RFR: 8313593: Generational ZGC: NMT assert when the heap fails to expand

[Thomas Schatzl]

On Wed, 2 Aug 2023 07:15:31 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> The following assert is hit when the ZGC fails to commit more memory for the heap:
> 
> assert(size > 0) failed: Invalid size
> ...
> V  [libjvm.so+0x185d157]  VirtualMemoryTracker::add_committed_region(unsigned char*, unsigned long, NativeCallStack const&)+0x4d7  (virtualMemoryTracker.cpp:428)
> V  [libjvm.so+0x19c1f33]  ZNMT::process_fake_mapping(zoffset, unsigned long, bool)+0xa3  (memTracker.hpp:168)
> V  [libjvm.so+0x19db817]  ZPhysicalMemoryManager::commit(ZPhysicalMemory&)+0x47  (zPhysicalMemory.cpp:312)
> V  [libjvm.so+0x19d1e4b]  ZPageAllocator::alloc_page_finalize(ZPageAllocation*)+0x6b  (zPageAllocator.cpp:427)
> 
> The problem is that we still call the NMT reporting code even when the committed size is zero.

Marked as reviewed by tschatzl (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/15120#pullrequestreview-1558434192