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Thread: KVM Memory Balloon does not work after boot

  1. #1
    Join Date
    Apr 2014

    KVM Memory Balloon does not work after boot


    I'm running Ubuntu 14.04 with KVM and Libvirt, and I'm attempting to get memory ballooning to work.

    Initially, I had trouble with the program I'm using to deploy vms (It's home grown, but essentially, it creates libvirt XML configs to deploy vms), and I was setting <currentMemory> to 1. As the VM was booting I could watch the currentMemory increasing and decreasing via Virt-Manager even though the VM would kernel panic. Once I got that issue solved I'm setting currentMemory to 1024MB and memory to 4096MB and the VM boots with 1024MB of RAM, but it never acquires more RAM as memory pressure is increased (in fact the kernel kills the process when it tries to use too much memory, stress also fails to allocate the appropriate memory).

    Note: I've intentionally deployed these vms without swap with the intent I would use memory ballooning in lieu of swap. Since I'm using Ceph on the backend for storage, "swap space" is really network storage which is less than ideal.

    What do I need to do from the guest side to get memory ballooning to work? the manpage for virtio_balloon is from freebsd and I'm not sure that it applies... according to this forum post it seems like I should just be able to set currentMemory and memory to different settings and set the memballoon model to be able to have memory ballooning work (my xml config doesn't define the address, it's autogenerated at runtime it seems)

    Here's the nitty gritty, I'm doing a "watch -n .5 free -m" while running these tests:

    stress command to test memory usage (interestingly the same command fails and I have to modify the multiplier .9 to .88/ the .9 multiplier fails intermittently) found here:

    root@trusty64:/lib/modules/3.13.0-24-generic# stress --vm-bytes $(awk '/MemFree/{printf "%d\n", $2 * .9 }' < /proc/meminfo)k --vm-keep -m 1 
    stress: info: [5477] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
    root@trusty64:/lib/modules/3.13.0-24-generic# stress --vm-bytes $(awk '/MemFree/{printf "%d\n", $2 * .9 }' < /proc/meminfo)k --vm-keep -m 1 
    stress: info: [5493] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
    stress: FAIL: [5494] (495) hogvm malloc failed: Cannot allocate memory
    stress: FAIL: [5493] (395) <-- worker 5494 returned error 1
    stress: WARN: [5493] (397) now reaping child worker processes
    stress: FAIL: [5493] (452) failed run completed in 0s
    Perl command to stress memory, second one is just to allow "watch" to keep up (e.g. it artificially slows down the loop)

    perl -E 'while (1) { $foo .= "X" x 8 }'
    perl -E 'while (1) { $foo .= "X" x 8; select undef, undef, undef, .0000000001 }'
    root@trusty64:~# perl -E 'while (1) { $foo .= "X" x 8 }'
    Out of memory!
    root@trusty64:~# perl -E 'while (1) { $foo .= "X" x 8; select undef, undef, undef, .0000000001 }'
    Out of memory!
    Here's my VM config and template:

    vm command line:

    I think the important bits are (interestingly, I don't see 1024 specified, which is the minimum memory):

    qemu-system-x86_64 -enable-kvm -m 4096 -realtime mlock=off -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8

    And here's the full line:
    qemu-system-x86_64 -enable-kvm -name ubuntu-14.04-balloon -S -machine pc-i440fx-1.4,accel=kvm,usb=off -m 4096 -realtime mlock=off -smp 2,sockets=2,cores=1,threads=1 
    -uuid 0cb8db1c-44f5-4093-b2d2-0fc957a38ed8 -no-user-config -nodefaults 
    -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/ubuntu-14.04-balloon.monitor,server,nowait 
    -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot menu=off,strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 
    -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -drive file=rbd:libvirt-pool/ubuntu-14.04-balloon-os:auth_supported=none:mon_host=\:6789\;\:6789\;\:6789,if=none,id=drive-virtio-disk0 
    -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -drive file=rbd:libvirt-pool/ubuntu-14.04-balloon-storage:auth_supported=none:mon_host=\:6789\;\:6789\;\:6789,if=none,id=drive-virtio-disk1 
    -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk1,id=virtio-disk1 -netdev tap,fd=31,id=hostnet0,vhost=on,vhostfd=32 
    -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:09:37:e7,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 
    -vnc -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 
    -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8
    Template (note: the second line is the evaluated variable):

    <domain type='kvm'>
      <memory unit='KiB'>[% guest.memory %]</memory>
      <memory unit='KiB'>4194304</memory>
      <currentMemory unit='KiB'>[% guest.current_memory %]</currentMemory>
      <currentMemory unit='KiB'>1048576</currentMemory>
      <vcpu placement='static'>[% guest.vcpu %]</vcpu>
      <vcpu placement='static'>2</vcpu>
        <min_guarantee unit='KiB'>[% guest.current_memory %]</min_guarantee>
        <min_guarantee unit='KiB'>1048576</min_guarantee>
        <memballoon model='virtio'>
    And here is the config of the dumped from libvirt:

    <domain type='kvm'>
      <memory unit='KiB'>4194304</memory>
      <currentMemory unit='KiB'>1048576</currentMemory>
        <min_guarantee unit='KiB'>1048576</min_guarantee>
      <vcpu placement='static'>2</vcpu>
        <memballoon model='virtio'>      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>

    And this is the /proc/meminfo of the guest:

    MemTotal:         902620 kB
    MemFree:          783208 kB
    Buffers:           17892 kB
    Cached:             8712 kB
    SwapCached:            0 kB
    Active:            37712 kB
    Inactive:          14492 kB
    Active(anon):      25716 kB
    Inactive(anon):      264 kB
    Active(file):      11996 kB
    Inactive(file):    14228 kB
    Unevictable:           0 kB
    Mlocked:               0 kB
    SwapTotal:             0 kB
    SwapFree:              0 kB
    Dirty:                24 kB
    Writeback:             0 kB
    AnonPages:         25608 kB
    Mapped:             3028 kB
    Shmem:               380 kB
    Slab:              29360 kB
    SReclaimable:      20096 kB
    SUnreclaim:         9264 kB
    KernelStack:         720 kB
    PageTables:         2960 kB
    NFS_Unstable:          0 kB
    Bounce:                0 kB
    WritebackTmp:          0 kB
    CommitLimit:      451308 kB
    Committed_AS:      72476 kB
    VmallocTotal:   34359738367 kB
    VmallocUsed:       14340 kB
    VmallocChunk:   34359715068 kB
    HardwareCorrupted:     0 kB
    AnonHugePages:      2048 kB
    HugePages_Total:       0
    HugePages_Free:        0
    HugePages_Rsvd:        0
    HugePages_Surp:        0
    Hugepagesize:       2048 kB
    DirectMap4k:       45048 kB
    DirectMap2M:     4149248 kB
    I appreciate any advice.

  2. #2
    Join Date
    Feb 2015

    Re: KVM Memory Balloon does not work after boot

    I'm having the same issue, though I have not so thoroughly investigated the issue. I did a similar stress test in python and have the same type of results: memory fills, swap fills, and then the script is killed. All the while, no "balooning" is seen. You may have already checked this, but I found this thread ( interesting. If you haven't already, ensure the guest has the appropriate modules or kernel. In my case, I used Ubuntu Server 14.04 and selected 'minimal virtual machine.' I'm hoping someone out there has the answer/solution to this issue...

  3. #3
    Join Date
    Mar 2010
    Lubuntu 14.04 Trusty Tahr

    Re: KVM Memory Balloon does not work after boot says:
    That's the problem with the current balloon device, it's entirely manual. Someone (or some tool) is supposed to be watching the pressure in the host and guest and then operate the balloon accordingly. This doesn't work well in practice (if doable at all).
    Seems you beyond the bleeding edge. That page has git references and instructions to enable it.
    qemu [...] -device virtio-balloon,automatic=true
    I didn't see any "automatic" in the posted settings above.
    Last edited by TheFu; February 5th, 2015 at 12:22 PM.

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