Bug 81865 – Improve our style sharing algorithm parameters

• Status: NEW
• Component: CSS

[Julien Chaffraix]

Currently our style sharing algorithm uses those 2 values that I set a year ago:

static const unsigned cStyleSearchThreshold = 10;
static const unsigned cStyleSearchLevelThreshold = 10;

Those were set up to improve style sharing and instrumenting our style sharing, I don't think they are an optimum of performance vs memory savings.

My current discovery so far based on html5-full-render.html and moz, intl1, intl2 and alexa_us page cyclers:
* Our current style sharing rate is 28.6% (that is out of 1000 calls to locateSharedStyle, 286 returns a match)
* Most of the tree walking leads to bailing out without having a shared style (95% of the "budget" used by the algorithm (|count| and |visitedNode| in locateSharedStyle) fails |sharedNode| NULL-check)
* Overall, when styles are shared, we don't walk the tree that much (on average, |count| is around 1 and |visitedCount| is around 1 too).

What I am missing is the distribution of the parameters to know what would be an optimum.

[Julien Chaffraix]

Created attachment 133174 [details]
Patch for discussion about the trade-offs we are ready to make, not necessarily the best choice but a good example.

[Ahmad Saleem]

At least one of the threshold exist still even today:

https://github.com/WebKit/WebKit/blob/62782a8855305e19a8039168935016bb1b7ecfcf/Source/WebCore/style/StyleSharingResolver.cpp#L52

Is there any needed to look into on how to evolve this for any future refactoring or this can be tagged as "RESOLVED WONTFIX"? Thanks1