When using about:memory to hunt down memory leaks, sometimes you really want to run a GC and/or CC to ensure that all garbage has been collected. We probably want three buttons: "GC", "CC", and "GC + CC". I've heard that sometimes you need multiple runs of both to get all the garbage, so the "GC + CC" button could do this.

Yes, the CC only frees DOM objects, and the GC only frees JS objects, so if there's a garbage cycle made up of both, it could take something like GC -> CC -> GC to clear it out.

Oops, I guess you are just running a CC here, not dumping a graph, so never mind about that dependency I added.

BTW, to do this I need to find out how to trigger GC and CC from JavaScript. I thought gc() did GC but now I see that's only in the shell. Any suggestions are welcome.

There is nsIDOMWindowUtils.garbageCollect and Components.utils.forceGC. You can figure out which does what because I don't really know.

I'd like to also have a button that fires a memory-pressure notification (like RAMBack). It could be labeled "GC, CC, and flush caches". This code fires a notification: Components.classes["@mozilla.org/observer-service;1"] .getService(Components.interfaces.nsIObserverService) .notifyObservers(null, "memory-pressure", "heap-minimize"); Caches are expected to listen for memory-pressure notifications and clear themselves [1]. For example, it causes all bfcache pages to be evicted [2]. It also triggers a GC and a CC [3]. [1] https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsIMemory#Low_memory_notifications [2] http://hg.mozilla.org/mozilla-central/annotate/84af3e2c7ac3/docshell/shistory/src/nsSHistory.cpp#l120 [3] http://hg.mozilla.org/mozilla-central/annotate/84af3e2c7ac3/dom/base/nsJSEnvironment.cpp#l195

The code in this add-on should be helpful: https://addons.mozilla.org/en-US/firefox/addon/ramback/ :)

This patch adds three buttons: "GC", "GC + CC", and "Minimize memory usage". (Screenshot coming shortly.) The 2nd button is "GC + CC" instead of just "CC" because of bug 625302. This works great on desktop; I used to console to check that the GCs/CCs were occurring. On Fennec it's less useful as the events only apply to the main (chrome) process. I imagine triggering the events in the content proces would require some complicated IPC. I guess the question is whether this patch is good enough for now?

Comment on attachment 530548 [details] [diff] [review] patch Asking Vlad for the review because I can't think of anyone better.

Awesome stuff. shaver can review as well. He hacked on in quite a bit.

> + // Do it three times, just to be sure. > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); For maximum effect, you want to return to the event loop between these notifications. See bug 610166 comment 12 for an example of why. http://pastebin.mozilla.org/1219590 shows the code I use to return to the event loop. > "triggers a global garbage collection followed by a cycle collection, and > may cause the process to reduce other memory usage, e.g. by flushing caches." The use of "may" here makes it seem like the cache-flushing effect is less certain than the garbage-collection effect, or less certain to reduce memory use. Would "... followed by a cycle collection, and flushes many caches" be accurate enough?

Just in case it disappears from pastebin some time in the future.

(In reply to comment #11) > > For maximum effect, you want to return to the event loop between these > notifications. Good to know, thanks. > > "triggers a global garbage collection followed by a cycle collection, and > > may cause the process to reduce other memory usage, e.g. by flushing caches." > > The use of "may" here makes it seem like the cache-flushing effect is less > certain than the garbage-collection effect, or less certain to reduce memory > use. > > Would "... followed by a cycle collection, and flushes many caches" be > accurate enough? Sure, I'll change it.

Comment on attachment 530548 [details] [diff] [review] patch Looks reasonable.

I filed bug 655647 as a follow-up for working with child processes; I want to get this in quickly (ie. for Firefox 6) because it's fully functional for desktop Firefox.

(In reply to comment #11) > > + // Do it three times, just to be sure. > > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); > > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); > > + os.notifyObservers(null, "memory-pressure", "heap-minimize"); > > For maximum effect, you want to return to the event loop between these > notifications. See bug 610166 comment 12 for an example of why. > http://pastebin.mozilla.org/1219590 shows the code I use to return to the > event loop. I'm not sure that we want to do that. If we need multiple GCs or CCs or event loop trips that's (at least IMO) a bug that should be fixed.

This version goes back to the event loop for each notification, as per Jesse's suggestion.

Looks like this patch runs 3 memory-pressure notifications, but calls update() after the first one. I think you want to update() after the last one instead.

This version uses runSoon() to call update() after the notifications have occurred.

Comment on attachment 530981 [details] [diff] [review] patch v3 Looks good to me.

Verified on the latest Nightly: Mozilla/5.0 (Windows NT 6.1; rv:7.0a1) Gecko/20110703 Firefox/7.0a1