turbopack: reduce EffectStateStorage memory by storing u128 content hashes#92902
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turbopack: reduce EffectStateStorage memory by storing u128 content hashes#92902
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…l content Reduces memory usage in EffectStateStorage by storing a xxh3 128-bit hash of the effect value instead of the full ReadRef<PersistedFileContent> or ReadRef<LinkContent>. The hash is precomputed at effect construction time. Co-Authored-By: Claude <noreply@anthropic.com>
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Apr 16, 2026
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What?
In
turbo-tasks-fs, theWriteEffectandWriteLinkEffectstructs now store a precomputedu128xxh3 content hash instead of returning the fullReadRef<PersistedFileContent>/ReadRef<LinkContent>from theirEffect::value()implementations.The associated type
Effect::Valueis changed fromReadRef<PersistedFileContent>/ReadRef<LinkContent>tou128for both effect types.LinkContentgains aDeterministicHashderive to support hashing viahash_xxh3_hash128.Why?
EffectStateStoragestores the last-applied value for each effect key inlast_applied: Mutex<Option<Box<dyn Any + Send + Sync>>>to enable a double-checked deduplication fast path (skip re-writing a file if content hasn't changed). In long-running sessions this map grows continuously and holds onto a lot of memory because it stores full file content (ReadRef<PersistedFileContent>) or full link content (ReadRef<LinkContent>) for every file ever written.Storing a
u128hash (16 bytes) instead of the full content significantly reduces memory usage while preserving the deduplication semantics (hash equality implies content equality with negligible collision probability).How?
content_hash: u128field toWriteEffectandWriteLinkEffect, computed at construction time usinghash_xxh3_hash128(xxh3 128-bit non-cryptographic hash, already used elsewhere in turbopack for content addressing).Effect::Value = u128for both effect types;value()returns&self.content_hash.EffectStateStoragenow storesBox<u128>(24 bytes on the heap) per entry instead ofBox<ReadRef<...>>which held a reference-counted pointer into potentially large file content.EffectStateStorage,Effects::apply(), orDynEffectvtable — the existingAny/DynPartialEqmachinery works transparently withu128.