Re: [Qemu-devel] [RFC] support memory reserved feature and optimize mlock guest memory propose

[Zhanghailiang]

> Il 05/03/2014 09:01, Zhanghailiang ha scritto:
> > Hi all：
> >
> > Currently, we use cgroup(memory) to support memory QoS on KVM
> > platform, and use "mlock" on qemu to support "memory reserved".
> >
> > The "mlock" seems to be not appropriate.
> >
> > Now qemu "mlock" memory in the main thread, which would lock iothread
> > (qemu_mutex_lock_iothread), if the memory size is large, that will
> > consume lots of time.
> >
> > It means whenever we want to set a new 'mlock', the VM would be
> > blocked for a while.
> 
> I'm not sure I understand how the mlock-ed memory is used.  Are you using a
> custom malloc, for example with g_mem_set_vtable?
> 
> Paolo

Hi Paolo：

Thanks for your reply.
As you know qemu has an option "-mlock", I think it has some problems.
If we set "-realtime mlock=on", then qemu will mlockall vm's memory, It is a 
very time consuming action, and it will block the libvirt api until it finished.
so I think it is better to do 'mlock' asynchronously, the flow chart can be 
described like below. Is it ok? 
Flow chart:
           main funciton           qmp command "set_ram_minguarantee"
                 |                           |
                 |                           |
        create "mlock" thread           change value of lock_ram_size
                 |                           |
                 |                           |
    |------>thread wait<-------------wake up "mlock" thread
    |            |
    |            |
    |            |
    |-------mlock(lock_ram_zie)


zhanghailiang