Reduce per-connection memory overhead#414
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9seconds merged 2 commits into9seconds:masterfrom Mar 29, 2026
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- Use sync.Pool for relay buffers instead of stack-allocated arrays. A [16379]byte on the goroutine stack forces Go to grow it to 32KB (next power of two). Pooled buffers keep goroutine stacks small. - Same fix for doppelganger write buffer ([16384]byte in conn.start). - Replace idle goroutines with context.AfterFunc in proxy.ServeConn and relay.Relay. These goroutines existed only to wait on ctx.Done() and close connections. AfterFunc achieves the same without allocating a goroutine until the context is actually cancelled. Net effect: at 3000 concurrent connections on a 1-vCPU/961MB VPS, the unmodified binary drops 246 connections and falls to 10 MB/s. With these changes: zero failures, 63 MB/s, 31% lower RSS. Closes 9seconds#412
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Summary
var buf [16379]byteon the goroutine stack forces Go runtime to grow it to 32 KB (next power of two). Pooled buffers keep stacks small (~2-4 KB).[16384]byteinconn.start().proxy.ServeConnandrelay.Relaythat existed only to<-ctx.Done()and close connections.Benchmark (VPS, 1 vCPU, 961 MB RAM, real mtg binary, domain fronting to echo)
At moderate concurrency (~1000) the difference is within noise. At 3000 connections the unmodified binary breaks down: 246 connection timeouts, throughput drops to 10 MB/s. With this change: zero failures, 63 MB/s, 31% lower RSS.
Test plan
go test ./...passesCloses #412