[jdk21] RFR: 8310743: assert(reserved_rgn != nullptr) failed: Add committed region, No reserved region found

[Albert Mingkun Yang]

On Mon, 3 Jul 2023 14:24:05 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> Backport of JDK-8310743
> 
>> 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.
> 
> This pull request contains a backport of commit [f393975](https://github.com/openjdk/jdk/commit/f393975d1b9423835a7aa42f6ffc0656499701d7) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.
> With merge conflict in `src/hotspot/share/gc/z/zPhysicalMemory.cpp` (header includes) resolved.

Marked as reviewed by ayang (Reviewer).

-------------

PR Review: https://git.openjdk.org/jdk21/pull/92#pullrequestreview-1511696733