[OmniOS-discuss] qemu-system-x86_64 can not locked enough memory

[Joshua M. Clulow]

On 1 December 2015 at 09:11, Dan McDonald <danmcd at omniti.com> wrote:
>> On Dec 1, 2015, at 12:03 PM, Fucai.Liang <fcliang at baolict.com> wrote:
>> then I start the third vm (4G memory), it got the following error :
>> qemu-system-x86_64 -enable-kvm -vnc 0.0.0.0:2 -cpu host -smp 2 -m 4096 -no-hpet
>>
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying...
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying...
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying...
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying...
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying...
>> qemu_mlock: have only locked 1940582400 of 4294967296 bytes; still trying…
>>
>> I got 15G free memory in the system, why qemu-system-x86_64 can not locked enough memory ？
> What does "vmstat 1 5" say prior to your launch of the third VM?

I suspect it will show you have free memory available, but that what
is really happening is getting here:

  https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/vm/seg_vn.c#L7989-L8002

This is likely failing in page_pp_lock() because "availrmem" has
fallen below "pages_pp_maximum":

  https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/vm/vm_page.c#L3817-L3818

We set this value here, though it can be overridden in "/etc/system":

  https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/common/vm/vm_page.c#L423-L436

You can look at the current values with mdb:

  mdb -ke 'availrmem/D ; pages_pp_maximum/D'

Increasing this value doesn't seem to be without risk: I believe that
it can lead to memory exhaustion deadlocks, amongst other things.  I
don't know if it's expected to be tuneable without a reboot.


Cheers.

-- 
Joshua M. Clulow
UNIX Admin/Developer
http://blog.sysmgr.org