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Jetsam-proof stem separation: headroom gates and playback-start hold - #86
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sanylax0 merged 1 commit intoJul 18, 2026
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RCA identified the ORT session load (~600 MB transient) plus the first HT-Demucs window's attention arena (up to ~1.7 GB) as the app's largest allocation, landing exactly when playback, UI, and (first run) the model download are also ramping — a per-process-limit kill on devices with a tight cap. Three structural guards: - Hard start gate: a separation may not begin unless os_proc_available_memory headroom exceeds a required budget (1400 MB to start; tune from mem[] breadcrumbs). Deferred work retries on later ensureStems passes. - Per-window floor: abort before the next window if headroom falls under 600 MB, via the existing abort/cleanup path. - Playback-start hold: the session's first stem demand arms a 60 s hold so the peak never stacks on engine/UI ramp-up; one scheduled retry re-drives ensureStems after the hold.
sanylax0
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Jul 18, 2026
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What
PR 2 of the jetsam RCA plan — makes the leading kill scenario structurally impossible instead of hoping mitigations fit under the (possibly iOS-26-tightened) per-process cap.
The RCA sized the stem-separation peak at: ~330 MB fp32-upcast weights + ~300 MB protobuf load transient + up to ~1.7 GB first-window attention arena — landing exactly when playback, UI, and (first run) the silent 158 MB model download are also ramping. The merged arena shrinkage only frees memory after a run, so it cannot cap the first-window peak.
How
Three guards, all reusing existing plumbing:
PreparationQueue+Stems.separateStems): after acquiring the separation slot, the task checksos_proc_available_memoryheadroom againstStemSeparationBudget.requiredStartMB(1400 MB initial value — tune from themem[]breadcrumbs of the diagnosis run) and defers cleanly (slot released, in-flight key removed, session freed if idle) when short. Deferred tracks retry on every subsequentensureStemspass.StemSeparator.ortInference): abort before the next window if headroom drops under 600 MB — proactive version of the existing memory-warning abort, using the same partial-stems cleanup path.ensureStems): the session's first stem demand arms a 60 s hold; separations are skipped during it and one scheduled retry re-drivesensureStemsafter the hold, so the ORT peak never stacks on engine/UI/download ramp-up and stems still arrive mid-song.MemoryFootprintgains a reusableheadroomMBaccessor.Testing
On device (after merging with #85's diagnostics): fresh launch → play an un-separated track → the console should show either the hold ("no separation in the first minute") followed by a normal separation, or a
deferring separation … MB headroomnotice — and no kill. Note: if the diagnosis run shows the real cap is lower than assumed, adjustStemSeparationBudget.requiredStartMBaccordingly.🤖 Generated with Claude Code
https://claude.ai/code/session_013TJoWkqg8bzkGdzxWhWjWP
Generated by Claude Code