Large Pages Huge Pages
Posted on 2014-07-29
When the database starts up the alert log writes
Total System Global Area size is 12 GB. For optimal performance,
prior to the next instance restart:
1. Increase the number of unused large pages by
at least 6145 (page size 2048 KB, total size 12 GB) system wide to
get 100% of the System Global Area allocated with large pages
2. Large pages are automatically locked into physical memory.
Increase the per process memlock (soft) limit to at least 12 GB to lock
100% System Global Area's large pages into physical memory"
Today I'm seeing in an article
"Understanding Hugepages in Oracle Database
By David Fitzjarrell
Recently I've noticed the occasional thread in Oracle newsgroups and lists asking about hugepages support in Linux, including 'best practices' for hugepages configuration. This information is out on the 'world-wide web' in various places; I'd rather put a lot of that information in this article to provide an easier way to get to it. I'll cover what hugepages are, what they do, what they can't do and how best to allocate them for your particular installation. Let's get started.
"Normal" memory pages in Linux are 4 KB in size and are allocated as needed where the memory map will allow so they are likely not contiguous. Hugepages, in comparison, are 2 MB pages locked in memory and are allocated in a contiguous 'chunk'; these are allocated at boot time using a parameter in the /etc/sysctl.conf file named vm.nr_hugepages for RedHat Linux kernel 2.6 and a parameter named vm.hugetlb_pool for RedHat Linux kernel 2.4. You must remember that each page is 2 MB is size, as this affects how many hugepages you need to allocate to cover all of the SGAs of running Oracle databases.
Are these hugepages referred to in this article the same as hugepages in my alert log??