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I have a universal app that is essentially a list of articles with images and text, and menu under the left side of the app. I have google analytics in, as well as parse's framework.

The only difference between the app on the iPad and iPhone is that the side menu is always visible on the ipad, and a few interface objects are moved around. (different cell layout for the list--same content, though).

The images are loaded asynchronously using a set of classes that I wrote to download/save in an NSCache object and on the disk using a NSOperationQueue. (disk cache is wiped when the user leaves the app). The NSCache is set to max out at roughly 10 mb. (assuming image size is image hight*image width * 4 bytes per image). (code here is identical for both, so it shouldn't be the culprit, but it is a large chunk of the apps memory use).

I was having some trouble with memory warnings/crashing on an older iphone4 running iOS 5.0, so I ran the app with the Activity Monitor Instrument, and noticed something very odd:

On the iPad (an iPad 2 running iOS 5.1) the app launched, loaded the images that were visible immediately, and was using about 16mb of memory.

On the iPhone4 it launched, loaded the visible images and was using about 35mb of memory--way more than I would expect.

In order to check if it was an OS memory issue, I also ran the app on an iPhone5 running iOS6 and it used about the same amount as the iPhone 4.

I checked my media and the storyboard files to see if anything was different at all, and I could not find anything that could change the memory usage in any significant way.

Is there any way to reduce the memory use of the app on the iphone? I can think of no reason it would use so much memory.

Nyth
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    The other answers here are good guesses, but to see where the memory is allocated, you need to use the **Allocations** instrument, not the **Activity Monitor** instrument. Select "Call Tree", and make sure you have "Show Obj-C Only" and "Hide System Calls" checked. – Aaron Brager Jun 13 '13 at 22:30
  • it's very hard to guess whats going on based on the information given here, but have you taken the retina display of iPhone 4 and 5 into account? Remember that retina requires double image sizes to look correct... – EsbenB Jun 13 '13 at 22:26
  • Perhaps the following affects your problem. The iPad 2 is not a Retina device, but the iPhone4 is. That means that textures loaded may take up to 4 times the memory. – Rob van der Veer Jun 13 '13 at 22:23

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Very difficult to see.. as one person stated pay attention that retina devices will use more memory according to the source, if in the bundle you set @2x images it will load them, and they use more memory. Have tried to profile the Virtual memory using allocations? Using memory is usually fine even if it fires a memory warning, the problem is how you respond to it, when it comes does it free enough memory? try with the simulator to simulate a memory warning. Pay attention that sim uses more memory than device. One other point is that since ARC is difficult to create leaks, but it's easier to create retain cycle and abandoned memory. A correct object life cycle should end with object deallocation. You say that you use NSCache and load images from the net async, I've got 3 suggestion for you :

  1. Do you know the original image size on the source? maybe on the iPad source images are smaller than on iPhone. A correct approach after you download an image will be resize it according to the really needed size (I'm mean redrawing non just stretching) you ca achieve that with Quartz or using ImageIO
  2. I never understood the behaviour of NSCache after memory warning, Apple says that it will flush the memory but after some test on iOS4 (I don't know now) I don't agree. I've created my own subclass that observe for memory warning and flushes memory
  3. Are you totally sure that you are getting back image from the cache ?
Andrea
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  • I am definitely resizing the images when they're downloaded, prior to putting them in the cache, and images are definitely being returned from the cache. They're also the same images on both devices. While retina displays do use more memory as a result of larger images, the ipad screen resolution is still larger than the iphone 4, and the interface images wouldn't account for 30mb of memory, would they? – Nyth Jun 14 '13 at 17:37
  • Well that's weird, check with instruments for leaks and retain cycles, use also the VMTracker, is not a normal behavior – Andrea Jun 14 '13 at 18:58