2009/9/22 Matt Perry <[email protected]> > First, my question: what is the reason for the call > to i::Heap::CollectAllGarbageIfContextDisposed() in v8::Context::New? Is it > just a heuristic that can be removed? Or can we maybe add an API to disable > this in some cases? >
It's a heuristic. The idea is that when you navigate to a new page you will destroy a series of contexts (one per iframe) and then create a new context for the new main page. This is a good time to GC because it helps clear up the DOM nodes from the old page. > > The Chrome extension system introduces a feature called content scripts, > which allows you to run scripts in a new Context with a handle to the DOM > window of a target frame. The way this is implemented seems to trigger a > pathological case in v8::Context::New, causing more GCs than necessary. > > What happens is that content scripts create short-lived Contexts, where we > create the Context, run some script, and immediately Dispose of it. The call > to Dispose sets a flag in v8 which causes the next call to v8::Context::New > to trigger a GC. This means that any time 2+ content scripts are run in a > given process, we do a GC, slowing down page load. > > You can see the effect of running 50 content scripts on Chrome's startup > here: > http://build.chromium.org/buildbot/perf/xp-release/startup/report.html?history=20 > (the > top green line). If I comment out the call > to i::Heap::CollectAllGarbageIfContextDisposed(), the startup time for that > test is cut in half. > > > > -- Erik Corry, Software Engineer Google Denmark ApS. CVR nr. 28 86 69 84 c/o Philip & Partners, 7 Vognmagergade, P.O. Box 2227, DK-1018 Copenhagen K, Denmark. --~--~---------~--~----~------------~-------~--~----~ v8-dev mailing list [email protected] http://groups.google.com/group/v8-dev -~----------~----~----~----~------~----~------~--~---
