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--- start:virtualization [2022/05/21 02:34] – peter
+++ start:virtualization [2023/09/14 20:18] (current) – peter
@@ Line 1: / Line 1: @@
+DATE CHECKED THIS PAGE WAS VALID: 14/09/2023
 So there is quite a bit to do when setting up for KVM.
 In the [[Start:ZramSwap| How To Setup Zramswap And Make Your PC Awesome]] we touch on setting up zram so that you can get more VM's but there is actually a way to get even better performance that I did not mention in that guide.
@@ Line 95: / Line 97: @@
 On my system a value of 4096 is 16 megabytes every cycle or 800MB a second (4096*4/1024 = 16 and the default sleep is every 20 milliseconds or 50 times a second). Thus every minute 46GB is being scanned and deduplicated if possible.
-On a modern system with lots of RAM getting through all the RAM in around 15 minutes would be good, so that you are checking the RAM can be optimized again and again. As its not uncommon for systems with around 256GB of RAM these days this value seems fairly reasonable to me at this time. Mine is probably a little high but the final optimization I leave to you, try aim to keep CPU under 40% and the amount of time around 15 minutes or so. That way when you fire up a VM, 15 minutes later some of the RAM can be claimed back. Setting this value too high is detrimental so try experiment to find the lowest value that is reasonable. There is no point scanning so quickly that everything is done every minute for example, try think of a reasonable goal like getting through the RAM in 15 minutes and work to find the lowest value that hits that. My test value above is high and not something I would use unless I was testing to see what I saved quickly just to benchmark if it was worth it at all.
+On a modern system with lots of RAM getting through all the RAM in around 15 minutes would be good, so that you are checking the RAM can be optimized again and again. As its not uncommon for systems with around 256GB of RAM these days this value seems fairly reasonable to me at this time. Mine is probably a little high but the final optimization I leave to you, try aim to keep CPU under 40% and the amount of time around 15 minutes or so. That way when you fire up a VM, 15 minutes later some of the RAM can be claimed back. Setting this value too high is detrimental so try experiment to find the lowest value that is reasonable. There is no point scanning so quickly that everything is done every minute for example, try think of a reasonable goal like getting through the RAM in 15 minutes and work to find the lowest value that hits that. My test value above is high and not something I would use unless I was testing to see what I saved quickly just to benchmark if it was worth it at all. Also not my system I was testing on was a desktop not a server. As mentioned a server would want a low value of CPU consumed like 10% or under. Setting this value high is detrimental to performance in terms of CPU so on a server where you can take a long time and let it optimize over many hours there is no benefit to an aggressive value.
 Here is htop showing the CPU being taxed:
@@ Line 252: / Line 254: @@
 === Notes ===
-Any further notes you can add here.
+Any VM with the following in the XML will not use the ksmd optimizations:
+  <memoryBacking>
+    <nosharepages/>
+  </memoryBacking>
+Adding that can exclude certain VM's from being memory optimized.
+For guest VM's dont forget to install the guest additions on the VM. In windows guet VMs you have to download them but on linux guests you can install them by:
+<code>
+sudo apt-get install qemu-guest-agent spice-vdagent
+</code>
+If you dont install them the guests tend to run sub optimally and slower.
+=== Notes ===
+Notes:
+Suggested value for pages to scan is:
+echo 1024 > /sys/kernel/mm/ksm/pages_to_scan
+Works well most systems.

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