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

[Nick Couchman]

> 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.

Ah, this I did not know, though I wondered if it were the case based on the fact that the original post that Andrew pointed me toward included patches for the blktap drivers.  So, is there any way to make this work using a physical device (like a logical volume) as the disk?

-Nick





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

[Keir Fraser]

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

> Hopefully someone from xen-devel can help us with this feature..