[turbopack] Unify Cell Storage#92974
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lukesandberg merged 9 commits intocanaryfrom Apr 21, 2026
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Add new serializability options. The key thing we want to distinguish is 'this cell is not serializable and it is important' vs this cell isn't _worth_ serializing Currently there isn't a reason to distinguish, but with eviction there is. In theory we should implement a priority system * unevictable (e.g. DiskFileSystemInner). not serialiable fundamentally, evicting this breaks the watcher * expensive (e.g. the WorkerThreadPool). not serializable fundamentally, evicting this would be a perf hit * cheaply derivable: (e.g. EcmascriptChunkItemContent). serializable, but not worth it * regular: everthing else But for now there are just two levels unevictable and everything else, if some of the 'everything else' isn't serializable that is fine.
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lukesandberg
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Apr 18, 2026
lukesandberg
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Apr 18, 2026
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lukesandberg
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Apr 18, 2026
sokra
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Apr 19, 2026
lukesandberg
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Apr 19, 2026
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Discussed with nicholas lets split this into 2 keys serialization="auto,hash,custom,none" this will be a bit more intuitive but it does introduce the issue of having some 'meaningless combinations' for now we can just ban unsupported combinations |
sokra
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Apr 21, 2026
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What
Tightens the value-type persistence API and sets the table for a future eviction policy. Two user-visible changes on the
#[turbo_tasks::value(...)]macro:serialization = "none"→serialization = "skip"— imperative ("skip persisting") instead of descriptive. Making it clear that it isn't that we are missing a feature but rather that we are choosing to not persist (of course persisting might be impossible but that is generally rare)evict = "always" | "last" | "never"attribute — replaces the old overloaded"none"semantic. Only valid withserialization = "skip". Defaults to"always".Internally this collapses
persistent_cell_data+transient_cell_datainto onecell_datamap and replaces the oldbincode: Option<(enc, dec)>field with a four-variantValueTypePersistenceenum. Eviction machinery itself is a follow-up PR; this PR just gives each value type a precise, queryable persistence/eviction descriptor.Why break out a new parameter?
serialization = "none"on canary conflated three different intents:Ropes) — fine to evict, recompute is cheap.State<>cells,Arc<Mutex<_>>dedup histories) — can't be recomputed without losing accumulated mutations.They all produced identical runtime behavior (stored in transient_cell_data), so eviction can't tell them apart. The fix is two orthogonal attributes:
The macro rejects
evicton any otherserializationmode.ValueTypePersistenceenumReplaces
ValueType.bincode: Option<(enc, dec)>:The existing
"hash"mode gets its ownHashOnlyvariant rather than being folded intoSkipPersist, which lets the backend gate its hash-writing and hash-comparison paths precisely.Unified
cell_datastoragepersistent_cell_data: AutoMap<CellId, TypedSharedReference>+transient_cell_data: AutoMap<CellId, SharedReference>collapse intocell_data: CellData.CellDatais a newtype overAutoMap<CellId, SharedReference>with a custom bincode impl that filters non-Persistableentries at encode time. This removes theis_serializable_cell_content: boolparameter that was threading through ~14 read/write call sites.Uses
SharedReferenceinstead ofTypedSharedReference—CellIdalready carries theValueTypeId.Annotation sweep
All prior
serialization = "none"sites move to eitherserialization = "skip", evict = "never"orserialization = "skip", evict = "last"based on a per-site audit. Summary:evict = "last"(6 sites) — re-derivable but expensive:SwcPluginModule,EvaluatePool,ChildProcessPool,WorkerThreadPool,EffectInstance,Effectsevict = "never"(2 sites) — interior-mutable state accumulated across the session:ConsoleUi(Arc<Mutex<SeenIssues>>),VersionState(State<VersionRef>with HMR invalidators)The distinguishing rule:
evict = "never"only when the value holds interior mutability accumulated across the session. Everything else can be re-derived (possibly expensively) by re-running the producing task.Follow-ups (separate PRs)
ValueTypePersistence— respectsSessionStateful(never evict), prefers cheapSkipPersistoverexpensive: trueones. Either as part of Proof of concept: task eviction after snapshot for turbo-tasks-backend #91790 or afterwards depending on when things land