Thoughts on Linux, Oracle, and VLM
From: Andrew Kerber <andrew.kerber_at_gmail.com>
Date: Tue, 17 Apr 2012 11:11:58 -0500
Message-ID: <CAJvnOJbro=wts9kbFLz=tBuJttqF5qVQkttZcvz80rOk4kcZvw_at_mail.gmail.com>
This question came up from a reader of my blog. She asks how high can we set vm.nr_hugepages. My response is below. Does anyone else have input on how much memory Linux actually needs on VLM systems: vm.nr_hugepages can be set to as much memory as available on the system. However, my general rule of thumb is that on Linux, oracle can use up to 80% of the total system memory, so take 80% of the total memory, subtract the amount of memory you want for the PGA_AGGREGATE_TARGET, and that tells you how much memory you can give to hugepages. One caveat is that I have not experimented with determining if there is an upper limit to how much memory the Linux OS needs. So on VLM systems, it is entirely possible the required OS memory number may be some fixed amount as opposed to 20% of the total system memory. eg, on 256G RAM system, its very possible that Linux needs a flat 25G instead of the 50G or so that my 80% rule of thumb suggests. Do any Linux experts have input?
Date: Tue, 17 Apr 2012 11:11:58 -0500
Message-ID: <CAJvnOJbro=wts9kbFLz=tBuJttqF5qVQkttZcvz80rOk4kcZvw_at_mail.gmail.com>
This question came up from a reader of my blog. She asks how high can we set vm.nr_hugepages. My response is below. Does anyone else have input on how much memory Linux actually needs on VLM systems: vm.nr_hugepages can be set to as much memory as available on the system. However, my general rule of thumb is that on Linux, oracle can use up to 80% of the total system memory, so take 80% of the total memory, subtract the amount of memory you want for the PGA_AGGREGATE_TARGET, and that tells you how much memory you can give to hugepages. One caveat is that I have not experimented with determining if there is an upper limit to how much memory the Linux OS needs. So on VLM systems, it is entirely possible the required OS memory number may be some fixed amount as opposed to 20% of the total system memory. eg, on 256G RAM system, its very possible that Linux needs a flat 25G instead of the 50G or so that my 80% rule of thumb suggests. Do any Linux experts have input?
-- Andrew W. Kerber 'If at first you dont succeed, dont take up skydiving.' -- http://www.freelists.org/webpage/oracle-lReceived on Tue Apr 17 2012 - 11:11:58 CDT