获取 iOS APP 内存占用的大小

当我们想去获取 iOS 应用的占用内存时，通常我们能找到的方法是这样的，用 resident_size：

 

#import <mach/mach.h>
- (int64_t)memoryUsage {
    int64_t memoryUsageInByte = 0;
    struct task_basic_info taskBasicInfo;
    mach_msg_type_number_t size = sizeof(taskBasicInfo);
    kern_return_t kernelReturn = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t) &taskBasicInfo, &size);
    
    if(kernelReturn == KERN_SUCCESS) {
        memoryUsageInByte = (int64_t) taskBasicInfo.resident_size;
        NSLog(@"Memory in use (in bytes): %lld", memoryUsageInByte);
    } else {
        NSLog(@"Error with task_info(): %s", mach_error_string(kernelReturn));
    }
    
    return memoryUsageInByte;
}

但是测试的时候，我们会发现这个跟我们在 Instruments 里面看到的内存大小不一样，有时候甚至差别很大。

更加准确的方式应该是用 phys_footprint：

 

#import <mach/mach.h>
- (int64_t)memoryUsage {
    int64_t memoryUsageInByte = 0;
    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) {
        memoryUsageInByte = (int64_t) vmInfo.phys_footprint;
        NSLog(@"Memory in use (in bytes): %lld", memoryUsageInByte);
    } else {
        NSLog(@"Error with task_info(): %s", mach_error_string(kernelReturn));
    }
    return memoryUsageInByte;
}

关于 phys_footprint 的定义可以在 XNU 源码中，找到 osfmk/kern/task.c 里对于 phys_footprint 的注释：

 

/*
 * phys_footprint
 *   Physical footprint: This is the sum of:
 *     + (internal - alternate_accounting)
 *     + (internal_compressed - alternate_accounting_compressed)
 *     + iokit_mapped
 *     + purgeable_nonvolatile
 *     + purgeable_nonvolatile_compressed
 *     + page_table
 *
 * internal
 *   The task's anonymous memory, which on iOS is always resident.
 *
 * internal_compressed
 *   Amount of this task's internal memory which is held by the compressor.
 *   Such memory is no longer actually resident for the task [i.e., resident in its pmap],
 *   and could be either decompressed back into memory, or paged out to storage, depending
 *   on our implementation.
 *
 * iokit_mapped
 *   IOKit mappings: The total size of all IOKit mappings in this task, regardless of
     clean/dirty or internal/external state].
 *
 * alternate_accounting
 *   The number of internal dirty pages which are part of IOKit mappings. By definition, these pages
 *   are counted in both internal *and* iokit_mapped, so we must subtract them from the total to avoid
 *   double counting.
 */

注释里提到的公式计算的应该才是应用实际使用的物理内存。

转载自新浪博客