iOS ARC内存不断增加

Question

Here is my code. Memory has been constantly increasing,when the viewDidLoad method is called.I guess that local variable data is not released.But why?

- (void)viewDidLoad {
   [super viewDidLoad];

   NSData *data = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"wakeup.pcm" ofType:nil]];
NSMutableData *mData = [NSMutableData dataWithData:data];

  int readLength = 0;
  while (readLength < mData.length) {
     if (mData.length - readLength > EVERBUFFERLEN) {
        NSData *data = [mData subdataWithRange:NSMakeRange(readLength, EVERBUFFERLEN)];
        readLength += EVERBUFFERLEN;
        data = nil;
    }
}

Answer 1

Such a "overall memory meter" does not really help finding leaks. I. e. it can be that -dataWithContentsOfFile: requests memory down from the system, but it is not freed after usage. Reasons for that can be that allocating memory from the system is slow and holding unused memory "for the app" can be a cheaper way as long as the memory pressure isn't high.