Re: [Qemu-devel] Persistent Main Memory in QEmu

[Dr. David Alan Gilbert]

* Li, Tianyou (address@hidden) wrote:
> Hi Dave,
> 
> Thanks for your response. Below are my explanations:
> 
> > Can you explain what you mean by 'persistent' - where do you intend to 
> > store the guests memory?
> 
> There could be a file or memory region that can survive across guest 
> shutdown/reboot. Seems Artyom has pointed out the right direction and I have 
> verified by looking into the code throughout the call stack from 
> pc_memory_init to qemu_ram_alloc_from_file. I plan to write something like 
> kernel module to verify the persistency characteristics from guest point of 
> view.

Maybe it's worth checking the stuff in docs/memory-hotplug.txt - that shows how 
to create a
memory region backed by a file (in that case using a hugepagefs - but I think 
it's general).
Note, I don't think there's a way to use that at the moment for main PC memory.

> 
> > Also, remember that you'll need to save/load the device state as well as 
> > the rest of RAM.  
> 
> Device state handling could be done from two different aspects: 1. From host 
> perspective or, 2. From guest perspective. From host, qemu will always know 
> the state of guest devices so that we can use qemu command to checkpoint 
> states, as you point out (very appreciated that, I do not know the command 
> xen-save-devices-state before). From guest, it can be something like suspend 
> to RAM or S3 for PC to checkpoint the current state of PC and restore them 
> when wakeup. Currently I will prefer the #2. 
> 
> In summary, I'd like to have the functionality in qemu that can save & 
> restore PC main memory at shutdown/power-on phase. Thanks.

Dave

> 
> Regards,
> Tianyou
> 
> 
> -----Original Message-----
> From: Dr. David Alan Gilbert [mailto:address@hidden 
> Sent: Wednesday, April 20, 2016 4:36 PM
> To: Li, Tianyou <address@hidden>
> Cc: address@hidden
> Subject: Re: [Qemu-devel] Persistent Main Memory in QEmu
> 
> * Li, Tianyou (address@hidden) wrote:
> > Hi,
> > 
> > Currently we are trying to implement below functionalities in QEmu: main 
> > memory in guest can be logically viewed as persistent and its content can 
> > be survived through reboot or shutdown/powerup.
> > 
> > I have looked into the QEmu memory management code include memory.c, exec.c 
> > and other related source, unfortunately I do not have the chance to get 
> > clue of how to make QEmu main memory persistent. I found that 
> > pmemsave<http://doc.opensuse.org/documentation/html/openSUSE_114/opensuse-kvm/cha.qemu.monitor.html#id547777>
> >  could dump physical memory of guest, but I could not find how to restore 
> > the dump file before VM startup to execution.
> 
> Can you explain what you mean by 'persistent' - where do you intend to store 
> the guests memory?
> Also, remember that you'll need to save/load the device state as well as the 
> rest of RAM.  If you've got a way to preserve RAM then maybe hte 
> xen-save-devices-state qemu command could be used to store the rest of 
> devices.
> 
> Dave
> 
> > 
> > Could anyone provide some hints to me? Thanks in advance!
> > 
> > Regards,
> > Tianyou
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK