1487234 - Consider shrinking the Performance object

Status: NEW

(Core :: DOM: Core & HTML, defect, P3)

Description

[Boris Zbarsky [:bzbarsky]]

Performance is eagerly allocated when we create a Window, so we can rely on it  being in a slot for performance.now().  But a Performance object is not that small (looks like an 8KB allocation).  Might be worth shrinking it down some by lazily allocating some of its members.

From a DMD log:

Unreported {
  40 blocks in heap block record 59 of 6,988
  327,680 bytes (170,240 requested / 157,440 slop)
  Individual block sizes: 8,192 x 40
  0.07% of the heap (28.63% cumulative)
  0.18% of unreported (77.77% cumulative)
  Allocated at {
    #01: replace_malloc(unsigned long) (DMD.cpp:1267, in libmozglue.dylib)
    #02: moz_xmalloc (mozalloc.cpp:71, in libmozglue.dylib)
    #03: mozilla::dom::Performance::CreateForMainThread(nsPIDOMWindowInner*, nsIPrincipal*, nsDOMNavigationTiming*, nsITimedChannel*) (mozalloc.h:136, in XUL)
    #04: nsPIDOMWindowInner::CreatePerformanceObjectIfNeeded() (RefPtr.h:64, in XUL)
    #05: nsPIDOMWindowInner::GetPerformance() (RefPtr.h:296, in XUL)
    #06: mozilla::dom::Window_Binding::get_performance(JSContext*, JS::Handle<JSObject*>, nsGlobalWindowInner*, JSJitGetterCallArgs) (.WindowBinding.cpp:4356, in XUL)
    #07: mozilla::dom::Window_Binding::ClearCachedPerformanceValue(JSContext*, nsGlobalWindowInner*) (.WindowBinding.cpp:17051, in XUL)
    #08: nsGlobalWindowInner::InnerSetNewDocument(JSContext*, nsIDocument*) (nsGlobalWindowInner.cpp:7508, in XUL)
  }
}