Bug 157945

Summary: Web Inspector: retained size for typed arrays does not count native backing store
Product: WebKit Reporter: BJ Burg <bburg>
Component: Web InspectorAssignee: Joseph Pecoraro <joepeck>
Status: RESOLVED FIXED    
Severity: Normal CC: bburg, commit-queue, fpizlo, ggaren, graouts, joepeck, keith_miller, mark.lam, mattbaker, msaboff, nvasilyev, saam, timothy, webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: All   
OS: All   
See Also: https://bugs.webkit.org/show_bug.cgi?id=78574
Attachments:
Description Flags
[SCREENSHOT] Bad timeline data
none
[PATCH] Proposed Fix none

Description BJ Burg 2016-05-20 09:32:52 PDT 
STEPS TO REPRODUCE

1. Go to http://bl.ocks.org/syntagmatic/6c149c08fc9cde682635
2. Capture a recording long enough that a really big GC happens
3. Compare heap snapshots before and after a big GC

EXPECTED

It lists a Float32Array and ArrayBuffer with 10's of thousands of elements, so it should be MB's of data

ACTUAL

Retained size is 32 bytes regardless of typed array size
Comment 1 Radar WebKit Bug Importer 2016-05-20 09:33:20 PDT 
<rdar://problem/26392238>
Comment 2 BJ Burg 2016-05-20 09:34:44 PDT 
Created attachment 279483 [details]
[SCREENSHOT] Bad timeline data
Comment 3 Joseph Pecoraro 2016-05-20 12:22:31 PDT 
I guess this is a specific type of TypedArray that we do not get the size correctly.

For a basic:

    new Uint32Array(5000);

I'm seeing it get a size of 19.56kb.

So there must be something non-trivial about the arrays on that page.
Comment 4 Joseph Pecoraro 2016-05-20 13:35:07 PDT 
Ahh, I see the issue when using a Buffer and View separately:

    window.lists = [];
    console.takeHeapSnapshot("before");
    var buffer = new ArrayBuffer(4*5000);
    var view = new Float32Array(buffer);
    window.lists.push(view);
    console.takeHeapSnapshot("after");    

Neither the ArrayBuffer or the Float32Array claiming the data!
Comment 5 Joseph Pecoraro 2016-05-20 13:40:13 PDT 
Looks like JSArrayBuffer doesn't report an estimated size. I missed it because ArrayBuffer's have their own unique reporting of their size to the Heap.
Comment 6 Joseph Pecoraro 2016-05-20 14:20:37 PDT 
Created attachment 279501 [details]
[PATCH] Proposed Fix

Note, with this change, the memory will be associated with the ArrayBuffer.

There currently does not exist a way to know if the Float32Array is the only retainer of the ArrayBuffer, so the Float32Array's will still appear small. That means they are just a view on an ArrayBuffer.
Comment 7 Geoffrey Garen 2016-05-20 14:25:39 PDT 
Comment on attachment 279501 [details]
[PATCH] Proposed Fix

r=me
Comment 8 WebKit Commit Bot 2016-05-20 14:46:16 PDT 
Comment on attachment 279501 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 279501

Committed r201226: <http://trac.webkit.org/changeset/201226>
Comment 9 WebKit Commit Bot 2016-05-20 14:46:23 PDT 
All reviewed patches have been landed.  Closing bug.