Question about using "qemu-kvm" to create vm including "-mem-path"

Question about using "qemu-kvm" to create vm including "-mem-path"

[Min Du]

Hi everyone,

I was wondering if anyone could answer my confusion here. I am using qemu-kvm 0.12.1 installed with centos-6.5. I would like to use large pages to back my guest vm, so I did it as this: http://www.linux-kvm.org/page/UsingLargePages, and added "-mem-path /hugetlbfs" in the command to create VM. When things went well, after creating vm, I type "tail /proc/meminfo", it would show like this, which means "HugePages" was used:
[root@mind domain]# tail /proc/meminfo 
VmallocChunk:   34359481380 kB
HardwareCorrupted:     0 kB
AnonHugePages:   1368064 kB
HugePages_Total:     512
HugePages_Free:      384
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:        6144 kB
DirectMap2M:    12552192 kB

However if I add "root=/dev/vda1" in the command to create vm, which looks like "-append root=/dev/vda1 console=ttyS0" in command line, then "-mem-path /hugetlbfs" doesn't work:
[root@mind domain]# tail /proc/meminfo 
VmallocChunk:   34359481380 kB
HardwareCorrupted:     0 kB
AnonHugePages:   1390592 kB
HugePages_Total:     512
HugePages_Free:      512
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:        6144 kB
DirectMap2M:    12552192 kB

Does anyone know how does "root=/dev/vda1" conflict with hugepages and how do I use both of them to create a VM? I am actually using an xml file to create VM, and those commands I mentioned above are shown in "ps aux | grep qemu".

Thanks,
Min

Re: Question about using "qemu-kvm" to create vm including "-mem-path"

[Paolo Bonzini]

Il 10/09/2014 01:54, Min Du ha scritto:
> However if I add "root=/dev/vda1" in the command to create vm, which
> looks like "-append root=/dev/vda1 console=ttyS0" in command line, then
> "-mem-path /hugetlbfs" doesn't work:
> [root@mind domain]# tail /proc/meminfo 
> VmallocChunk:   34359481380 kB
> HardwareCorrupted:     0 kB
> AnonHugePages:   1390592 kB
> HugePages_Total:     512
> HugePages_Free:      512
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:       2048 kB
> DirectMap4k:        6144 kB
> DirectMap2M:    12552192 kB
> 
> Does anyone know how does "root=/dev/vda1" conflict with hugepages
> and how do I use both of them to create a VM? I am actually using an xml
> file to create VM, and those commands I mentioned above are shown in "ps
> aux | grep qemu".

There should be no conflict.  Try reproducing with a more recent version
of QEMU.

Paolo