linux page-cache size (host) performance impact to Virtualbox VMs

i have a small Virtualisation host that runs 7 Windows 10 and CentOS VMS. The host has only 32GB RAM and that RAM is nearly used by the VMs memory and the linux host OS. There are about 2,5GB RAM left that are used by the linux host page cache.

I#m now asking myself if i can upgrade performance of the VMs by adding additional RAM that more RAM can be used by the page.cache to buffer read/write HD operations.

From my point it's the question if the Host OS is seeing only the vdi-files of the VMs (the virtual harddrives of the VMs) at a "whole" or if the host OS can see the single files the VMs-OSses are writting inside there vdi-virtual harddrives.

I searched for that but did not found any info. Can someone explain it to me please?

Thanks

Solution 1:

More RAM used for pagecache will surely have a beneficial effect on VMs performance - but evaluating by how much is the hard part, due to different workloads responding in different manner to increased cache.

For example, a completely random read workload (a very rare scenario) or a totally write-bound load (somewhat more likely, but again quite unusual) will see small or not benefit at all from the increased pagecache.

That said common, more mixed workloads are going to get a significant boost.