[Bug 1315402] [NEW] No easy way to use hugetlbfs with QEMU

[Simon Déziel]

Public bug reported:

In previous releases (tested with Saucy), if one wanted to use hugetlbfs
for a VM, the needed procedure was:

1) Add "vm.nr_hugepages" to /etc/sysctl.d/60-hugepages.conf
2) start procps
3) Set KVM_HUGEPAGES=1 in /etc/default/qemu-kvm
4) restart qemu-kvm
5) Enable "<memoryBacking> <hugepages/></memoryBacking>" in the libvirt guest definition
6) Restart the guest

Now with Trusty, this doesn't work anymore as there is no (obvious?) way
to have the hugetlbfs mounted where QEMU expects it.


On Saucy, the upstart job for qemu-kvm contains this:

	# mount hugepages if available and requested
	if [ "$KVM_HUGEPAGES" -eq "1" ]; then
		if ! grep -q hugetlbfs /proc/filesystems; then
			logger -t qemu-kvm "Error: hugepages not available in the kernel!"
		elif grep -q /run/hugepages/kvm /proc/mounts; then
			logger -t qemu-kvm "/run/hugepages/kvm already mounted"
		elif ! grep -q kvm /etc/group; then
			logger -t qemu-kvm "Error: group kvm does not exist!"
		else
			kvmgid=`grep kvm /etc/group | cut -d: -f 3`
			mkdir -p /run/hugepages/kvm
			mount -t hugetlbfs hugetlbfs-kvm -o mode=775,gid=$kvmgid /run/hugepages/kvm
		fi
	fi

But it seems there is nothing similar in Trusty and manually mounting
the hugetlbfs doesn't help as qemu cannot find it there.


Host information:

$ lsb_release -rd
Description:	Ubuntu 14.04 LTS
Release:	14.04
$ apt-cache policy qemu-system-x86 libvirt-bin
qemu-system-x86:
  Installed: 2.0.0+dfsg-2ubuntu1
  Candidate: 2.0.0+dfsg-2ubuntu1
  Version table:
 *** 2.0.0+dfsg-2ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     2.0.0~rc1+dfsg-0ubuntu3.1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main amd64 Packages
     2.0.0~rc1+dfsg-0ubuntu3 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
libvirt-bin:
  Installed: 1.2.2-0ubuntu13.1
  Candidate: 1.2.2-0ubuntu13.1
  Version table:
 *** 1.2.2-0ubuntu13.1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1.2.2-0ubuntu13 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: qemu-system-common 2.0.0+dfsg-2ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity
Date: Fri May  2 10:05:18 2014
InstallationDate: Installed on 2014-01-26 (95 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140124)
SourcePackage: qemu
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: qemu (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug package-from-proposed trusty

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Title:
  No easy way to use hugetlbfs with QEMU

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