Distinguishing Between Short Term and Long Term Pins of Pages in Virtual Memory During I/O
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
By distinguishing between "Short Term" pins, where a page in virtual memory will be unpinned after the I/O completes, and "Long Term" pins, where the page may or may not be unpinned ever, it is possible to prevent a process, or several processes, from pinning all of real memory and deadlocking the system. In a Virtual Storage environment supported by demand paging, when it is necessary for an I/O device to write or read a particular page in virtual memory, it is necessary to "Pin" that page in memory. This prevents the page replacement mechanism from paging the page out. Most I/O devices require a page to be resident while it is being accessed in order to function properly. There are other reasons to pin pages in the system, e.g., to improve performance in certain critical paths.