After many long years, the Memory64 proposal for WebAssembly has finally been released in both Firefox 134 and Chrome 133. In short, this proposal add

Is Memory64 actually worth using? | SpiderMonkey JavaScript/WebAssembly Engine

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2025-01-16 03:00:05

After many long years, the Memory64 proposal for WebAssembly has finally been released in both Firefox 134 and Chrome 133. In short, this proposal adds 64-bit pointers to WebAssembly.

If you are like most readers, you may be wondering: “Why wasn’t WebAssembly 64-bit to begin with?” Yes, it’s the year 2025 and WebAssembly has only just added 64-bit pointers. Why did it take so long, when 64-bit devices are the majority and 8GB of RAM is considered the bare minimum?

It’s easy to think that 64-bit WebAssembly would run better on 64-bit hardware, but unfortunately that’s simply not the case. WebAssembly apps tend to run slower in 64-bit mode than they do in 32-bit mode. This performance penalty depends on the workload, but it can range from just 10% to over 100%—a 2x slowdown just from changing your pointer size.

This is not simply due to a lack of optimization. Instead, the performance of Memory64 is restricted by hardware, operating systems, and the design of WebAssembly itself.