virtual-host: More aggressive writeback of dirty

[Red54]

vm.dirty_ratio of system default is 20, so set vm.dirty_ratio of virtual-host to 10.

RHEL 7: Virtualization Tuning and Optimization Guide: Chapter 4. tuned and tuned-adm:

Based on the throughput-performance profile, virtual-host also enables more aggressive writeback of dirty pages. This profile is the recommended profile for virtualization hosts, including both KVM and Red Hat Virtualization (RHV) hosts.

RHEL 8: Configuring and managing virtualization: Chapter 16. Optimizing virtual machine performance:

For RHEL 8 virtualization hosts, use the virtual-host profile. This enables more aggressive writeback of dirty memory pages, which benefits the host performance.

RHEL 9: Configuring and managing virtualization: Chapter 17. Optimizing virtual machine performance:

For RHEL 9 virtualization hosts, use the virtual-host profile. This enables more aggressive writeback of dirty memory pages, which benefits the host performance.

[yarda]

Thanks for the contribution and sorry for the delay. Do you have some benchmark data supporting this change? It's apparent that this needs a fix, but it could be also fixed in the documentation.