RFR: 8312132: Add tracking of multiple address spaces in NMT [v74]

[Thomas Stuefe]

On Fri, 10 May 2024 11:41:05 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Some style
>
> src/hotspot/share/nmt/vmatree.cpp line 2:
> 
>> 1: /*
>> 2:  * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
> 
> Be a dear and add us, please :-)

Though by this time, you spent more time on the VMATree then I originally did. Still ..

> src/hotspot/share/nmt/vmatree.hpp line 151:
> 
>> 149: 
>> 150:   SummaryDiff release_mapping(position from, position sz) {
>> 151:     Metadata empty;
> 
> Just a nit, but instead of the Metadata::Metadata() ctor creating an empty object, could we possibly scrap the default ctor and have an explicit static constexpr Metadata empty with invalid stackindex and mtNone as ctor args? I find that nicer to read.

Oh, another thing, maybe rename this to something else. `Metadata` has a clear meaning in hotspot. Maybe something like RegionData?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18289#discussion_r1596677600
PR Review Comment: https://git.openjdk.org/jdk/pull/18289#discussion_r1596676673