[libvirt] Problem with setting up KVM guests to use HugePages

[Clarylin L]

On Thu, Jun 11, 2015 at 12:00 AM, Michal Privoznik <mprivozn at redhat.com>
wrote:

> [please keep the list CC'ed]
>
> On 10.06.2015 20:09, Clarylin L wrote:
> > Hi Michal,
> >
> > Thanks a lot.
> >
> > If 100 hugepages are pre-allocated, the guest can start without
> decreasing
> > number of hugepages. Since the guest requires 128 hugepages, it's kind of
> > expected that the guest would not take memory from hugepages.
> >
> > Before guest start,
> >
> > [root at local ~]# cat /proc/meminfo | grep uge
> >
> > AnonH*uge*Pages:         0 kB
> >
> > H*uge*Pages_Total:     100
> >
> > H*uge*Pages_Free:      100
> >
> > H*uge*Pages_Rsvd:        0
> >
> > H*uge*Pages_Surp:        0
> > H*uge*pagesize:    1048576 kB
> >
> > After:
> >
> > [root at local ~]# cat /proc/meminfo | grep uge
> >
> > AnonH*uge*Pages:  134254592 kB
> >
> > H*uge*Pages_Total:     100
> >
> > H*uge*Pages_Free:      100
> >
> > H*uge*Pages_Rsvd:        0
> >
> > H*uge*Pages_Surp:        0
> > H*uge*pagesize:    1048576 kB
> >
> > There is no -mem-prealloc and -mem-path options in qemu command
>
> And there can't be. From the command line below, you are defining 2 NUMA
> nodes for your guest. In order to instruct qemu to back their memory by
> huge pages you need it to support memory-backend-file object which was
> introduced in qemu-2.1.0.
> The other option you have is to not use guest NUMA nodes, in which case
> global -mem-path can be used.
>

Michal, you were correct. My current version is qemu-1.5.3. After I updated
it to 2.1.2, I was able to use <page> element under <hugepages> and the
problem was solved. Seemed <page> element was required -- without using it,
start guest would report an error.

>
> >
> > [root at local ~]# ps -ef | grep qemu
> >
> > *qemu*      3403     1 99 17:42 ?        00:36:42 /usr/libexec/*qemu*-kvm
> > -name qvpc-di-03-sf -S -machine pc-i440fx-rhel7.0.0,accel=kvm,usb=off
> -cpu
> > host -m 131072 -realtime mlock=off -smp 32,sockets=2,cores=16,threads=1
> > -numa node,nodeid=0,cpus=0-15,mem=65536 -numa
> > node,nodeid=1,cpus=16-31,mem=65536 -uuid
> > e1b72349-4a0b-4b91-aedc-fd34e92251e4 -smbios type=1,serial=SCALE-SLOT-03
> > -no-user-config -nodefaults -chardev
> >
> socket,id=charmonitor,path=/var/lib/libvirt/*qemu*/qvpc-di-03-sf.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
> -drive
> >
> file=/var/lib/libvirt/images/asr5700/qvpc-di-03-sf-hda.img,if=none,id=drive-ide0-0-0,format=qcow2
> > -device
> > ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=2
> -drive
> > if=none,id=drive-ide0-1-0,readonly=on,format=raw -device
> > ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0,bootindex=1
> > -chardev pty,id=charserial0 -device
> > isa-serial,chardev=charserial0,id=serial0 -chardev pty,id=charserial1
> > -device isa-serial,chardev=charserial1,id=serial1 -vnc 127.0.0.1:0 -vga
> > cirrus -device i6300esb,id=watchdog0,bus=pci.0,addr=0x3 -watchdog-action
> > reset -device vfio-pci,host=08:00.0,id=hostdev0,bus=pci.0,addr=0x5
> -device
> > vfio-pci,host=09:00.0,id=hostdev1,bus=pci.0,addr=0x6 -device
> > vfio-pci,host=0a:00.0,id=hostdev2,bus=pci.0,addr=0x7 -device
> > virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -msg timestamp=on
> >
> >
> > If 140 hugepages are preallocated, the guest cannot start and it
> complained
> > not enough memory.
> >
> >
> > The libvirt version is shown as follows:
> >
> > virsh # version
> >
> > Compiled against library: libvirt 1.2.8
> >
> > Using library: libvirt 1.2.8
> >
> > Using API: QEMU 1.2.8
> >
> > Running hypervisor: QEMU 1.5.3
> >
> >
>
>
>
> > Also in guest configuration contains numa session. The hugepages are
> > uniformly distributed to two nodes. In this case, do I need to make
> > additional configurations to enable usage of hugepages?
> >
> >   <numatune>
> >
> >     <memory mode='strict' nodeset='0-1'/>
> >
> >   </numatune>
> >
>
> This says that all the memory for you guests should be pinned onto host
> nodes 0-1. If you want to be more specific, you can explicitly wire
> guest NUMA nodes onto host NUMA nodes in 1:N relationship (where N can
> be even 1, in which case you will get 1:1), e.g.:
>
> <memnode cellid='0' mode='preferred' nodeset='0'/>
>
> Michal
>
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