Bug 31237 – REGRESSION (r47022): Performance of DocumentFragment.appendChild is 1000x slower sometimes

• Status: RESOLVED
• Resolution: FIXED
• Component: DOM

[Keishi Hattori]

I noticed the Web Inspector syntax highlighter was way too slow. It seems that DocumentFragment.appendChild is very very slow just in the latest WebKit nightly.

Test: Open http://keishi.net/SourceSyntaxHighlighter3/ and look at console

WebKit nightly(r50616) - 4241ms
Chromium nightly(4.0.240.0 (31395)) - 1494ms
Safari 4(4.0.3 (6531.9)) - 1487ms

[Keishi Hattori]

Also Node.appendChild(DocumentFragment) much slower in Safari than Chromium.

http://keishi.net/SourceSyntaxHighlighter4/

WebKit nightly(r50616) - 4478ms
Chromium nightly(4.0.240.0 (31395)) - 2581ms
Safari 4(4.0.3 (6531.9)) - 4354ms

[Mark Rowe (bdash)]

<rdar://problem/7375325>

[Keishi Hattori]

Created attachment 42952 [details]
reduced test case

[Keishi Hattori]

Created attachment 42953 [details]
test case results

I pressed each button once and then the last one one more time.

WebKit nightly is always extremely slow for "appendChild( DocumentFragment with 10000 childNodes )" test.  "DocumentFragment.appendChild(span) x10000" and "div.appendChild(span) x10000" is OK 50% of the time but 1000x slower for the other 50%.

[Keishi Hattori]

I've tracked the regression somewhere between r47011 and r47060.

[Keishi Hattori]

Judging from my profile results, http://trac.webkit.org/changeset/47022 looks suspicious...

[Oliver Hunt]

I agree with keishi - shark blames marking (98% in jsnode marking):
	1.1%	98.2%	WebCore	338 B	WebCore::JSNode::markChildren(JSC::MarkStack&)

[Timothy Hatcher]

*** Bug 31409 has been marked as a duplicate of this bug. ***

[Darin Adler]

We figured out the cause. It's the DOM node mark function. Maciej and Oliver are talking about solutions.

[Maciej Stachowiak]

Created attachment 43426 [details]
preliminary patch (haven't made sure it compiles and passes tests yet)

[Darin Adler]

Comment on attachment 43426 [details]
preliminary patch (haven't made sure it compiles and passes tests yet)

Looks good.

[Maciej Stachowiak]

Created attachment 43474 [details]
Patch

[Maciej Stachowiak]

(the new patch actually passes tests; first version broke Acid3)

[Oliver Hunt]

Comment on attachment 43474 [details]
Patch

r=me

[Maciej Stachowiak]

Committed r51162: <http://trac.webkit.org/changeset/51162>

[Alexey Proskuryakov]

The assumption in this patch was not quite correct, fragment roots don't always have wrappers. Fixed one hang resulting from that in bug 37181, but there might be more.