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

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=28819


Mikhail Naganov <mnaganov at chromium.org> changed:

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--- Comment #2 from Mikhail Naganov <mnaganov at chromium.org>  2009-09-16 03:04:16 PDT ---
Created an attachment (id=39637)
 --> (https://bugs.webkit.org/attachment.cgi?id=39637)
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.)

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