All windows have the same style data for :viewport and :viewport-scroll. We get back 5-10% on pretty much all XUL windows if we cache this data once, globally, and reuse it when resolving these pseudos for any document (HTML, XML, or XUL).
Status: NEW → ASSIGNED
Target Milestone: --- → mozilla0.9
Does Pierre's work on bug 43457 take care of this already?
IMHO :viewport, :viewport-scroll, :canvas, :scrolled-content, :wrapped-frame, and :placeholder-frame, and maybe some others, should all be replaced by hard- coded frames that have hard-coded, prefilled and brutally shared style contexts. Or something. It sounded better when Hyatt said it. Either way, is there really any reason why it is better for us to use pseudo- elements that are only ever mentioned once (in ua.css)? It seems to me that if they were hard coded things would be much more sensible... But what do I know...
I would tend to say that we should fix this (i.e., move from :viewport and friends to hardcoded frames) even if it becomes irrelevant with the fix for bug 43457, but at a much lower priority.
If the style context for :viewport-scroll is a child of the style context for :viewport, then the fix for bug 43457 will mostly take care of it. We'll continue to allocate 2 StyleContextImpl (average size 71 bytes) and 2 nsStyleContextData. The difference is that the 2 nsStyleContextData currently take 764*2 = 1528 bytes that will be reduced to 884+68 = 952 bytes after the fix is checked in. As noted in bug 43457, the savings in XUL documents (or at least navigator.xul and messenger.xul) isn't as high as in HTML documents. It seemed to me that it was because XUL documents were generating much more CSSDeclarations and StyleRules. If the problem comes in fact from the number of style contexts that have a null parent (and for which we allocate the entire style data), I can look into it and see if the idea of a global style context makes sense. Some measurements I took 2 weeks ago on HTML pages showed that less than 1% of the style contexts have a null parent. Maybe the number is higher with XUL documents.
Pierre, I'm going to give this to you. I suspect your changes make this bug moot, so you can just close it out as a dup.
Assignee: hyatt → pierre
Status: ASSIGNED → NEW
I'm marking it Future because memory optimizations (StyleContext sharing or StyleData sharing) cannot be applied to the :viewport and other scrolling elements. The complete list is in nsStyleContext.cpp: nsLayoutAtoms::viewportPseudo nsLayoutAtoms::canvasPseudo nsLayoutAtoms::viewportScrollPseudo nsLayoutAtoms::scrolledContentPseudo nsLayoutAtoms::selectScrolledContentPseudo The problem was originally found by Marc when he worked on bug 39618. Changed the summary line from ":viewport and :viewport-scroll style data should be global" to "apply memory optimizations to :viewport and :viewport-scroll".
Status: NEW → ASSIGNED
Summary: :viewport and :viewport-scroll style data should be global → apply memory optimizations to :viewport and :viewport-scroll
Target Milestone: mozilla0.9 → Future
Sounds XP: marking All/All.
OS: Windows 2000 → All
Hardware: PC → All
bug 78695 made this one obsolete
Status: ASSIGNED → RESOLVED
Last Resolved: 18 years ago
Resolution: --- → WONTFIX
Status: RESOLVED → VERIFIED
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