Hi Paolo, Thank you for the answer. I suspect that overcommit thing. In my case it's a combination of unused memory and KSM.
So hugepages are not so useful as I saw in the presentations. I think it works just for some usecases. Thanks On Fri, Jul 31, 2015 at 12:54 AM, Paolo Bonzini <[email protected]> wrote: > > > On 31/07/2015 01:08, Pavel Shirshov wrote: >> Hello, >> >> Today I was very surprised to see that KVM with enabled HugePages uses >> much more memory versus KVM without HugePages enabled. >> >> I have a server with 386Gb memory. >> I have a VM image which allocate up to 3.2Gb memory (libvirt <memory/> tag). >> >> Without HugePages enabled on the server I can create up to 235 VM on the >> server. >> >> With HugePages enabled I can create about 105 VMs on the same server. >> I reserve 180000 2Mb pages on the server. >> >> I see that 180000*2Mb / 3.2 Gb = 112.5 VMs. >> >> How KVM without HugePages is able to create 235 VMs? Does KSM help? > > KVM without hugepages can overcommit. It can do this thanks to unused > memory (never touched by the VM, thus all zero), swapping out, > deduplication (KSM), ballooning or a combination of the four. > > Hugepages are never overcommitted. > > Paolo > >> Is it possible to tune KVM with HugePages up to support ~200 VMs? >> >> Thanks -- With best regards, Pavel S. Shirshov -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
