[Webkit-unassigned] [Bug 170690] New: WebAssembly: report Memory usage to GC

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Apr 10 13:42:42 PDT 2017


https://bugs.webkit.org/show_bug.cgi?id=170690

            Bug ID: 170690
           Summary: WebAssembly: report Memory usage to GC
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jfbastien at apple.com
                CC: jfbastien at apple.com
        Depends on: 170628
            Blocks: 159775

As part of bug #170628 I noticed that we never report the memory allocated by WebAssembly.Memory to the GC. This change would do it:

Wasm::PageCount JSWebAssemblyMemory::grow(VM& vm, ExecState* exec, uint32_t delt
...
    vm.heap.reportExtraMemoryAllocated(Wasm::PageCount(delta).bytes());

void JSWebAssemblyMemory::finishCreation(VM& vm)
...
    heap()->reportExtraMemoryAllocated(m_memory->size());

JSWebAssemblyMemory::visitChildren(JSCell* cell, SlotVisitor& visitor)
...
    visitor.reportExtraMemoryVisited(thisObject->memory().size());


I'm not sure it's the right thing to do though! The "initial" size seems like a good thing to report, but if we haven't actually backed it up with physical pages then it may severely over-estimate allocation and cause the GC to run too much.

This change is significant enough that I'll punt it to its own patch, after bug #170628.


Referenced Bugs:

https://bugs.webkit.org/show_bug.cgi?id=159775
[Bug 159775] WebAssembly: support the newer spec
https://bugs.webkit.org/show_bug.cgi?id=170628
[Bug 170628] WebAssembly: manage memory better
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