Get amount of memory used by app in iOS

I'm working on an upload app that splits files before upload. It splits the files to prevent being closed by iOS for using too much memory as some of the files can be rather large. It would be great if I could, instead of setting the max "chunk" size, set the max memory usage and determine the size using that.

Something like this

    #define MAX_MEM_USAGE 20000000 //20MB
    #define MIN_CHUNK_SIZE 5000   //5KB

    -(void)uploadAsset:(ALAsset*)asset
    {
        long totalBytesRead = 0;
        ALAssetRepresentation *representation = [asset defaultRepresentation];
        while(totalBytesRead < [representation size])
        {
            long chunkSize = MAX_MEM_USAGE - [self getCurrentMemUsage];
            chunkSize = max(chunkSize,MIN_CHUNK_SIZE);//if I can't get 5KB without getting killed then I'm going to get killed
            uint8_t *buffer = malloc(chunkSize);
            //read file chunk in here, adding the result to totalBytesRead
            //upload chunk here
        }
    }

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Is essentially what I'm going for. I can't seem to find a way to get the current memory usage of my app specifically. I don't really care about the amount of system memory left.

The only way I've been able to think of is one I don't like much. Grab the amount of system memory on the first line of main in my app, then store it in a static variable in a globals class then the getCurrentMemUsage would go something like this

    -(long)getCurrentMemUsage
    {
        long sysUsage = [self getSystemMemoryUsed];
        return sysUsage - [Globals origSysUsage];
    }

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This has some serious drawbacks. The most obvious one to me is that another app might get killed in the middle of my upload, which could drop sysUsage lower than origSysUsage resulting in a negative number even if my app is using 10MB of memory which could result in my app using 40MB for a request rather than the maximum which is 20MB. I could always set it up so it clamps the value between MIN_CHUNK_SIZE and MAX_MEM_USAGE, but that would just be a workaround instead of an actual solution.

If there are any suggestions as to getting the amount of memory used by an app or even different methods for managing a dynamic chunk size I would appreciate either.
Curtis LongAsked:
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pgnatyukCommented:
Here is the code detecting the used memory:

#import <mach/mach.h> 
#import <mach/mach_host.h>

+ (NSUInteger)amountOfUsedMemory 
{
    struct task_basic_info info;
    mach_msg_type_number_t size = sizeof(info);
    kern_return_t kerr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&info, &size);
    return (kerr == KERN_SUCCESS) ? info.resident_size : 0;
}

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But I think, it's better to control the chunk size as you do it now.
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Curtis LongAuthor Commented:
Why would it be any better to use a static chunk size?
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pgnatyukCommented:
If the file size that you need to upload is less than the predefined chunk size? So it's never a static size.
Why you took 20MB? Maybe this number can be much smaller? 4MB, for example?
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