Windows has a "system managed size" option for pagefile size, which seems to lack precise documentation.
What exactly does Windows do when you choose this?
Does it simply select default min and max sizes, or does it do something fancier?
Does windows shrink the pagefile and grow it later (with annoying dialogs)?
Best Answer
It does exactly what it says on the tin: the OS manages the size of the pagefile, which can shrink or grow dynamically. The lower and upper bounds are 1x your RAM size and 3x your RAM size or 4 GB (whichever is larger) as explained more elaborately here. The pro is that you don't have to worry about sizing your pagefile, the con is that your pagefile can become fragmented.
Where it is useful is in exactly the situation it's designed to avoid: sizing your pagefile. You can set it to System Managed and check in every several minutes (via a script), recording the smallest and largest sizes it uses over a typical usage period of a month or so. You should then have a very good idea how large to manually set your pagefile to be.