Bug 157945 - Web Inspector: retained size for typed arrays does not count native backing store
Summary: Web Inspector: retained size for typed arrays does not count native backing s...
Alias: None
Product: WebKit
Classification: Unclassified
Component: Web Inspector (show other bugs)
Version: WebKit Nightly Build
Hardware: All All
: P2 Normal
Assignee: Joseph Pecoraro
Keywords: InRadar
Depends on:
Reported: 2016-05-20 09:32 PDT by Brian Burg
Modified: 2016-05-20 14:46 PDT (History)
14 users (show)

See Also:

[SCREENSHOT] Bad timeline data (415.96 KB, image/png)
2016-05-20 09:34 PDT, Brian Burg
no flags Details
[PATCH] Proposed Fix (4.18 KB, patch)
2016-05-20 14:20 PDT, Joseph Pecoraro
no flags Details | Formatted Diff | Diff

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Description Brian Burg 2016-05-20 09:32:52 PDT

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


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


Retained size is 32 bytes regardless of typed array size
Comment 1 Radar WebKit Bug Importer 2016-05-20 09:33:20 PDT
Comment 2 Brian 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 = [];
    var buffer = new ArrayBuffer(4*5000);
    var view = new Float32Array(buffer);

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

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.