On 04/30/2010 04:45 AM, Dave Hansen wrote:
A large portion of CMM2's gain came from the fact that you could take memory away from guests without _them_ doing any work. If the system is experiencing a load spike, you increase load even more by making the guests swap. If you can just take some of their memory away, you can smooth that spike out. CMM2 and frontswap do that. The guests explicitly give up page contents that the hypervisor does not have to first consult with the guest before discarding.
Frontswap does not do this. Once a page has been frontswapped, the host is committed to retaining it until the guest releases it. It's really not very different from a synchronous swap device.
I think cleancache allows the hypervisor to drop pages without the guest's immediate knowledge, but I'm not sure.
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