Hi , I Sent this to the wrong list (libvirt-devel) on friday ... so i am trying to send it to the correct one this time. Apologize for double posting. I also created a ticket on bugzilla.redhat.com for this https://bugzilla.redhat.com/show_bug.cgi?id=927336 still i am posting it here because is absolutely possible i am doing something wrong and someone here will see it . Description of the problem: When the virsh setmem command is used to inflate (or deflate) the balloon on a VM to which 8GB of MaxMemory or more are allocated then the information reported with virsh dominfo , virsh dumpxml after the balloon change has been performed are wrong. The actual balloon is inflated correctly though and that is verifiable both in the vm itself and through the "virsh dommemstat" commands. Platform is Centos 6.4 (problem was present in 6.3 as well starting with libvirt-0.9.10-21.el6.3.7 ) The patch that actually is causing the problem is patch number 398 in the src rpm for libvirt-0.9.10-21.el6.3.7 : libvirt-Wire-up-handling-for-QMP-s-BALLOON_EVENT.patch ( https://bugzilla.redhat.com/show_bug.cgi?id=884713) And i verified it by removing the patch and recompiling the rpm , that indeed worked perfectly after that. The problem exists in every version up to the latest (that is what i am running now) but now the patch is part of the libvirt source code in itself and not a patch in the rpm anymore. Software used: # yum list installed | egrep -i "qemu|libvirt" gpxe-roms-qemu.noarch 0.9.7-6.9.el6 @base libvirt.x86_64 0.10.2-18.el6_4.2 @updates libvirt-client.x86_64 0.10.2-18.el6_4.2 @updates libvirt-python.x86_64 0.10.2-18.el6_4.2 @updates qemu-img.x86_64 2:0.12.1.2-2.355.0.1.el6.centos.2 @updates qemu-kvm.x86_64 2:0.12.1.2-2.355.0.1.el6.centos.2 @updates qemu-kvm-tools.x86_64 2:0.12.1.2-2.355.0.1.el6.centos.2 @updates Full example ( long and include debug logs ) : 1) Start VM with 12GB of MAX and CURRENT (12582912) (tail -f libvirtd.log | grep -i balloon) 2013-03-22 21:06:34.438+0000: 23180: debug : qemuMonitorSetBalloon:1690 : mon=0x7f3d6c1789e0 newmem=12582912 2013-03-22 21:06:34.438+0000: 23180: debug : virJSONValueToString:1133 : result={"execute":"balloon","arguments":{"value":12884901888},"id":"libvirt-6"} 2013-03-22 21:06:34.438+0000: 23180: debug : qemuMonitorJSONCommandWithFd:265 : Send command '{"execute":"balloon","arguments":{"value":12884901888},"id":"libvirt-6"}' for write with FD -1 2013-03-22 21:06:34.438+0000: 23180: debug : qemuMonitorSend:903 : QEMU_MONITOR_SEND_MSG: mon=0x7f3d6c1789e0 msg={"execute":"balloon","arguments":{"value":12884901888},"id":"libvirt-6"} 2013-03-22 21:06:34.439+0000: 23179: debug : qemuMonitorIOWrite:461 : QEMU_MONITOR_IO_WRITE: mon=0x7f3d6c1789e0 buf={"execute":"balloon","arguments":{"value":12884901888},"id":"libvirt-6"} # dominfo 2 Id: 2 Name: centos_jt UUID: bc25a6c4-ba34-a593-47c7-6372999946d6 OS Type: hvm State: running CPU(s): 1 CPU time: 26.6s Max memory: 12582912 KiB Used memory: 12582912 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0 2) set mem to 8GB (Fail as described) # setmem 2 --live --config --size 8388608 2013-03-22 21:13:45.522+0000: 23183: debug : qemuMonitorSetBalloon:1690 : mon=0x7f3d6c1789e0 newmem=8388608 2013-03-22 21:13:45.522+0000: 23183: debug : virJSONValueToString:1133 : result={"execute":"balloon","arguments":{"value":8589934592 },"id":"libvirt-9"} 2013-03-22 21:13:45.522+0000: 23183: debug : qemuMonitorJSONCommandWithFd:265 : Send command '{"execute":"balloon","arguments":{"value":8589934592},"id":"libvirt-9"}' for write with FD -1 2013-03-22 21:13:45.522+0000: 23183: debug : qemuMonitorSend:903 : QEMU_MONITOR_SEND_MSG: mon=0x7f3d6c1789e0 msg={"execute":"balloon","arguments":{"value":8589934592},"id":"libvirt-9"} 2013-03-22 21:13:45.523+0000: 23179: debug : qemuMonitorIOWrite:461 : QEMU_MONITOR_IO_WRITE: mon=0x7f3d6c1789e0 buf={"execute":"balloon","arguments":{"value":8589934592},"id":"libvirt-9"} 2013-03-22 21:13:45.528+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d6c1789e0 buf={"timestamp": {"seconds": 1363986825, "microseconds": 528314}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:13:45.528+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363986825, "microseconds": 528314}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}}] 2013-03-22 21:13:45.528+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363986825, "microseconds": 528314}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:13:45.528+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d6c1789e0 event={"timestamp": {"seconds": 1363986825, "microseconds": 528314}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:13:45.528+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1685ce0 2013-03-22 21:13:45.528+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d6c1789e0 2013-03-22 21:13:45.528+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 12582912 to 12581888 kb 2013-03-22 21:13:46.528+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d6c1789e0 buf={"timestamp": {"seconds": 1363986826, "microseconds": 352941}, "event": "BALLOON_CHANGE", "data": {"actual": 12884901888}} 2013-03-22 21:13:46.528+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363986826, "microseconds": 352941}, "event": "BALLOON_CHANGE", "data": {"actual": 12884901888}}] 2013-03-22 21:13:46.528+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363986826, "microseconds": 352941}, "event": "BALLOON_CHANGE", "data": {"actual": 12884901888}} 2013-03-22 21:13:46.528+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d6c1789e0 event={"timestamp": {"seconds": 1363986826, "microseconds": 352941}, "event": "BALLOON_CHANGE", "data": {"actual": 12884901888}} 2013-03-22 21:13:46.528+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1686770 2013-03-22 21:13:46.528+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d6c1789e0 2013-03-22 21:13:46.528+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 12581888 to 12582912 kb virsh # dominfo 2 Id: 2 Name: centos_jt UUID: bc25a6c4-ba34-a593-47c7-6372999946d6 OS Type: hvm State: running CPU(s): 1 CPU time: 41.6s Max memory: 12582912 KiB Used memory: 12582912 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0 virsh # dommemstat 2 actual 8388608 rss 599916 The Balloon was actually inflated , and in the VM i can see 8GB of Ram available with free 3) setmem to to 3000000 (Fail as described) 2013-03-22 21:18:19.182+0000: 23181: debug : qemuMonitorSetBalloon:1690 : mon=0x7f3d6c1789e0 newmem=3000000 2013-03-22 21:18:19.182+0000: 23181: debug : virJSONValueToString:1133 : result={"execute":"balloon","arguments":{"value":3072000000 },"id":"libvirt-63"} 2013-03-22 21:18:19.182+0000: 23181: debug : qemuMonitorJSONCommandWithFd:265 : Send command '{"execute":"balloon","arguments":{"value":3072000000},"id":"libvirt-63"}' for write with FD -1 2013-03-22 21:18:19.182+0000: 23181: debug : qemuMonitorSend:903 : QEMU_MONITOR_SEND_MSG: mon=0x7f3d6c1789e0 msg={"execute":"balloon","arguments":{"value":3072000000},"id":"libvirt-63"} 2013-03-22 21:18:19.183+0000: 23179: debug : qemuMonitorIOWrite:461 : QEMU_MONITOR_IO_WRITE: mon=0x7f3d6c1789e0 buf={"execute":"balloon","arguments":{"value":3072000000},"id":"libvirt-63"} 2013-03-22 21:18:19.184+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d6c1789e0 buf={"timestamp": {"seconds": 1363987099, "microseconds": 184245}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:18:19.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363987099, "microseconds": 184245}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}}] 2013-03-22 21:18:19.184+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363987099, "microseconds": 184245}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:18:19.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d6c1789e0 event={"timestamp": {"seconds": 1363987099, "microseconds": 184245}, "event": "BALLOON_CHANGE", "data": {"actual": 12883853312}} 2013-03-22 21:18:19.184+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1688320 2013-03-22 21:18:19.184+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d6c1789e0 2013-03-22 21:18:19.191+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 12582912 to 12581888 kb 2013-03-22 21:18:20.184+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d6c1789e0 buf={"timestamp": {"seconds": 1363987100, "microseconds": 184128}, "event": "BALLOON_CHANGE", "data": {"actual": 11874074624}} 2013-03-22 21:18:20.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363987100, "microseconds": 184128}, "event": "BALLOON_CHANGE", "data": {"actual": 11874074624}}] 2013-03-22 21:18:20.184+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363987100, "microseconds": 184128}, "event": "BALLOON_CHANGE", "data": {"actual": 11874074624}} 2013-03-22 21:18:20.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d6c1789e0 event={"timestamp": {"seconds": 1363987100, "microseconds": 184128}, "event": "BALLOON_CHANGE", "data": {"actual": 11874074624}} 2013-03-22 21:18:20.184+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1685ce0 2013-03-22 21:18:20.184+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d6c1789e0 2013-03-22 21:18:20.184+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 12581888 to 11595776 kb 2013-03-22 21:18:21.184+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d6c1789e0 buf={"timestamp": {"seconds": 1363987100, "microseconds": 224930}, "event": "BALLOON_CHANGE", "data": {"actual": 11661934592}} 2013-03-22 21:18:21.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363987100, "microseconds": 224930}, "event": "BALLOON_CHANGE", "data": {"actual": 11661934592}}] 2013-03-22 21:18:21.184+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363987100, "microseconds": 224930}, "event": "BALLOON_CHANGE", "data": {"actual": 11661934592}} 2013-03-22 21:18:21.184+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d6c1789e0 event={"timestamp": {"seconds": 1363987100, "microseconds": 224930}, "event": "BALLOON_CHANGE", "data": {"actual": 11661934592}} 2013-03-22 21:18:21.184+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1686770 2013-03-22 21:18:21.184+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d6c1789e0 2013-03-22 21:18:21.184+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 11595776 to 11388608 virsh # dominfo 2 Id: 2 Name: centos_jt UUID: bc25a6c4-ba34-a593-47c7-6372999946d6 OS Type: hvm State: running CPU(s): 1 CPU time: 53.0s Max memory: 12582912 KiB Used memory: 11388608 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0 virsh # dommemstat 2 actual 3000000 rss 599036 4) Restart the SAME vm with 4GB of Current and Max (4194304) 2013-03-22 21:20:58.894+0000: 23182: debug : qemuMonitorSetBalloon:1690 : mon=0x7f3d643eb5a0 newmem=4194304 2013-03-22 21:20:58.894+0000: 23182: debug : virJSONValueToString:1133 : result={"execute":"balloon","arguments":{"value":4294967296},"id":"libvirt-6"} 2013-03-22 21:20:58.894+0000: 23182: debug : qemuMonitorJSONCommandWithFd:265 : Send command '{"execute":"balloon","arguments":{"value":4294967296},"id":"libvirt-6"}' for write with FD -1 2013-03-22 21:20:58.894+0000: 23182: debug : qemuMonitorSend:903 : QEMU_MONITOR_SEND_MSG: mon=0x7f3d643eb5a0 msg={"execute":"balloon","arguments":{"value":4294967296},"id":"libvirt-6"} 2013-03-22 21:20:58.894+0000: 23179: debug : qemuMonitorIOWrite:461 : QEMU_MONITOR_IO_WRITE: mon=0x7f3d643eb5a0 buf={"execute":"balloon","arguments":{"value":4294967296},"id":"libvirt-6"} virsh # dominfo 3 Id: 3 Name: centos_jt UUID: bc25a6c4-ba34-a593-47c7-6372999946d6 OS Type: hvm State: running CPU(s): 1 CPU time: 15.4s Max memory: 4194304 KiB Used memory: 4194304 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0 virsh # dommemstat 3 actual 4194304 rss 431384 5) reduce ram to 1GB (Works) virsh # setmem 3 --live --config --size 1048576 2013-03-22 21:26:08.783+0000: 23183: debug : qemuMonitorSetBalloon:1690 : mon=0x7f3d643eb5a0 newmem=1048576 2013-03-22 21:26:08.783+0000: 23183: debug : virJSONValueToString:1133 : result={"execute":"balloon","arguments":{"value":1073741824},"id":"libvirt-11"} 2013-03-22 21:26:08.783+0000: 23183: debug : qemuMonitorJSONCommandWithFd:265 : Send command '{"execute":"balloon","arguments":{"value":1073741824},"id":"libvirt-11"}' for write with FD -1 2013-03-22 21:26:08.783+0000: 23183: debug : qemuMonitorSend:903 : QEMU_MONITOR_SEND_MSG: mon=0x7f3d643eb5a0 msg={"execute":"balloon","arguments":{"value":1073741824},"id":"libvirt-11"} 2013-03-22 21:26:08.784+0000: 23179: debug : qemuMonitorIOWrite:461 : QEMU_MONITOR_IO_WRITE: mon=0x7f3d643eb5a0 buf={"execute":"balloon","arguments":{"value":1073741824},"id":"libvirt-11"} 2013-03-22 21:26:08.789+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d643eb5a0 buf={"timestamp": {"seconds": 1363987568, "microseconds": 789570}, "event": "BALLOON_CHANGE", "data": {"actual": 4293918720}} 2013-03-22 21:26:08.789+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363987568, "microseconds": 789570}, "event": "BALLOON_CHANGE", "data": {"actual": 4293918720}}] 2013-03-22 21:26:08.789+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363987568, "microseconds": 789570}, "event": "BALLOON_CHANGE", "data": {"actual": 4293918720}} 2013-03-22 21:26:08.789+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d643eb5a0 event={"timestamp": {"seconds": 1363987568, "microseconds": 789570}, "event": "BALLOON_CHANGE", "data": {"actual": 4293918720}} 2013-03-22 21:26:08.789+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x1686360 2013-03-22 21:26:08.789+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d643eb5a0 2013-03-22 21:26:08.789+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 4194304 to 4193280 kb 2013-03-22 21:26:09.789+0000: 23179: debug : qemuMonitorIOProcess:353 : QEMU_MONITOR_IO_PROCESS: mon=0x7f3d643eb5a0 buf={"timestamp": {"seconds": 1363987569, "microseconds": 408889}, "event": "BALLOON_CHANGE", "data": {"actual": 1073741824}} 2013-03-22 21:26:09.789+0000: 23179: debug : qemuMonitorJSONIOProcessLine:152 : Line [{"timestamp": {"seconds": 1363987569, "microseconds": 408889}, "event": "BALLOON_CHANGE", "data": {"actual": 1073741824}}] 2013-03-22 21:26:09.789+0000: 23179: debug : virJSONValueFromString:975 : string={"timestamp": {"seconds": 1363987569, "microseconds": 408889}, "event": "BALLOON_CHANGE", "data": {"actual": 1073741824}} 2013-03-22 21:26:09.789+0000: 23179: debug : qemuMonitorJSONIOProcessLine:167 : QEMU_MONITOR_RECV_EVENT: mon=0x7f3d643eb5a0 event={"timestamp": {"seconds": 1363987569, "microseconds": 408889}, "event": "BALLOON_CHANGE", "data": {"actual": 1073741824}} 2013-03-22 21:26:09.789+0000: 23179: debug : qemuMonitorJSONIOProcessEvent:138 : handle BALLOON_CHANGE handler=0x4b4de0 data=0x16826e0 2013-03-22 21:26:09.789+0000: 23179: debug : qemuMonitorEmitBalloonChange:1151 : mon=0x7f3d643eb5a0 2013-03-22 21:26:09.789+0000: 23179: debug : qemuProcessHandleBalloonChange:1248 : Updating balloon from 4193280 to 1048576 kb virsh # dominfo 3 Id: 3 Name: centos_jt UUID: bc25a6c4-ba34-a593-47c7-6372999946d6 OS Type: hvm State: running CPU(s): 1 CPU time: 28.6s Max memory: 4194304 KiB Used memory: 1048576 KiB Persistent: yes Autostart: disable Managed save: no Security model: none Security DOI: 0 virsh # dommemstat 3 actual 1048576 rss 411740