Chunk 30.1

In this chunk, the user rejected the assistant's previous ad-hoc fix of capping the pinned pool at 40% of the budget, correctly pointing out it was unprincipled and would catastrophically harm performance on memory-constrained systems where pinned memory is the dominant operational memory. The user insisted that the pinned pool and memory manager must be properly integrated to collaborate on memory management, avoiding thrashing while maximizing parallelism. This prompted the assistant to abandon the quick cap and undertake a deep architectural analysis of the memory budget system. The assistant traced the root cause to the fundamental accounting mismatch: the pinned pool's `cudaHostAlloc` buffers are invisible to the `MemoryBudget`. When a partition completes, its per-partition budget reservation is released, but the pool retains the physical pinned memory. This blind spot causes the budget to systematically over-commit, eventually triggering the cgroup OOM killer. The assistant explored several principled solutions—including routing all pool allocations through the budget, splitting per-partition reservations into pinned and heap components, and having the pool hold a permanent budget reservation—carefully analyzing how to avoid the double-counting that plagued a previous attempt. The assistant settled on a two-phase reservation model: the pool acquires budget when allocating new buffers, and when a partition successfully checks out pinned buffers, it reduces its own per-partition reservation by the buffer size (since the pool's budget already covers that memory). To confirm the exact mechanics, the assistant read the full `memory.rs` file, gaining a complete understanding of the RAII `MemoryReservation` guards, the permanent vs. working memory split, and how per-partition reservations are calculated. With this comprehensive understanding, the assistant is now prepared to implement the proper budget-aware pinned pool integration, ensuring the system dynamically adapts to available memory without arbitrary caps.

The Principled Pivot: From Ad-Hoc Cap to Budget-Aware Memory Management 4365 words

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