Re: [Engine-devel] Question about hasMemoryToRunVM() in RunVmCommandBase

From: "ly pan" <plysab(a)gmail.com&gt; To: "Doron Fediuck" <dfediuck(a)redhat.com&gt; Cc: engine-devel(a)ovirt.org Sent: Wednesday, October 31, 2012 12:32:48 PM Subject: Re: [Engine-devel] Question about hasMemoryToRunVM() in RunVmCommandBase Hi Doron, Sorry for the so late reply. These days I looked into the code again and found it's my setting not rightly configured. 1. You opinion about reserved_mem is right. 2. Yes, pending_vmem_size is 0 before the 84th runs. 3. memory_over_commit is where my problem is. In webadmin UI, I set the cluster's memory optimization to none, thus memory_over_commit is 100 in DB(the dafault value is 100 in my env). when I set the cluster's mem_opt to 'for server load', memory_over_commit grows to 150 and when I set to 'for desktop load', memory_over_commit grows to 200. Both 'for server load' and 'for desktop load' have let the vdsMemLimit grows dramaticaly, thus the 84th vm managed to run. So I realized the memory optimization option in cluster is for KSM function. Thank you. ly pan 2012/10/24 Doron Fediuck <dfediuck(a)redhat.com&gt;: > ----- Original Message ----- >> From: "ly pan" <plysab(a)gmail.com&gt; >> To: engine-devel(a)ovirt.org >> Sent: Thursday, October 18, 2012 2:43:35 PM >> Subject: [Engine-devel] Question about hasMemoryToRunVM() in >> RunVmCommandBase >> >> 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. > > Hi Ly, > Sorry for the delay. I'd like to look into this issue. > In the meanwhile a few relevant points; > > 1. You're saying that reserved_mem=256. This is not accurate, since > it's > reported by vds as host_mem_reserve(256) + extra_mem_reserve(65) = > 321 > > 2. I'm assuming you retried running the 84th vm, just to make sure > your > pending_vmem_size is 0 once all 83 VMs are running. > > 3. So assuming (2) is correct, I'd like to ask what's the > max_vds_memory_over_commit > you have for the cluster? By default it's set to 120, and in such a > case the 84th > VM should still be running. > > Here's a calculation sample based on your data, and the above 3 > issues: > > vdsCurrentMem = > 83 * (512M+65) = 47,891 > 0 > 65 > 321 > 1 > ======= > 48,278 > > vdsMemLimit = > 120/100 > * > 47,321.1328125 // reported by vdsm: 'cat /proc/meminfo | grep > MemTotal' / 1024 > ========= > 56,785.359375 > > So vdsCurrentMem <= vdsMemLimit should be true unless you changed > something > such as the MemTotal or the memory_over_commit. You can try and > change memory_over_commit > let us know how it works. > > Doron _______________________________________________ Engine-devel mailing list Engine-devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel