In this lesson, you will learn how to calculate and monitor memory budgets for Nanite assets to ensure your high-fidelity geometry doesn't cause texture or geometry thrashing during runtime.
Understanding the Nanite Budget
When working with Nanite, you aren’t dealing with traditional draw calls in the same way as standard meshes; instead, you are managing a streaming system that pulls clusters of geometry into memory based on view-dependent importance. "Thrashing" occurs when the demand for new geometry clusters exceeds the available memory bandwidth or heap space, forcing the engine to constantly evict and re-load data, leading to micro-stutters and visible pop-in.
Calculating the Memory Footprint
To evaluate your budget, you must distinguish between on-disk size and resident memory. Because Nanite uses a compressed, tiled format, you can monitor the actual memory footprint using the console command r.Nanite.Streaming.StreamingPoolSize.
When defining a budget for your target hardware (e.g., PS5 vs. mid-range PC), consider these three variables:
- Resident Clusters: The number of clusters currently in VRAM.
- Streaming IO Throughput: How fast the storage can feed the Nanite streaming pool.
- Overdraw/Density: Even with Nanite, excessive triangle density on screen increases the cost of the programmable rasterizer and G-Buffer passes.
Monitoring with Stats
You should frequently check your memory usage during play-in-editor or on-device testing using:
stat nanite
This command provides a breakdown of Visible Cluster Count and Streaming Pool Memory. If the Pool Memory reaches its limit, the engine will throttle incoming geometry. If you notice the "Streaming Pool" limit is consistently reached, you have two choices: either increase the r.Nanite.Streaming.StreamingPoolSize (if hardware allows) or simplify the source assets to reduce the persistent footprint of the scene.
When deploying high-fidelity assets, always cross-reference your total Nanite footprint with your G-Buffer storage requirements. If your assets are too dense, the increased memory pressure will force the virtualized geometry system to work against your deferred rendering pipeline, causing the very performance degradation you are trying to avoid.
Key Takeaway: Monitor the stat nanite output to ensure your resident geometry clusters fit within your allocated streaming pool, preventing I/O thrashing and maintaining consistent frame delivery.