
>
> and rs_align maps to the alignment parameter.
>
> But in the new two-arg constructor call:
>
> ReservedSpace heap_rs(_byte_map_size, rs_align)
>
> the rs_align is no longer treated as alignment but rather 
> preferred_page_size! It isn't at all obvious to me that this is an 
> equivalent construction.
>
http://cr.openjdk.java.net/~coleenp/2020/8243393.01/webrev/src/hotspot/share/gc/shared/cardTable.cpp.udiff.html

Yes, you're right, this is part of the change is wrong.  It was matching 
the version I took out.  I'll file a bug to fix it.

> Both constructors need to be adequately documented - at present only 
> the two-arg constructor is.

Please suggest a comment.

thanks,
Coleen
>
> Thanks,
> David
> http://cr.openjdk.java.net/~coleenp/2020/8243393.01/webrev/src/hotspot/share/gc/shared/cardTable.cpp.udiff.html 
>
>> Thanks,
>> Coleen