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AssemblyScript / assemblyscript

A TypeScript-like language for WebAssembly.
https://www.assemblyscript.org
Apache License 2.0
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feat: `lowMemoryLimit` can accept more than 1 page value #2857

Open HerrCai0907 opened 2 weeks ago

HerrCai0907 commented 2 weeks ago

The original lowMemoryLimit only support memory less than 64kB (1 wasm page). This PR wants to extend the function of lowMemoryLimit to support more than 64kB memory limitation.

CountBleck commented 2 weeks ago

What's the use case for this?

HerrCai0907 commented 2 weeks ago

In high performance embedded device which has larger RAM than the traditional embedded device but not too much (>1M). In this case, 64kB per page is still to much granularity. Then it can use lowMemoryLimit to control the memory usage.

CountBleck commented 2 weeks ago

Does this do anything that --maximumMemory doesn't?

HerrCai0907 commented 2 weeks ago

Does this do anything that --maximumMemory doesn't?

maximumMemory is in 64kB size, but lowMemoryLimit is 16B size. But I agree we may can unify them.

CountBleck commented 2 weeks ago

Hmm, I think I'm confused. If you have more than 64 KiB of memory on your device, wouldn't --maximumMemory work?

Or are you restricted to an amount of memory that's not a multiple of 64 KiB (for instance, 68 KiB, 123 KiB, etc.)?

HerrCai0907 commented 2 weeks ago

Or are you restricted to an amount of memory that's not a multiple of 64 KiB (for instance, 68 KiB, 123 KiB, etc.)?

Yes. For example, I have device with 150kB memory but want to run 2 wasm job. It is impossible to split 3 x 64kB linear memory. By this option, each job can use 75kB.

Some background: Lots of runtime use virtual memory which will not commit the linear memory from memory.grow utill it is really used. So the memory.grow will / can success even we don't have so many physical memory. When WASM want to write some data in linear memory, it will commit it and make it writable. But AS's allocator will write information at the end of linear memory, which will make runtime commit the whole linear memory. Then when runtime wants to commit the memory, it will trigger OOM and be killed.