Shared::mappings only ever grew: clear_cache reset sent_keys and told the
worker to drop its fd cache, but nothing closed the host-side CUDA IPC
mappings for the previous pool generation. A session that renegotiates
repeatedly (mode changes, HDR toggles, client reconnects) accumulated a
pool's worth of stale mappings each time, each pinning a host VA
reservation to peer memory the worker had already freed.
Mappings now carry a refcount and a retired flag. clear_cache closes every
unreferenced mapping immediately and marks the rest retired; a retired
mapping closes when its last in-flight DeviceBuffer releases. The worker's
half of the contract: ClearCache also forgets its VA→id map, so anything
delivered after the boundary gets a fresh id WITH its descriptor — without
that, a same-shape renegotiation (worker keeps its pool) would re-deliver
an old id whose host mapping was just closed, and the host would misread
it as a desync. Ids never repeat (next_id only counts up), so fresh ids
cannot collide with the graveyard.
(R6 from design/pf-zerocopy-sweep-handoff.md.)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
enricobuehlerandClaude Fable 5
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