You’ll notice that this visual indicator is showing you total resident memory. Total resident memory refers to how much of your application’s memory resides in the device’s physical memory hardware (RAM). This is the clearest indicator of how demanding your application’s current memory usage is on the target device for two reasons. First, this is because as your application’s total resident memory usage increases, so does the likelihood of incurring frequent page faults, where the operating system has to page virtual memory in and out of the device’s physical memory. Frequent page faults will cause significant performance degradation of your application. And second, this is because many operating systems use your application’s resident memory usage to determine its current memory footprint. If your application’s memory footprint gets too high, the operating system will evict your application and terminate it, causing a crash for your players.
Therefore, you can use the Memory Usage On Device visual indicator in the Memory Profiler to infer if an application might be at risk of performance issues or being terminated by the operating system, due to an overuse of memory at the time of capture.
This contrasts with Allocated Memory, sometimes referred to as Committed Memory, which you might notice is displayed in various graphics below this indicator, and is currently the default option shown by all other views, such as Unity Objects. Allocated Memory refers to all memory that your application currently has allocated, regardless of whether it has been made resident in physical memory or not, and therefore it matches your application’s view of memory more closely. As such, this can be useful for exploring all of your application’s currently allocated memory, whilst resident memory usage is key to understanding the memory pressure your application is placing on the hardware at any moment in time.
Source: Unity Technologies Blog