I'm trying to track down some peculiar memory behavior in my Cocoa desktop app. My app does a lot of image processing using NSImage and uploads those images to a website over HTTP using NSURLConnection.

After uploading several hundred images (some very large), when I run Instrument I get no leaks. I've also run through MallocDebug and get no leaks. When I dig into object allocations using Instrument I get output like this:

GeneralBlock-9437184, Net Bytes 9437184, # Net 1
GeneralBlock-192512, Net Bytes 2695168, # Net 14

and etc., for smaller sizes. When I look at these in detail, they're marked as being owned by 'Foundation' and created via NSConcreteMutableData initWithCapacity. During HTTP upload I'm creating a post body using NSMutableData, so I'm guessing these are buffers Cocoa is caching for me when I create the NSMutableData objects.

Is there a way to force Cocoa to free these? I'm 90% positive I'm releasing correctly (and Instruments and MallocDebug seem to confirm this), but I think Cocoa is keeping these around for perf reasons since I'm allocating so many MSMutableData buffers.