Bug 108229 - CSS matched properties cache exploding when mapped SVG attributes are updated frequently
Summary: CSS matched properties cache exploding when mapped SVG attributes are updated...
Alias: None
Product: WebKit
Classification: Unclassified
Component: CSS (show other bugs)
Version: 528+ (Nightly build)
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Florin Malita
Depends on: 108345
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Reported: 2013-01-29 14:30 PST by Florin Malita
Modified: 2022-07-13 13:57 PDT (History)
7 users (show)

See Also:

Leaks memory, eventually crashes Chromium. (2.27 KB, text/html)
2013-01-29 14:30 PST, Florin Malita
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Description Florin Malita 2013-01-29 14:30:06 PST
Created attachment 185308 [details]
Leaks memory, eventually crashes Chromium.


Several issues at play here:

1) the matched properties cache is never swept:


    if (++m_matchedPropertiesCacheAdditionsSinceLastSweep >= matchedDeclarationCacheAdditionsBetweenSweeps) {
        static const unsigned matchedDeclarationCacheSweepTimeInSeconds = 60;

Since we keep updating the props, the timer keeps getting reset and never fires. I'll post a patch to leave the timer alone if already armed.

2) matched SVG properties are cacheable

I'm not familiar with this area, but it seems strange that SVG attributes result in cacheable matched properties, while the equivalent CSS test (divs, background-color updates) yields non-cacheable matched properties.

For inline style we explicitly make a caching decision:
        // Inline style is immutable as long as there is no CSSOM wrapper.
        // FIXME: Media control shadow trees seem to have problems with caching.
        bool isInlineStyleCacheable = !m_styledElement->inlineStyle()->isMutable() && !m_styledElement->isInShadowTree();

while for presentational attributes we never re-evaluate cacheability based on isMutable.

I don't understand enough of what's going on here to call it a bug, but it does seem a bit odd to have this asymmetry - someone should confirm that it's intended.

3) SVG matched properties do not get a deterministic matched properties hash key

This is because StyledElement::makePresentationAttributeCacheKey() doesn't support SVG attributes:

void StyledElement::makePresentationAttributeCacheKey(PresentationAttributeCacheKey& result) const
    // FIXME: Enable for SVG.
    if (namespaceURI() != xhtmlNamespaceURI)

=> SVG StylePropertySets are effectively non-cacheable (in the presentation attribute cache)
=> rebuildPresentationAttributeStyle() always allocates a new StylePropertySet
=> the hash computed in StyleResolver::applyMatchedProperties() is always different (is based on MatchedProperties contents which bundles pointers to StylePropertySets)
=> SVG matched properties are always added to the matched properties cache, even if equivalent entries already exist

This probably needs fixing: add SVG support to StyledElement::makePresentationAttributeCacheKey() to enable proper SVG data hashing in both the presentation attribute cache and the matched properties cache.
Comment 1 Florin Malita 2013-02-01 13:12:49 PST
Andreas, Antti: I'm not familiar with styling and trying to understand what the correct high-level behavior should be here.

For a CSS test where I'm modifying 'background-color' on a <div> dynamically, the resulting MatchResult is non-cacheable because of the following snippet in StyleResolver::matchAllRules():

    // Now check our inline style attribute.
    if (m_matchAuthorAndUserStyles && m_styledElement && m_styledElement->inlineStyle()) {
        // Inline style is immutable as long as there is no CSSOM wrapper.
        // FIXME: Media control shadow trees seem to have problems with caching.
        bool isInlineStyleCacheable = !m_styledElement->inlineStyle()->isMutable() && !m_styledElement->isInShadowTree();
        // FIXME: Constify.
        addElementStyleProperties(result, m_styledElement->inlineStyle(), isInlineStyleCacheable);

Is the intent to prevent caching of script-modifiable matched properties? That would make sense, since with a 1 min purge timer on the matched properties cache one could use up lots of memory otherwise.

But for SVG attributes there is no such mechanism - the resulting matched properties are cached unconditionally on the presentational attributes path:

    // Now check author rules, beginning first with presentational attributes mapped from HTML.
    if (m_styledElement) {
        addElementStyleProperties(result, m_styledElement->presentationAttributeStyle());

I guess the question is: should SVG attributes always yield non-cacheable matched properties?
Comment 2 Brent Fulgham 2022-07-13 13:57:14 PDT
WebKit seems to use the least amount of memory or other resources (compared to Blink and Gecko).