iOS not always calling didReceiveMemoryWarning

I'm looking for help with a very specific memory-management issue where didReceiveMemoryWarning doesn't appear to be getting called in cases where it should be.

I have a straightforward app that's a story with pages. I have an outer view/controller that manages the page views/controller. Each page view has a picture on it of decent size (200-300k). It's large because it's a universal app, so they're all 1024x768, then get scaled down for the iPhone. I have implemented didReceiveMemoryWarning to release unused controllers (whatever's not showing at the time). The app works fine when didReceiveMemoryWarning gets called, but it does not always get called. On the iPod Touch 2G, if I'm going from page to page fast, it will often just kill the program without calling didReceiveMemoryWarning (I put a breakpoint there to see). On an iPhone 1G which has the same amount of RAM, didReceiveMemoryWarning gets called at reasonable times and I never run out of memory.

The log prints "Received memory warning level 1/2" as expected right before my code does get called, but I don't see it in the logs in the iPod Touch 2G when my app gets killed without a chance to free up memory.

I've used static analysis and the leaks tool and the memory profile looks good. I don't think leaks have anything to do with the problem. Rather, the problem is that my program doesn't get the oppo开发者_C百科rtunity to free up resources when memory is tight. I do want to keep unseen pages in memory when there's enough memory - it allows for quick paging and makes the pan gesture for changing pages work responsively.

Has anyone else seen this? If anyone has hints, I'd appreciate it. I'm also curious if anyone knows under what conditions didReceiveMemoryWarning should get called. Is it possible that my program is gobbling up so much memory so fast that iOS doesn't have an opportunity to free up memory?

Memory warnings appear to come too late when allocating a lot of memory "too" quickly, especially if the app doesn't spend enough idle time in the run loop between allocations.

Try preflighting (attempt to allocate and then release) memory, and return to the run loop, maybe a half second before you really need the memory.