Linux- AMM, ASMM, Hugepages , swappiness
Date: Mon, 9 Nov 2009 14:45:21 -0000
As we all know, AMM (Automatic Memory Management) feature of 11g is not compatible with use of HugePages on Linux. One could still use HugePages on Linux with 11g by disabling AMM, and enabling ASMM (Automatic Shared Memory Management) and automatic PGA memory management.
AMM is supported using tmpfs on /dev/shm. AMM is not compatible with ramfs on /dev/shm.
I would have thought that using hugepages has advantages over use of tmpfs on /dev/shm. As with hugepages, kernel has fewer PTE (page table entry) to maintain. And hugepage locked memory is locked into physical RAM and is never swapped to swap filesystem. So your SGA is never swapped during inactive period, thereby allowing quick ramp up due to sudden activity after a quiet period.
If using AMM, one can disable swap on Linux using following setting , which favours pages to be in RAM rather than swap file.
vm.swappiness = 0
Does anyone has any thoughts on which is better to use - (AMM with tmpfs + vm.swappiness=0 ) or (hugepages + ASMM + automatic PGA) ?