Unexpected heap growth on Linux/x86_64 with VERY_SMALL_CONFIG

[ivmai]

Source: master (8311518)
Build: https://app.travis-ci.com/github/ivmai/bdwgc/jobs/627052032
Host: Ubuntu Jammy / x86_64
Config: CONF_OPTIONS="--enable-cplusplus --enable-gc-assertions --enable-static" CFLAGS_EXTRA="-D VERY_SMALL_CONFIG"
Output (gctest):

Supported VDBs: manual soft mprotect
Switched to incremental mode
Reading dirty bits from /proc
Completed 6 tests (concurrently)
Allocated 1498375 collectable objects
Allocated 1218 uncollectable objects
Allocated 718278 atomic objects
Reallocated 36 objects
Garbage collection after fork is tested too
Finalized 1657/1657 objects - finalization is probably OK
Total number of bytes allocated is 580570528
Total memory use by allocated blocks is 442368 bytes
Final heap size is 442368 bytes
Unexpected heap growth - collector may be broken (heapsize: 58531840, expected: 41943040)

Probably related: #639, #595, #538