Throw away StyleResolvers that haven't been used for a long time.

<http://webkit.org/b/104314>

Reviewed by Antti Koivisto.

A lot of memory gets tied up in StyleResolver and the structures and caches that hang from it.
Add a mechanism to throw it away after it's been unused for a while (1 minute.)
This frees up large amounts of memory on inactive pages (background tabs) and static content.

We already have a number of scenarios where the document style is invalidated by throwing away
the StyleResolver so the major code paths are prepared for having a null StyleResolver* on occasion.

~20MB progression on Membuster3.

* css/StyleResolver.cpp:
(WebCore::StyleResolver::styleForElement):
(WebCore::StyleResolver::styleForKeyframe):
(WebCore::StyleResolver::pseudoStyleForElement):
(WebCore::StyleResolver::styleForPage):

    Call document()->didAccessStyleResolver() from the relevant parts of StyleResolver's public API.
    This prevents Document from throwing the StyleResolver away for 1 minute after it's used.

* dom/Document.h:
* dom/Document.cpp:
(WebCore::Document::Document):
(WebCore::Document::createStyleResolver):
(WebCore::Document::didAccessStyleResolver):
(WebCore::Document::styleResolverThrowawayTimerFired):

    Add a mechanism to call clearStyleResolver() on a refreshing timer.

* dom/Element.cpp:
(WebCore::Element::attributeChanged):

    If an attribute change occurs while the document doesn't have a StyleResolver, dirty the element style
    since we can't be sure that the attribute change didn't affect any rules.


Canonical link: https://commits.webkit.org/122531@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@136956 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,43 @@
+2012-12-07  Andreas Kling  <akling@apple.com>
+
+        Throw away StyleResolvers that haven't been used for a long time.
+        <http://webkit.org/b/104314>
+
+        Reviewed by Antti Koivisto.
+
+        A lot of memory gets tied up in StyleResolver and the structures and caches that hang from it.
+        Add a mechanism to throw it away after it's been unused for a while (1 minute.)
+        This frees up large amounts of memory on inactive pages (background tabs) and static content.
+
+        We already have a number of scenarios where the document style is invalidated by throwing away
+        the StyleResolver so the major code paths are prepared for having a null StyleResolver* on occasion.
+
+        ~20MB progression on Membuster3.
+
+        * css/StyleResolver.cpp:
+        (WebCore::StyleResolver::styleForElement):
+        (WebCore::StyleResolver::styleForKeyframe):
+        (WebCore::StyleResolver::pseudoStyleForElement):
+        (WebCore::StyleResolver::styleForPage):
+
+            Call document()->didAccessStyleResolver() from the relevant parts of StyleResolver's public API.
+            This prevents Document from throwing the StyleResolver away for 1 minute after it's used.
+
+        * dom/Document.h:
+        * dom/Document.cpp:
+        (WebCore::Document::Document):
+        (WebCore::Document::createStyleResolver):
+        (WebCore::Document::didAccessStyleResolver):
+        (WebCore::Document::styleResolverThrowawayTimerFired):
+
+            Add a mechanism to call clearStyleResolver() on a refreshing timer.
+
+        * dom/Element.cpp:
+        (WebCore::Element::attributeChanged):
+
+            If an attribute change occurs while the document doesn't have a StyleResolver, dirty the element style
+            since we can't be sure that the attribute change didn't affect any rules.
+
 2012-12-07  Antonio Gomes  <a1.gomes@sisa.samsung.com>
 
         REGRESSION(r136947): Made two tests fail on all platforms (Requested by tonikitoo-ll on #webkit).

Source/WebCore/css/StyleResolver.cpp

@@ -1601,6 +1601,8 @@ PassRefPtr<RenderStyle> StyleResolver::styleForElement(Element* element, RenderS
     if (cloneForParent)
         m_parentStyle = 0;
 
+    document()->didAccessStyleResolver();
+
     // Now return the style.
     return m_style.release();
 }
@@ -1654,6 +1656,8 @@ PassRefPtr<RenderStyle> StyleResolver::styleForKeyframe(const RenderStyle* eleme
         }
     }
 
+    document()->didAccessStyleResolver();
+
     return m_style.release();
 }
 
@@ -1757,6 +1761,8 @@ PassRefPtr<RenderStyle> StyleResolver::pseudoStyleForElement(PseudoId pseudo, El
     // Start loading resources referenced by this style.
     loadPendingResources();
 
+    document()->didAccessStyleResolver();
+
     // Now return the style.
     return m_style.release();
 }
@@ -1796,6 +1802,8 @@ PassRefPtr<RenderStyle> StyleResolver::styleForPage(int pageIndex)
     // Start loading resources referenced by this style.
     loadPendingResources();
 
+    document()->didAccessStyleResolver();
+
     // Now return the style.
     return m_style.release();
 }

Source/WebCore/dom/Document.cpp

@@ -437,6 +437,8 @@ Document::Document(Frame* frame, const KURL& url, bool isXHTML, bool isHTML)
     : ContainerNode(0, CreateDocument)
     , TreeScope(this)
     , m_guardRefCount(0)
+    , m_styleResolverThrowawayTimer(this, &Document::styleResolverThrowawayTimerFired)
+    , m_lastStyleResolverAccessTime(0)
     , m_contextFeatures(ContextFeatures::defaultSwitch())
     , m_compatibilityMode(NoQuirksMode)
     , m_compatibilityModeLocked(false)
@@ -4433,6 +4435,24 @@ void Document::sharedObjectPoolClearTimerFired(Timer<Document>*)
     m_sharedObjectPool.clear();
 }
 
+void Document::didAccessStyleResolver()
+{
+    static const int timeBeforeThrowingAwayStyleResolverAfterLastUseInSeconds = 60;
+    static const int holdOffTimeBeforeReschedulingTimerInSeconds = 5;
+
+    double currentTime = WTF::currentTime();
+
+    if (currentTime > m_lastStyleResolverAccessTime + holdOffTimeBeforeReschedulingTimerInSeconds) {
+        m_styleResolverThrowawayTimer.startOneShot(timeBeforeThrowingAwayStyleResolverAfterLastUseInSeconds);
+        m_lastStyleResolverAccessTime = currentTime;
+    }
+}
+
+void Document::styleResolverThrowawayTimerFired(Timer<Document>*)
+{
+    clearStyleResolver();
+}
+
 PassRefPtr<XPathExpression> Document::createExpression(const String& expression,
                                                        XPathNSResolver* resolver,
                                                        ExceptionCode& ec)

Source/WebCore/dom/Document.h

@@ -496,6 +496,8 @@ class Document : public ContainerNode, public TreeScope, public ScriptExecutionC
      */
     void styleResolverChanged(StyleResolverUpdateFlag);
 
+    void didAccessStyleResolver();
+
     void evaluateMediaQueryList();
 
     // Never returns 0.
@@ -1260,6 +1262,10 @@ class Document : public ContainerNode, public TreeScope, public ScriptExecutionC
 
     int m_guardRefCount;
 
+    void styleResolverThrowawayTimerFired(Timer<Document>*);
+    Timer<Document> m_styleResolverThrowawayTimer;
+    double m_lastStyleResolverAccessTime;
+
     OwnPtr<StyleResolver> m_styleResolver;
     bool m_didCalculateStyleResolver;
     bool m_hasDirtyStyleResolver;

Source/WebCore/dom/Element.cpp

@@ -799,6 +799,9 @@ void Element::attributeChanged(const QualifiedName& name, const AtomicString& ne
 
     invalidateNodeListCachesInAncestors(&name, this);
 
+    // If there is currently no StyleResolver, we can't be sure that this attribute change won't affect style.
+    shouldInvalidateStyle |= !styleResolver;
+
     if (shouldInvalidateStyle)
         setNeedsStyleRecalc();