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WebAssembly Allocator Benchmarks

Performance Benchmark

Run with just wasm-perf. Source code can be found in wasm-perf/.

wasm random actions benchmark plot

Size Benchmark

Run withjust wasm-size. Source code can be found in wasm-size/.

wasm size benchmark plot

Conclusions

  • If all you care about is WebAssembly module size, use lol_alloc

  • If all you care about is performance, use Talc

  • If you want a "best of both worlds" then use Talc (consider setting "disable-realloc-in-place" or "disable-grow-in-place"), or RLSF's SmallGlobalTlsf.

  • DLmalloc and RLSF's GlobalTlsf are worse in both size and performance to Talc.

Caveats

Talc's default WebAssembly configuration is less memory-efficient compared to the alternatives. The defaults are chosen as WebAssembly modules rarely push the limits of system memory, whereas network bandwidth and runtime performance dictate the latency end-users experience, and therefore is often crucial.

Expect a 10%-15% higher runtime memory usage, though I've only taken rough measurements. Your mileage may vary. To test for yourself, you can use core::arch::wasm32::memory_size::<0>() to see how much memory the WebAssembly module is using.

Talc's memory efficiency is almost entirely dependent on the Binning configuration used. You can swap out WasmBinning if desirable.

Using WasmGrowAndExtend instead of WasmGrowAndClaim will also help.

WasmGrowAndExtend vs. WasmGrowAndClaim

By default, Talc claims new WebAssembly pages on demand using the WasmGrowAndClaim OOM handler.

An alternative to consider is WasmGrowAndExtend:

  • Extends the heap instead of claiming new heaps. This reduces memory fragmentation and thus may improve memory efficiency somewhat.
  • Requires ~250 more bytes of WebAssembly module size due to pulling in the Talc::extend code.
use talc::{wasm::*, cell::TalcSyncCell};

#[cfg(all(not(target_feature = "atomics"), target_family = "wasm"))]
#[global_allocator]
static TALC: TalcSyncCell<WasmGrowAndExtend, WasmBinning> = TalcSyncCell::new_wasm(WasmGrowAndExtend::new());