On Fri, Nov 26, 2010 at 7:19 PM, Freddie Cash <fjwcash@xxxxxxxxx> wrote: > Within 2 weeks of booting, the host machine is using 2 GB of swap, and > disk I/O wait is through the roof. Restarting all of the VMs will > free up RAM, but restarting the whole box is the only way to get > performance back up. > > A guest configured to use 8 GB of RAM will have 9 GB virt and 7.5 GB > res shown in top. In fact, every single VM shows virt above the limit > set for the VM. Usually by close to 25%. Not sure about specific known issues with those Debian package versions, but... Virtual memory does not mean much. For example, a 64-bit process can map in 32 GB and never touch it. The virt number will be >32 GB but actually no RAM is being used. Or it could be a memory mapped file, which is backed by the disk and can pages can dropped if physical memory runs low. Looking at the virtual memory figure is not that useful. Also remember that qemu-kvm itself requires memory to perform the device emulation and virtualization. If you have an 8 GB VM, plan for more than 8 GB to be used. Clearly this memory overhead should be kept low, is your 25% virtual memory overhead figure from a small VM because 9 GB virtual / 8 GB VM is 12.5% not 25%? What is the sum of all VMs' RAM? I'm guessing you may have overcommitted resources (e.g. 2 x 8 GB VM on a 16 GB machine). If you don't leave host Linux system some resources you will get bad VM performance. Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
