pagefile.sys is a file where you emulate ram on hard disk, the idea is never use that file, since it is very slow when compared to the ram on your system
ideally you should have a 16 gbs to up to 24 gbs of ram in size in it
the idea is have a 1 to 1.5 times bigger pagefile than the ram you have but it is not desirable because most people will see it as wasted hard disk space, a problem in a ssd with limmited size
you can leave it fixed determined by windows, auto to windows to inflate or deflate it as required or you put a value, i wouldn't put more than 16 gbs