RFR: 8310743: assert(reserved_rgn != nullptr) failed: Add committed region, No reserved region found

[Albert Mingkun Yang]

On Fri, 30 Jun 2023 13:07:17 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> JDK-8309675 tried to solve the issue of NMT reporting to much committed memory by faking the virtual addresses registered when committing physical memory. This mapping was simply the `virtual address  = physical offset in backing file + heap base`. This works when ZGC gets a contiguous heap which starts at the heap base. However fails if it does not start at the heap base or is discontiguous.
> 
> This proposal fixes this by keeping track of all the reserved virtual address ranges and by creating a mapping from the physical offsets to the actual reserved virtual address ranges. If the physical offsets committed maps to multiple reserved ranges, it is processed as multiple commits.
> 
> The develop flag `ZForceDiscontiguousHeapReservations` is introduced to test the discontiguous heap feature and interactions.
> 
> Testing: 
>  * Added test on all Oracle platforms
>  * GHA
>  * Running tier1-3

I think it's better to fail-early when sth unexpected occurs, so both places warrant a should-not-reach-here; subjective though.

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Marked as reviewed by ayang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14730#pullrequestreview-1511192170