bla.st : keep safari and osx running fast: work around the memory leaks.

Safari has a huge memory management issues. To be precise the problem is not with Safari, but WebKit, the engine that powers Safari and other browsers like OmniWeb. Sitting around moaning about it doesn't really help, but hopefully this will make clearer what problems some users, including myself, are having.

Basically the more pages you look at, the more memory your browser will use. The problem is WebKit does not release this memory back to the system until the application is quit. If you're a heavy web user, or like many people simply leave your browser continuously this becomes a major problem. Memory on MacOS X is complicated, but basically when your system runs out of memory, it starts paging other applications to disk. It gets to the point where opening new web pages is slow because it has to page something to disk, and switching to other applications is painfully slow because it has to load them back.

There is more discussion of the problem over on the webkit.org blog.

A simply but dirty solution is to simply quit and reopen Safari as soon as the system starts paging to disk. A memory monitor is a good investment too, I use iPulse to keep an eye on things. So when does Mac OS start paging to disk?

Activity Monitor

Memory on OS X is divided into 4 different types. Wired, Active, Inactive and Free. I have no idea what the all are exactly, although there are other artciles that explain it all. What I do know is when Inactive + Free reaches 70%, my system starts paging to disk and swapping memory around. iPules is good like this because it gives you that percentage figure, so you can easily keep an eye on it (see below). When I hit 69% of "in use" memory I know if I open another application, or keep browsing, something will be paged back to disk. Thanks to my PowerBook 4200rpm hard disk, this is painful and I avoid it where possible. Here's memory at it's upper limit:

Memory Usage

So why does WebKit not release memory back? I have no idea. I've tried everything you can think of. Closing windows. Clearing the cache. Turning the developers menu on, and clearning the WebKit cache's. I've even tried not using any cache at all. No matter what, the only way to reclaim memory is to quit the application.

So how fast does WebKit fill up with memory? It depends greatly on how many pages you are looking at, and what's on the pages. Sites that use a lot of images seem to chew up the memory quick. Generally I need to quit Safari or OmniWeb every couple of hours. It often reaches 300-400MB before I run out of memory I guess that WebKit is caching images and not giving that memory back.

So what's the solution? Well ideally OS X should always use as much memory as it can, but avoid paging to disk if possible. This means apps like Safari should cache as much as possible, but be intelligent enough to empty out the cache when memory starts running low. I don't know if this is possible, perhaps a simpler option is to let users set a limit of how much memory WebKit can use, much like Photoshop.

Unfortunately a number of other apps also suffer from a similar problem. iTunes CoverFlow is a great example - iTunes starts small, as album covers are viewed memory usage increases, switch back to list view and memory isn't freed up. Apple Mail does this viewing large attachments too. Is this a flaw with the individual applications? Or a more fundamental flaw with how OS X handles memory? I have an older application, Macromedia Freehand. If that loads a big file, it releases all of it when the window is closed. Why can't cocoa apps work like that?

Any thoughts or ideas? Can any Apple developers let us know what the story is? Leave comments at the WebKit Blog

Got a website? Promote it on bla.st free

Recent Entries

Older Entries

« bla.st Blog

Keep Safari and OSX running fast: Work around the memory leaks.