IOS Ram resident set size

This is a pretty interesting video

I am really curious about this part of the video

The way iOS is able to shrink the amount of resident set size of the application when it moves into the background.

The guy doesn't know how it's done and neither do I. Anyone here have any idea how they could be implementing something like that?

It would seem paging isn't it because like he said earlier in the video, constantly paging data on flash memory can wear out the memory really quick.

Any ideas how iOS is doing this memory magic?