RFR(M):8252103:parallel heap inspection for ParallelScavengeHeap(Internet mail)

[linzang(臧琳)]

Dear All,
     I create a PR at https://github.com/openjdk/jdk/pull/25.
     Would you like to help review ? Thanks!
 
BRs,
Lin

>    Hi David,
>         My mistake, it should be 2x faster with this patch, Thanks for point it out!
>          Raw data of Jmap histo (Average of 5 times run)
>          Before: 685ms
>          After(4threads): 356ms
>
>    BRs,
>    Lin
>
>    > On Sep 1, 2020, at 12:45 PM, David Holmes <david.holmes at oracle.com> wrote:
>   > 
>    > Hi Lin,
>    > 
>    >> On 1/09/2020 12:28 pm, linzang(臧琳) wrote:
>    >> Dear All,
>    >>         May I ask your help to review this change of adding parallel
>    >> heap inspection for PSS Heap?
>    >>         bug:   https://bugs.openjdk.java.net/browse/JDK-8252103
>    >>         webrev:
>    >> http://cr.openjdk.java.net/~lzang/jmap-8214535/8252103/webrev.00/
>    >>         My preliminary measurement shows about ~1x speed up for when
>    >> using 4 threads of jmap -histo. (on a 4 core Linux machine, with -xmx8g
>    >> and objects takes 1.5GB in heap.)
>    > 
>    > ~1x speed up is not a speed up. What exactly did you mean here?
>    > 
>    > Thanks,
>    > David
>    > -----
>    > 
>    >>         As spaces in youngGen of parallelScvangeHeap is hard to be
>    >> divided for parallel iteration, this change just assign different worker
>    >> thread to process different space in youngGen, that is, 1 thread to
>    >> process whole eden space etc. so this may be one reason that speedup is
>    >> not scale with parallel thread number.
>    >> BRs,
>    >> Lin
>    >