FBMemoryProfile won't match XCode Debug gauges

[kojiyijian]

Use Unity build a game App. when the unity scene unloaded the xcode memory from 400M drop to 200m, but the FBMemoryProfile still around 400M.
I also use the mach_task_basic_info and host_statistics API, it also dose't match the XCode Debug gagues, is there any other solution to get Ram usage by the App on IOS?