Chapter 3. Configure Page Memory

A memory page is a fixed size, continuous block of memory and is used when transferring data from one storage medium to another, and to allocate memory. In some architectures, larger sized pages are available for improved memory allocation. These pages are known as large (or huge) pages.

The default memory page size in most operating systems is 4 kilobytes (kb). For a 32-bit operating system the maximum amount of memory is 4 GB, which equates to 1,048,576 memory pages. A 64-bit operating system can address 18 Exabytes of memory (in theory), resulting in a very large number of memory pages. The overhead of managing such a large number of memory pages is significant, regardless of the operating system.

Large memory pages are pages of memory which are significantly larger than 4 kb (usually 2 Mb). In some instances it is configurable from 2 MB to 2 GB, depending on the CPU architecture.

Large memory pages are locked in memory, and cannot be swapped to disk like normal memory pages. The advantage for this is if the heap is using large page memory it can not be paged or swapped to disk so it is always readily available. For Linux, the disadvantage is that applications must attach to it using the correct flag for the shmget() system call. Additionally, the proper security permissions are required for the memlock() system call. For any application that does not have the ability to use large page memory, the server behaves as if the large page memory does not exist, which can be a problem.

For additional information on page size refer to the Red Hat Enterprise Linux Configuring Hugetlb Huge Pages.