RFR: 8280088: NMT: Make mtGCCardSet the subcategory of mtGC

[Thomas Stuefe]

On Mon, 17 Jan 2022 18:11:17 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> [JDK-8017163](https://bugs.openjdk.java.net/browse/JDK-8017163) introduced a new category, `mtGCCardSet` in NMT tracking. This makes logging look rather weird, and technically miscounts the space taken by GC-specific data structures, if you are accustomed to look at "GC" only:
> 
> 
> - GC (reserved=142426KB, committed=142426KB)
>                             (malloc=89554KB #3658)
>                             (mmap: reserved=52872KB, committed=52872KB)
>  
> - GCCardSet (reserved=128KB, committed=128KB)
>                             (malloc=128KB #1539)
> 
> 
> We can instead recast it as the subcategory of `mtGC`. It would be similar to `mtThreadStacks` that are accounted separately, but reported as part of `mtThread`.
> 
> 
> - GC (reserved=142584KB, committed=142584KB)
>                             (card sets: 128KB)
>                             (malloc=89583KB #3780)
>                             (mmap: reserved=52872KB, committed=52872KB) 
> 
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug `runtime/NMT`
>  - [ ] Linux x86_64 fastdebug `tier1`

I created https://bugs.openjdk.java.net/browse/JDK-8281819 to track the proposed NMT category grouping

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PR: https://git.openjdk.java.net/jdk/pull/7115