Off-heap memory leak

I'm experiencing an off-heap memory leak, quickly consuming my PC's RAM over minutes of creative-mode exploration.

The Java heap is otherwise behaving fine and appears to respect the assigned limit (4GB).  The memory consumption is associated with the java process.

• Minecraft:  1.18 Pre-release 1, 21w44a
• Launcher:  MultiMC 5 0.6.13-2519
• Java:  OpenJDK 16.0.1+9-Ubuntu-120.04
• OS:  Ubuntu 20.04.3
• RAM:  16GB (system) with a 4GB Java heap allocation
• GPU:  NVIDIA GeForce GTX 1070
• GPU Driver:  3.2.0 NVIDIA 495.44 (nvidia-driver-495)

I'll be digging deeper into the issue but I'm unfamiliar with Java, so any tips on tracking down the source of the leak would be helpful!