nottinygc

nottinygc requires TinyGo 0.28+

nottinygc is a replacement memory allocator for TinyGo targetting WASI. The default allocator is built for small code size which can cause performance issues in higher-scale use cases. nottinygc replaces it with bdwgc for garbage collection and mimalloc for standard malloc-based allocation. These mature libraries can dramatically improve the performance of TinyGo WASI applications at the expense of several hundred KB of additional code footprint.

Note that this library currently only works when the scheduler is disabled.

Usage

Using the library requires both importing it and modifying flags when invoking TinyGo.

Add a blank import to the library to your code's main package.

import _ "github.com/wasilibs/nottinygc"

Additionally, add -gc=custom and -tags=custommalloc to your TinyGo build flags.

tinygo build -o main.wasm -gc=custom -tags=custommalloc -target=wasi -scheduler=none main.go

Using with Envoy

This library relies on WASI to implement certain functionality. Envoy's support for WASI is currently not complete so the library will not load in an application on Envoy as is. Notably, the sched_yield function is not implemented, which is used by mimalloc when returning memory to the OS. Because memory cannot be returned to the OS with Wasm, it is fine to stub this with a no-op as a workaround, which can be done with the following code anywhere in your application.

//export sched_yield
func sched_yield() int32 {
	return 0
}

Other hosts that implement WASI fully, such as wazero, will not have this issue.

Performance

Benchmarks are run against every commit in the bench workflow. GitHub action runners are highly virtualized and do not have stable performance across runs, but the relative numbers within a run should still be somewhat, though not precisely, informative.

One run looks like this

BenchmarkGC/bench.wasm-2         	      52	 220294559 ns/op
BenchmarkGC/benchref.wasm-2      	       6	2000167805 ns/op

The benchmark is very simple, allocating some large strings in a loop. We see nottinygc perform almost 10x better in this benchmark. Note that just allocation / collection time is not the only aspect of GC performance, allocation locality and fragmentation can also affect performance of real-world applications. We have found that the default allocator can cause applications to run out of memory, possibly due to fragmentation, whereas this library will continue to run indefinitely.