[Experiment] purge-and-suspend

third_party/WebKit/Source/core/dom/StyleEngine.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 793 matching lines @@
 {
     if (m_hasUnresolvedKeyframesRule) {
         m_hasUnresolvedKeyframesRule = false;
         document().setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::StyleSheetChange));
         return;
     }
 
     document().timeline().invalidateKeyframeEffects();
 }
 
+void StyleEngine::purgeMemory()
+{
+    clearFontCache();
+    clearResolver();

[esprehn, 2016/08/05 23:00:58]

I think this has some scary side effects, you should double check with rune@,
this also leaves all of the ScopedStyleResolvers. It's going to make us recalc
the entire document I think too.

[tasak, 2016/08/08 04:47:36]

Acknowledged.

I would like to ask one thing. Are you talking about "background to foreground"
full recalc?
As far as I understand, background tabs are suspended and need no layout, no
stylerecalc, and no painting.

+    m_textToSheetCache.clear();
+    m_sheetToTextCache.clear();

[esprehn, 2016/08/05 23:00:58]

This code doesn't really make sense, you're leaving around all of the
ScopedStyleResolvers and the CSSStyleSheet which were created from these
strings. Are you sure this actually saves memory? It shouldn't, the cache here
is just for looking up stuff the rest of the DOM is already using

[tasak, 2016/08/08 04:47:36]

Acknowledged.
I agree that basically these caches' sizes are small and that the impact is very
small.

+}
+
 DEFINE_TRACE(StyleEngine)
 {
     visitor->trace(m_document);
     visitor->trace(m_injectedAuthorStyleSheets);
     visitor->trace(m_documentStyleSheetCollection);
     visitor->trace(m_styleSheetCollectionMap);
     visitor->trace(m_resolver);
     visitor->trace(m_styleInvalidator);
     visitor->trace(m_dirtyTreeScopes);
     visitor->trace(m_activeTreeScopes);
     visitor->trace(m_fontSelector);
     visitor->trace(m_textToSheetCache);
     visitor->trace(m_sheetToTextCache);
     CSSFontSelectorClient::trace(visitor);
 }
 
 DEFINE_TRACE_WRAPPERS(StyleEngine)
 {
     for (auto sheet : m_injectedAuthorStyleSheets) {
         visitor->traceWrappers(sheet);
     }
     visitor->traceWrappers(m_documentStyleSheetCollection);
 }
 
 } // namespace blink