Re: [Xen-devel] Re: Xen 4 - Page Sharing HowTo?

Re: [Xen-devel] Re: Xen 4 - Page Sharing HowTo?

[Nick Couchman]

> 
> Should be unconditionally printed during Xen boot. Not when memory sharing
> is first used.

Yep, I see it!  What's the best way to tell how much memory or how many pages are being shared?  Will Xen's memory status (e.g. with xentop or xm list) show lower memory usage per machine?  Or is there somewhere else I need to dig to find how much memory is shared?

> 
>>> Also the 4.0 release announcement mentioned page to disk, but again I
>>> can find no reference to that... has anybody tested these new
>>> features?
> 
> I think you run the xenpaging daemon manually on each domain you want to
> have paged to disc. The daemon is probably under /usr/sbin/xenpaging. It
> takes two arguments: domain-id and memory allocated to the domain, in 4kB
> pages (e.g., memory in MB, multiplied by 256).
> 
>  -- Keir
> 

I think the RPMs I have are built without this - I cannot seem to locate it.  I'll have to see if I can compile it myself.

Thanks!

-Nick



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Re: Re: [Xen-users] Xen 4 - Page Sharing HowTo?

[Keir Fraser]

On 09/04/2010 17:28, "Nick Couchman" <Nick.Couchman@seakr.com> wrote:

>> Should be unconditionally printed during Xen boot. Not when memory sharing
>> is first used.
> 
> Yep, I see it!  What's the best way to tell how much memory or how many pages
> are being shared?  Will Xen's memory status (e.g. with xentop or xm list) show
> lower memory usage per machine?  Or is there somewhere else I need to dig to
> find how much memory is shared?

Sharing opportunities should result in memory being freed back to Xen. So
'xm info', or whatever else you use for monitoring Xen's free memory, should
work.

 -- Keir

Re: Re: [Xen-users] Xen 4 - Page Sharing HowTo?

[Nick Couchman]

> 
> Sharing opportunities should result in memory being freed back to Xen. So
> 'xm info', or whatever else you use for monitoring Xen's free memory, should
> work.
> 
>  -- Keir

Hmmm...two XP HVM domUs running, and a total of 7 M freed to Xen.  Kind of hard to tell if memory sharing is working, or if this is normal rounding behavior...

-Nick



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Re: [Xen-devel] Re: Xen 4 - Page Sharing HowTo?

[Keir Fraser]

On 09/04/2010 21:45, "Nick Couchman" <Nick.Couchman@seakr.com> wrote:

>> Sharing opportunities should result in memory being freed back to Xen. So
>> 'xm info', or whatever else you use for monitoring Xen's free memory, should
>> work.
>> 
>>  -- Keir
> 
> Hmmm...two XP HVM domUs running, and a total of 7 M freed to Xen.  Kind of
> hard to tell if memory sharing is working, or if this is normal rounding
> behavior...

The two images have to be using a common disc image (or a delta of a common
disc image) exported by a memshr-aware block-device backend: blktap1 or
blktap2. In fact, would have to be the former, since blktap2 has memshr
support disabled as it was crashing. The sharing opportunities aren't
discovered by page scanning, as in some other schemes.

 -- Keir

Re: Re: [Xen-users] Xen 4 - Page Sharing HowTo?

[Keir Fraser]

On 09/04/2010 15:59, "Andrew Lyon" <andrew.lyon@gmail.com> wrote:

> ERROR Internal error: Error flushing ioemu cache
> ERROR Internal error: Error mapping page
> 
> Perhaps there are hardware requirements for page to disk?
> 
> Any idea what I need to do to have memory sharing support compiled
> into blktap2? The combination of memory sharing + blktap2 results in
> this error when I try to start a vm:
> 
> using config file "./jos-ts3.cfg".
> Error: Failed to create device.
>     stdout:
>     stderr: MEMSHR support not compiled in.
> Check that target "/mnt/tb1_store/Xen_VMs/WinXP/WinXP.hda" exists and
> that blktap2 driver installed in dom0.

Tbh I think these features are barely even tech preview in the 4.0.0
release. They got little testing and the devs who implemented them are also
off doing other things at least part time. I hope they will get some more
love before 4.0.1.

 -- Keir

Re: Re: [Xen-users] Xen 4 - Page Sharing HowTo?

[Andrew Lyon]

On Fri, Apr 9, 2010 at 3:36 PM, Keir Fraser <keir.fraser@eu.citrix.com> wrote:
> On 09/04/2010 15:09, "Pasi Kärkkäinen" <pasik@iki.fi> wrote:
>
>>>> void mem_sharing_init(void)
>>>> {
>>>>    printk("Initing memory sharing.\n");
>>>>
>>>>
>>>> But I've not seen that at all on my 4.x system.
>
> Should be unconditionally printed during Xen boot. Not when memory sharing
> is first used.
>
>>> Also the 4.0 release announcement mentioned page to disk, but again I
>>> can find no reference to that... has anybody tested these new
>>> features?
>
> I think you run the xenpaging daemon manually on each domain you want to
> have paged to disc. The daemon is probably under /usr/sbin/xenpaging. It
> takes two arguments: domain-id and memory allocated to the domain, in 4kB
> pages (e.g., memory in MB, multiplied by 256).
>
>  -- Keir

Hmm, I tried that but as soon as I run xenpaging it outputs lots of errors:


ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error flushing ioemu cache
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page
ERROR Internal error: Error mapping page

Perhaps there are hardware requirements for page to disk?

Any idea what I need to do to have memory sharing support compiled
into blktap2? The combination of memory sharing + blktap2 results in
this error when I try to start a vm:

using config file "./jos-ts3.cfg".
Error: Failed to create device.
    stdout:
    stderr: MEMSHR support not compiled in.
Check that target "/mnt/tb1_store/Xen_VMs/WinXP/WinXP.hda" exists and
that blktap2 driver installed in dom0.

Andy