I think mongo won't start in lxc without overcommit sysctl

Yea probably skimmed the 900p being nearly the best swap device out there. I also had a quick graph with a 850 evo as well, and while it was worse, it wasn't that much worse. The effect of ram on caching is interesting and I have some ideas for scripts to test different caching systems, but its hard to test caching is all about trying to predict user workloads, and it can be hard to get consistent numbers that are applicable to the real world.

Thanks for the idea. I should look more into KSM sharing and when/how it works.

Like as a boot drive? Sure you can use that for the boot drive for the VM with a bit of configuration. In general RAM drives aren't worth it for VM boot, but I can make a video looking into it if your interested.

As far as the Proxmox services getting killed by OOM, It looks like linux has a score that the OOM uses to determine what to kill first, and from a quick look at a system the vms would get killed before all the proxmox services from my quick look. I agree my zram tests were flawed, but the issue is snappyness is hard to measure well. Let me know if you know a good way to measure snappyness and I'll give it a run, but since I couldn't really think of a better test I stuck with the ffmpeg encode. I'm sure zram has its uses as its the default on many distros.

11:42 I would not recommend a low swappiness setting and waiting for swap being used, keep it higher, because you are reducing performance because you loose things like file system cache.

My mindset was that a low swappyness will be best if you normally have enough RAM, and want to make sure there aren't performance hits if a part of a VM gets swapped out and then needed later on. The swap would then keep the OOM killer from taking out VMs, and be an indicator if more RAM is needed. If you plan on using swap, then a higher swappiness value would be better as its proactively swapping out unused ram instead of waiting for ram usage to be high. This really depends on the usecase of the system and VMs. I often seen Proxmox servers where RAM usage isn't that high, so my thought was avoid performance hits by having parts of VMs in swap and the smaller disk cache shoudn't hurt performance that much, but again really depends on the use case. Hope this explains some of my thoughts in the video.

@@ElectronicsWizardry "If you plan on using swap, then a lower swappiness value would be better" OK, agree. I guess I should have thought about the title of the video again. 🙂

Oops that should have been higher value to proactively swap out ram. I edited the earlier comment.

I'd check that 500 swappiness value. I think swappiness should max out at 200. And larger values typically mean swap will be used more. I'm curious how big you have your ARC set to.

@@ElectronicsWizardry *edit* I stand corrected. I just checked my system (couldn't do it earlier whilst I was at work). Swappiness is set to 10 on my main Proxmox "do it all" server. It was vm.vfs_cache_pressure that I have set to 500. "vfs_cache_pressure This percentage value controls the tendency of the kernel to reclaim the memory which is used for caching of directory and inode objects. At the default value of vfs_cache_pressure=100 the kernel will attempt to reclaim dentries and inodes at a “fair” rate with respect to pagecache and swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will never reclaim dentries and inodes due to memory pressure and this can easily lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 causes the kernel to prefer to reclaim dentries and inodes. Increasing vfs_cache_pressure significantly beyond 100 may have negative performance impact. Reclaim code needs to take various locks to find freeable directory and inode objects. With vfs_cache_pressure=1000, it will look for ten times more freeable objects than there are." (Source: www.kernel.org/doc/html/v5.4/admin-guide/sysctl/vm.html) Either way, even with a vm.swappiness=10, my system still swaps out like crazy despite the fact that I have 56 GB of RAM free.