Re: [Qemu-devel] incorrect memory size inside vm

[Andrey Korolyov]

On Wed, Jun 17, 2015 at 4:35 PM, Vasiliy Tolstov <address@hidden> wrote:
> Hi. I have issue with incorrect memory side inside vm. I'm try utilize
> memory balloon (not memory hotplug, because i have guest without
> memory hotplug (may be)).
>
> When domain started with static memory all works fine, but then i'm
> specify in libvirt
> memory = 16384 , maxMemory = 16384 and currentMemory = 1024, guest in
> f/rpoc/meminfo says that have only 603608 Kb memory. Then i set memory
> via virsh setmem to 2Gb, guest see only 1652184 Kb memory.
>
> software versions
> libvirt: 1.2.10
> qemu: 2.3.0
> Guest OS: centos 6.
>
> qemu.log:
> LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
> HOME=/root USER=root LOGNAME=root QEMU_AUDIO_DRV=none /usr/bin/kvm
> -name 26543 -S -machine pc-i440fx-1.7,accel=kvm,usb=off -m 1024
> -realtime mlock=off -smp 1,maxcpus=4,sockets=4,cores=1,threads=1 -uuid
> 4521fb01-c2ca-4269-d2d6-0000035fd910 -no-user-config -nodefaults
> -chardev 
> socket,id=charmonitor,path=/var/lib/libvirt/qemu/26543.monitor,server,nowait
> -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc
> -no-shutdown -boot strict=on -device
> piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device
> virtio-scsi-pci,id=scsi0,num_queues=1,bus=pci.0,addr=0x4 -device
> virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 -drive
> file=/dev/vg4/26543,if=none,id=drive-scsi0-0-0-0,format=raw,cache=none,discard=unmap,aio=native,iops=5000
> -device 
> scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
> -drive if=none,id=drive-scsi0-0-1-0,readonly=on,format=raw -device
> scsi-cd,bus=scsi0.0,channel=0,scsi-id=1,lun=0,drive=drive-scsi0-0-1-0,id=scsi0-0-1-0
> -netdev tap,fd=30,id=hostnet0,vhost=on,vhostfd=52 -device
> virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:00:34:f7,bus=pci.0,addr=0x3,rombar=0
> -chardev pty,id=charserial0 -device
> isa-serial,chardev=charserial0,id=serial0 -chardev
> socket,id=charchannel0,path=/var/lib/libvirt/qemu/26543.agent,server,nowait
> -device 
> virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
> -device usb-mouse,id=input0 -device usb-kbd,id=input1 -vnc
> [::]:8,password -device VGA,id=video0,bus=pci.0,addr=0x2 -device
> virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 -object
> rng-random,id=rng0,filename=/dev/random -device
> virtio-rng-pci,rng=rng0,max-bytes=1024,period=2000,bus=pci.0,addr=0x7
> -msg timestamp=on
>
> --
> Vasiliy Tolstov,
> e-mail: address@hidden
>


The rest of visible memory is eaten by reserved kernel areas, for us
this was a main reason to switch to a hotplug a couple of years ago.
You would not be able to scale a VM by an order of magnitude with
regular balloon mechanism without mentioned impact, unfortunately.
Igor Mammedov posted hotplug-related patches for 2.6.32 a while ago,
though RHEL6 never adopted them by some reason.