[Users] hot add ram to a vm

[Andrew Cathrow]

----- Original Message -----
> From: "Sander Grendelman" <sander at grendelman.com>
> To: "Michal Skrivanek" <michal.skrivanek at redhat.com>
> Cc: users at ovirt.org
> Sent: Friday, December 13, 2013 8:52:42 AM
> Subject: Re: [Users] hot add ram to a vm
> 
> On Fri, Dec 13, 2013 at 1:42 PM, Michal Skrivanek
> <michal.skrivanek at redhat.com> wrote:
> > Too bad QEMU doesn't support it. So it's still a long way.
> 
> qemu/libvirt "kind of" supports it (at least in F19).
> 
> In virt-manager you can define "current" and "maximum" memory
> allocation.
> 
> The VM only sees the current allocation and you can hot add memory up
> to the maximum allocation.


It isn't really hot-plug.
This allows you to statically set the physical ram but then use the balloon device to "borrow" some ram from the guest.
If max memory was 4gb and we set current memory to 2gb the VM would still see 4gb of physical memory but the balloon driver would be taking up 2gb of memory in the guest, this memory would be returned to the host for other VMs to use.


> 
> Example from the xml definition:
> 
>   <memory unit='KiB'>3145728</memory>
>   <currentMemory unit='KiB'>1048576</currentMemory>
> 
> After booting:
> 
> [root at grkvm201 ~]# uname -a
> Linux grkvm201.plusine.intern 2.6.32-358.23.2.el6.x86_64 #1 SMP Wed
> Oct 16 18:37:12 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
> [root at grkvm201 ~]# free -lm
>              total       used       free     shared    buffers
>                  cached
> Mem:           837        296        540          0          8
>         84
> Low:           837        296        540
> High:            0          0          0
> -/+ buffers/cache:        203        634
> Swap:          511          0        511
> [root at grkvm201 ~]#
> 
> memory increased to 2GB through virt-manager:
> 
> [root at grkvm201 ~]# free -lm
>              total       used       free     shared    buffers
>                  cached
> Mem:          1861        295       1565          0          8
>         84
> Low:          1861        295       1565
> High:            0          0          0
> -/+ buffers/cache:        202       1659
> Swap:          511          0        511
> [root at grkvm201 ~]# cat /proc/meminfo
> MemTotal:        1906176 kB
> MemFree:         1603456 kB
> Buffers:            9140 kB
> Cached:            86860 kB
> SwapCached:            0 kB
> Active:            92564 kB
> Inactive:          68064 kB
> Active(anon):      68692 kB
> Inactive(anon):       12 kB
> Active(file):      23872 kB
> Inactive(file):    68052 kB
> Unevictable:       21600 kB
> Mlocked:           11380 kB
> SwapTotal:        524280 kB
> SwapFree:         524280 kB
> Dirty:                12 kB
> Writeback:             0 kB
> AnonPages:         86232 kB
> Mapped:            20436 kB
> Shmem:               288 kB
> Slab:              75132 kB
> SReclaimable:      14576 kB
> SUnreclaim:        60556 kB
> KernelStack:        1464 kB
> PageTables:         4224 kB
> NFS_Unstable:          0 kB
> Bounce:                0 kB
> WritebackTmp:          0 kB
> CommitLimit:     1477368 kB
> Committed_AS:     547624 kB
> VmallocTotal:   34359738367 kB
> VmallocUsed:       20040 kB
> VmallocChunk:   34359688500 kB
> HardwareCorrupted:     0 kB
> AnonHugePages:     18432 kB
> HugePages_Total:       0
> HugePages_Free:        0
> HugePages_Rsvd:        0
> 
> Memory decreased to 1,5GB through virt-manager:
> [root at grkvm201 ~]# free -lm
>              total       used       free     shared    buffers
>                  cached
> Mem:          1349        295       1054          0          8
>         84
> Low:          1349        295       1054
> High:            0          0          0
> -/+ buffers/cache:        201       1147
> Swap:          511          0        511
> [root at grkvm201 ~]#
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