"HugePages" is a feature integrated into the Linux kernel. It is a method to have larger page size that is useful for working with very large memory. There are couple of important benefits of HugePages.
* First, the "real" page size increases to 2MB, 50 times larger than the old 4KB page sizes.
* Pages that are used as huge pages are reserved inside the kernel and cannot be used for other purposes. Huge pages cannot be swapped out under memory pressure.
* With HugePages, the operating system page table (virtual memory to physical memory mapping) is smaller, since each page table entry is pointing to 2MB pages. This means less bookkeeping work for the kernel for that part of virtual memory due to larger page sizes.
Without HugePages, the operating system keeps each 4KB of memory as a page. When it is allocated to the SGA the lifecycle of that page (dirty, free, mapped to a process, and so on) is kept up to date by the operating system kernel.
-shmsegsize and HugePages are unrelated.
