RFR (XS) 8222818: NMT summary could show the GC in use

[Zhengyu Gu]

On 4/22/19 8:19 PM, David Holmes wrote:
> Hi Eric,
> 
> On 23/04/2019 8:13 am, Eric Caspole wrote:
>> Hi, could I have reviews and any opinions on this little change to 
>> show the GC name in the NMT output, as this helps us to more easily 
>> triage performance data.
> 
> The idea seems fine.

> 
> For the implementation wouldn't it be simpler to do something like:
> 
> if (flag == mtGC) {
>    out->print("%s - %s (", NMTUtil::flag_to_name(flag),
>                            GCConfig::hs_err_name());
> } else {
>    out->print("-%26s (", NMTUtil::flag_to_name(flag));
> }
> 
Yes, this is simpler.

I don't like where the name is placed, it screws up section alignments. 
I would prefer to place name inside parenthesis. e.g.

- GC (g1 gc reserved=379056KB, committed=93220KB)

Thanks,

-Zhengyu

> and skip the need for a local buffer and snprintf?
> 
> Aside: it's probably used in enough different contexts that 
> GCConfig::hs_err_name should be renamed.
> 
> Also if the VM terminates during initialization is it possible for this 
> code to be executed before the GCConfig has been setup? And if so how 
> will it behave?
> 
> Thanks,
> David
> 
>> This passed tier 1 and 2.
>> Thanks,
>> Eric
>>
>>
>> JBS:
>> https://bugs.openjdk.java.net/browse/JDK-8222818
>>
>> webrev:
>> http://cr.openjdk.java.net/~ecaspole/JDK-8222818/02/webrev/