[Webkit-unassigned] [Bug 28819] Heap profiler: showing retainers

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Oct 5 02:31:33 PDT 2009


--- Comment #4 from Mikhail Naganov <mnaganov at chromium.org>  2009-10-05 02:31:33 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> > Created an attachment (id=39637)
 --> (https://bugs.webkit.org/attachment.cgi?id=39637) [details] [details]
> > Update version of UI
> > 
> > I re-thinked about retainers, and experimented with real web apps. This
> > radically changed my mind. I discovered that it is possible to put retainers
> > graph into every snapshot in a reduced form. That is, retainments are tracked
> > not for individual objects but rather for objects constructed with the same
> > function. The only problem here is with anonymous Object and Array instances.
> > For them, initially we consider every instance, but then we are aggregating
> > them by similarity of their backreferences (in short, if two Object instances
> > are held by instances of the same constructor, they are considered equivalent.)
> > 
> > Thus, we don't need an additional pane, and instead can show retainers
> > naturally in the heap snapshot. To help a developer to prioritize back
> > references, we should show how many object instances are retained for every
> > backreference (e.g. objects of 'baz' constructor can be held by 'foo' and
> > 'bar', of which 'foo' holds 90% of objects and 'bar' only 10%). I don't think
> > we need to display the number of retained objects for next levels, because it's
> > expensive to count them. Also I'm not sure whether we always could display
> > deltas: it seems OK for named constructors, but for Objects and Arrays it's
> > hard to find corresponding entries in two snapshots (we can't even use real
> > memory addresses, because objects may get moved during GC.)
> I like this approch! I assume "bar-retainer" is the name of the object (not you
> adding "-retainer" to it?

Sure, I'm not modifying constructor names. I just called it so for
demonstration purposes.

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