RFR: JDK-8318636: Add jcmd to print annotated process memory map

[Zhengyu Gu]

On Mon, 23 Oct 2023 05:25:50 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> > The hs_err file includes a dump of the maps file. It seems these annotations would be useful there also.
> 
> I thought about this too. The problem is the printing may take long since it is O^2 (iterate through VMAs, for each one iterate NMT regions). We had cases where the process ran with >20 mio VMAs (ZGC with a 5TB heap).
> 
> But thinking further, this is a problem anyway, since the hs-err file was >2GB. And we do have per-step timeouts in the hs-err writer. So, stopping after a set number of VMAs (lets say 100k, that covers 99% of all processes) and otherwise relying on the hs-err timeout code may be ok.
> 
> I'll give it a shot.

IIRC, both lists are sorted, should be a way to reduce time complexity.

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PR Comment: https://git.openjdk.org/jdk/pull/16301#issuecomment-1775748234