Hi: This is my test environment: hardware: Dell PowerEdge 2710 ,Memory 48G Software: OVirt engine 3.0 ,VDSM 4.9.4 ,kernel 2.6.32-279.2.1.el6.x86_64 I create 100 vms from pool(each vm has 512M memory and has 1M memory garanteed, with guest_overhead = 65 and reserved_mem = 256), but only 83 vms turn out to run. When I run the 84th vm, engine says there is not enough memory. However at this time KSM is enabled and 15G free memory is still left on the host. I checked the code and found out that before running a vm, the function hasMemoryToRunVM() in RunVmCommandBase would decide whether there is enough memory in the selected host to run it. The Algorithm in the function is like this: mem_avaliable >= mem_required = curVds.getmem_commited() + curVds.getpending_vmem_size() + curVds.getguest_overhead() + curVds.getreserved_mem() + vm.getMinAllocatedMem(); And here is my question: curVds.getmem_commited() is caculated from the memory of vm assigned by user. But when the host is running with KSM enabled, the actual memory of each running vm would be smaller than the memory the user assigned to. In this case, the following may occur: engine says there be no more memroy to run any vm while the host has much free space to run more vms(in my case, 15G). Therefore I think the actual memory size reported by vdsm(The KSM shared memory) should be taken into account when calculating curVds.getmem_commited(). Any ideas are welcome.