Extreme Memory Oversubscription For VMs

Laxitive writes "Virtualization systems currently have a pretty easy time oversubscribing CPUs (running lots of VMs on a few CPUs), but have had a very hard time oversubscribing memory. GridCentric, a virtualization startup, just posted on their blog a video demoing the creation of 16 one-gigabyte desktop VMs (running X) on a computer with just 5 gigs of RAM. The blog post includes a good explanation of how this is accomplished, along with a description of how it's different from the major approaches being used today (memory ballooning, VMWare's page sharing, etc.). Their method is based on a combination of lightweight VM cloning (sort of like fork() for VMs) and on-demand paging. Seems like the 'other half' of resource oversubscription for VMs might finally be here."

Comments

Re:Kernel shared memory

[descubes]

Having written VM software myself (HP Integrity VM), I find this fascinating. Congratulations for a very interesting approach.

That being said, I'm sort of curious how well that would work with any amount of I/O happening. If you have some DMA transfer in progress to one of the pages, you can't just snapshot the memory until the DMA completes, can you? Consider a disk transfer from a SAN. With high traffic, you may be talking about seconds, not milliseconds, no?