Document how to set memory limits

[Marcono1234]

If possible, could you please extend the documentation regarding how to set memory limits? Currently the documentation just says "set limits" but without telling how exactly.

• Describe it and add an example to the Resource Limits page
• Link to it from the Security Model page ("Memory growth limits"), similar to the existing "CPU Limits" link
• Possibly extend the Advanced Wasm Memory Customization page

The documentation regarding CPU limits is already pretty good, but for memory limits it is not directly clear how to apply them.

If I understand it correctly the main class is MemoryLimits, and it can be applied with Instance.Builder#withMemoryLimits. But what I don't fully understand yet is:

• Are there other places to consider?
  E.g. there is ImportMemory and MemoryImport, but I assume they are only relevant when you are actually importing memory?
• There is also TableLimits; is that relevant here as well?
• The limit specified using withMemoryLimits only seems to apply to memory index 0, is that intentional and does that mean the other memories are not restricted (besides the limit which is specified in the Wasm code itself)?
• The instructions array.new, array.new_default, array.new_fixed, array.new_data and array.new_elem create a new long[len] and don't seem to be restricted at all?

[andreaTP]

Thanks for rising this one.

I never attempted to formalize how to enforce Memory Limits, as they are intertwined with "how you built the wasm payload".
This open the doors to dragons(look at linker flags for TinyGo for example).

• other places: yes, MemoryImport only kicks in when using imported memories
• TableLimits: I never felt the need to tweak this one so far
• memory 0: yes, multi-memory support has been added recently, I'd consider extending the settings when necessity comes
• array. are instructions coming from WasmGC and they are, by construction, bound to i32 for the size