[WASM] 4GB address space

[htdag]

Consider -s MAXIMUM_MEMORY=4GB emcc flag and it's implications for mono VM codebase.
Review other aspects, which may prevent handling large data.
Among others, how many copies of data we have at any time.

----- Original description
Got out of memory when load big file (~1GB) to memory.

// <InputFile OnChange="OnInputFileChange"
async Task OnInputFileChange(InputFileChangeEventArgs e)
{
    var file = e.File;
    using (var stream = file.OpenReadStream(file.Size))
    {
        var ms = new MemoryStream((int)file.Size);
        await stream.CopyToAsync(ms); // memory access out of bounds | Out of memory
        
        // ...
    }
}

=>

Uncaught (in promise) RuntimeError: memory access out of bounds
    at <anonymous>:wasm-function[120]:0x53cf
    at <anonymous>:wasm-function[3924]:0xc7ead
    at <anonymous>:wasm-function[3925]:0xc7f03
    at <anonymous>:wasm-function[1749]:0x43fd6
    at <anonymous>:wasm-function[3923]:0xc7e2b
    at <anonymous>:wasm-function[6542]:0x158b1e
    at Object.Module._mono_wasm_string_from_utf16 [as mono_wasm_string_from_utf16] (dotnet.6.0.0-preview.7.21377.19.js:1)
    at Object.js_string_to_mono_string_new (dotnet.6.0.0-preview.7.21377.19.js:1)
    at Object.js_string_to_mono_string (dotnet.6.0.0-preview.7.21377.19.js:1)
    at Object.converter_ssss [as compiled_function] (converter_ssss:11)

[pranavkm]

That error makes sense - you're reading the entire stream in to memory and the browser has much lower memory limits for the app. What is it that you're trying to do with the stream?

[htdag]

I need full load and process whole file (because OpenReadStream is not seekable)
I have ~5GB free but still out of memory,
possible to increase memory limit?

[pranavkm]

@lewing is there a way to increase the memory allocated to the WASM app? Do we know how the browser decides what the limits are?

[pranavkm]

Also, @SteveSandersonMS pointed out that V8 now allows WASM to allocate up to 4GB - https://v8.dev/blog/4gb-wasm-memory.

[lewing]

This is effective making multiple copies of a 1GB stream, it isn't surprising it is exhausting memory, we should examine what we can do in this sort of situation.

cc @pavelsavara

[SteveSandersonMS]

As far as I can tell from the code, it would only load the stream into an in-memory buffer once, since CopyToAsync is reading chunks from JS to populate the .NET buffer.

However if you do try to submit multiple 1GB files at once then of course it would load multiple into memory. Is that what you mean, @lewing?

Update I guess the JS side may need to allocate the whole 1GB buffer too. Also there was a separate bug reported at dotnet/aspnetcore#35540 (comment) which might be contributing if you are loading multiple files.

[pavelsavara]

At the moment I think we don't event set -s MAXIMUM_MEMORY=4GB emcc flag

[pranavkm]

@pavelsavara is that something we would consider setting? If so, should we transfer this issue over to the runtime to track for a future release?

[pavelsavara]

I guess it would be multiple things which would have to be fixed, not just this one.
Perhaps we should have well defined user story for this in 7.0 @lewing ?

[mkArtakMSFT]

Transferring over to the dotnet/runtime for consideration for 7.0.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.