how XCode to calculate Memory

is there any public API or Method to get resident size of current process of game like Debug Gauges to Monitor Memory?

As far as i know someone use XCode instrument -> show the Debuger navigator -> Memory to get it, before i have found some API to get it

from internet,but a big differece bettween with the result of XCode Debuger navigator .

the first method like this:

    struct mach_task_basic_info info; 
    mach_msg_type_number_t      count = MACH_TASK_BASIC_INFO_COUNT; 

    if (task_info(mach_task_self(), MACH_TASK_BASIC_INFO, (task_info_t)& info, &count) == KERN_SUCCESS) 
    { 
       int32_t _pss = (int32_t)info.resident_size / (1024 * 1024); 
    }

another method like this:

    task_vm_info_data_t vmInfo;
    mach_msg_type_number_t count = TASK_VM_INFO_COUNT;
    kern_return_t kernelReturn = task_info(mach_task_self(), TASK_VM_INFO, (task_info_t) &vmInfo, &count);
    if(kernelReturn == KERN_SUCCESS)
    {
       int32_t _pss = (int32_t) vmInfo.phys_footprint / (1024 * 1024);
    }

someone discuss:https://github.com/aozhimin/iOS-Monitor-Platform/issues/5

a big differnece bettween the result of the first method and the result of XCode Debug navigator instrument, info.resident_size will not increase When the memory is allocated continuously,but xcode Debug navigator will increase.
but a little difference bettween the result of the second method and the result of XCode Debug navigator instrument when use game test,but application app will same with it.

so i want to know how XCode Debug navigator to calculate Memory or how to get resident size of current process more precise,any idea will help me,thanks in advance!