[wasm] Set -sMAXIMUM_MEMORY to 256 MiB by default

[lambdageek]

Mobile Safari (on ios 16.4 and probably earlier) doesn't like Emscripten's default MAXIMUM_MEMORY of 2 GiB:

wasmMemory=new WebAssembly.Memory({"initial":INITIAL_MEMORY/65536,"maximum":2147483648/65536,"shared":true})

We get a rejected promise during startup with RangeError: out of memory with the default maximum memory size.

As a workaround I can add this in my .csproj, but we should set a good default:

        <PropertyGroup Condition="'$(TargetFramework)' == 'net8.0'">
            <!-- 256 MiB -->
            <EmccFlags>-sMAXIMUM_MEMORY=268435456</EmccFlags>
        </PropertyGroup>

Note: we should double-check that 256 is a good default for Blazor

Note2: demo https://lambdageek.dev/dotnet-wasm-raytracer/net8/

[lewing]

Interesting, we definitely need to think about what a good default for this is.

[ghost]

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Mobile Safari (on ios 16.4 and probably earlier) doesn't like

wasmMemory=new WebAssembly.Memory({"initial":INITIAL_MEMORY/65536,"maximum":2147483648/65536,"shared":true})

That emscripten has by default, where 2147483648 is the default MAXIMUM_MEMORY.

We get a rejected promise during startup with RangeError: out of memory with the default maximum memory size.

As a workaround I can add this in my .csproj, but we should set a good default:

        <PropertyGroup Condition="'$(TargetFramework)' == 'net8.0'">
            <!-- 256 MiB -->
            <EmccFlags>-sMAXIMUM_MEMORY=268435456</EmccFlags>
        </PropertyGroup>

Note: we should double-check that 256 is a good default for Blazor

Note2: demo https://lambdageek.dev/dotnet-wasm-raytracer/net8/

Author:	lambdageek
Assignees:	maraf
Labels:	arch-wasm, area-Build-mono, needs-area-label
Milestone:	8.0.0

[maraf]

I think it's too late to change defaults and would prefer to start with in early .NET 9

[pavelsavara]

I can't find new WebAssembly.Memory statement in the dotnet.native.js anymore.

I can see Memory section in wa-info

Reading section:    Memory size:            7 count: 1
  memory: 0 limits: 256, 32768 has max: True

[lambdageek]

@maraf Can we think about adding an msbuild property for .net8 to set the maximum in a nice way instead of relying on EmccFlags. That way we don't change the default, but people who are interested in supporting iOS can set a maximum that it can use.

[maraf]

I can't find new WebAssembly.Memory statement in the dotnet.native.js anymore.

The new WebAssembly.Memory statement is there only in MT version. when wasm memory is marked as import. Anyway the passed max memory is used in getHeapMax

[pavelsavara]

Are we saying that setting max heap lower will make GC run earlier, and the browser would not have to allocate more than he can (on limited device) ?

Or we actually need to set initial memory ?

[pavelsavara]

we could also detect that we are on mobile safari and try to do it on runtime

const memory = new WebAssembly.Memory({
  initial: 10,
  maximum: 100,
});

[pavelsavara]

Also if this is only about Mono GC pressure I think we could have other means how to set it lower, without needing to make it compile time constant.

@radekdoulik I remember that you somehow detect available memory for GC purpose ?

[lambdageek]

I'm not sure what this has to do with Mono. Mobile Safari refuses to create the wasm memory instance if the maximum is more than 256MiB. Doesn't matter how Mono will use it. This happens much earlier

[ilonatommy]

Wasn't #91256 a fix for this? Do we need to keep the discussion open?

[lambdageek]

Wasn't #91256 a fix for this? Do we need to keep the discussion open?

#91256 made it easier for app authors to set the maximum initial memory. But we didn't change the default.

Maybe we don't need to change the default? Maybe we can just add something to the docs? or write something to the console if we detect mobile safari and the runtime fails to start?

[mkhamoyan]

Error message was added by #104963