A large number of page ins may be a symptom of a large number of recent page outs.
To find out what process is reading these pages in, check the resident size of the processes you are running, and see which ones are increasing in size.
A large number of page ins may also occur when a large process has just stopped, and the kernel decides to fill that space with memory pages owned by other processes. Make sure that an important process hasn’t died unexpectedly.