Custom Memory Allocators (Pool, Arena, Stack) for High-Frequency Game Loops: Edge Cases, Failure Modes, and Root-Cause Debugging

[Lucas Carter]

I’ve been rebuilding our per-frame allocator for the sim and got stuck on a real edge case with the pool allocator. We’re seeing periodic 16ms hitches that correlate with pool exhaustion, but the hitches don’t show up under valgrind or even with AddressSanitizer. Anyone hit this before? When a pool request fails and you fall back to the system allocator mid-frame, does that single malloc/free pair actually blow your frame budget, or is the allocator itself the problem masking the symptom?

For the arena allocator, what’s your strategy when a frame needs a buffer that exceeds the pre-allocated region? I’ve seen people just bail and use a bump-only fallback, but that defeats the whole point. Also, how are you handling nested scopes with stack allocators—do you use refcounting or explicit save/restore of the cursor pointer? And one thing nobody talks about: how do you track down a use-after-free when there’s no heap to probe and everything lives in a fixed region? Any debugging tricks or tools that actually work in zero-allocation frames?

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[Chloe Ramirez]

Great topic. The failure mode I see most often is conflating the failure modes of each allocator—the bugs aren’t interchangeable. For pool allocators, the classic footgun is the overflow path: when the free list exhausts, you either abort, fall back to a slow path, or silently overflow into adjacent blocks (the worst, because it corrupts heap metadata and the crash shows up frames later, miles from the actual allocation). Always make the overflow path deterministic and instrumented so you can tell when a pool ran dry rather than discovering it via a random segfault. Alignment is the second trap—pool blocks are usually sized to a fixed stride, but if you’re storing types with

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