Hello Neil,
You also have contiguous memory allocation and it can’t be swapped.
Neil Chandler <neil_chandler@xxxxxxxxxxx> hat am 22. Februar 2018 um 09:47--
geschrieben:
Transparent Hugepages should be disabled, to prevent the Kernel “helping you
out” and causing CPU spikes and unpredictable performance hits.
You should always be using Hugepages.
They give a minor performance improvement and a significant memory saving in
terms of the amount of memory needed to handle the pages - less Transaction
Lookaside Buffers, which also means less TLB misses (which are expensive).
You are handling the memory chopped up into 2MB pieces instead of 4K. But you
also have a single shared memory TLB for Hugepages.
The kernel has less work to do, bookkeeping fewer pointers in the TLB.
You also have contiguous memory allocation and it can’t be swapped.
If you are having problems with Hugepages, you have probably overallocated
them (I’ve seen this several times at clients so it’s not uncommon).
Hugepages can *only* by used for your SGA’s. All of your SGA’s should fit
into the Hugepages and that should generally be no more than about 60% of the
total server memory (but there are exceptions), leaving plenty of “normal”
memory (small pages) for PGA , O/S and other stuff like monitoring agendas.
As an added bonus, AMM can’t use Hugepages, so your are forced to use ASMM.
AMM doesn’t work well and has been kind-of deprecated by oracle anyway - dbca
won’t let you setup AMM if the server has more than 4GB of memory.
Neil.
sent from my phone
