RFR: 8331539: [REDO] NMT: add/make a mandatory MEMFLAGS argument to family of os::reserve/commit/uncommit memory API [v2]

[Afshin Zafari]

On Thu, 23 May 2024 13:04:24 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fixed the missing parts of shenandoahHeap.cpp
>
> src/hotspot/share/nmt/virtualMemoryTracker.cpp line 506:
> 
>> 504:       return true;
>> 505:     assert(reserved_rgn->end() == rgn.end() || reserved_rgn->base() == rgn.base(), "extra memory should be at either end of the region.");
>> 506:   }
> 
> This seems like an extreme hack. I understand that this just follows the tradition of the rest of the hacks in this file, but can't this be better handled in the CDS layer above?

TBH, I don't like it too. Unfortunately, chopping extra memory is done at `os:xxx` layer and reporting the case back to CDS would need to pass all the chopping info up to CDS. In addition, it is valid in CDS that a region is partitioned into sub regions and releasing sub regions can be silently and correctly ignored.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19343#discussion_r1613202175