Memory Sharing on HVM guests

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Memory Sharing on HVM guests

Lakshitha Harshan
I am a 4th year Computer Science undergraduate of University of Colombo School of Computing. We are required to do a research project on this year. So I have submitted a research proposal on optimizing the memory page sharing on xen. It has approved and now we are required implement it.

 I'm willing to implement it on Xen hypervisor 4.0.1, based on the previous work on memory page sharing for HVM guests in Xen 4.0.1. But I could not find sufficient documentation on these source codes. If someone can provide me the following details on memory page sharing on HVM, it would be a great help for me.
  1. Which source files are involved in implementation of memory page sharing
  2. When the mechanism is initiated to look for sharable pages and how
  3. How the page sharing mechanism works
  4. What happens if the owner of a shared page is quitting or trying to put the shared pages on disk

Thanking you.
Harshan

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Re: Memory Sharing on HVM guests

Tim Deegan-4
At 07:11 +0000 on 17 Feb (1297926672), Lakshitha Harshan wrote:
> I am a 4th year Computer Science undergraduate of University of
> Colombo School of Computing. We are required to do a research project
> on this year. So I have submitted a research proposal on optimizing
> the memory page sharing on xen. It has approved and now we are
> required implement it.

Excellent.  How do you plan to optimize it?

>  I'm willing to implement it on Xen hypervisor 4.0.1, based on the
> previous work on memory page sharing for HVM guests in Xen 4.0.1. But

I recommend working on the release candidate for 4.1.0 (4.1.0-rc5,
http://hg.uk.xensource.com/xen-unstable.hg/log/22929) where page sharing
is in much better shape.  MaoXiaoyun and Jui-Hao Chiang have been
working on it recently, and I hope will continue to do so after the
4.1.0 release.

> I could not find sufficient documentation on these source codes. If
> someone can provide me the following details on memory page sharing on
> HVM, it would be a great help for me.

You should start by searching the archives of xen-devel for the recent
threads about it, and using your favourite IDE to search the source code
for "memory sharing".

Cheers,

Tim.

>  1.  Which source files are involved in implementation of memory page sharing
>  2.  When the mechanism is initiated to look for sharable pages and how
>  3.  How the page sharing mechanism works
>  4.  What happens if the owner of a shared page is quitting or trying to put the shared pages on disk
>
> Thanking you.
> Harshan

> _______________________________________________
> Xen-devel mailing list
> [hidden email]
> http://lists.xensource.com/xen-devel


--
Tim Deegan <[hidden email]>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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Re: Memory Sharing on HVM guests

Jui-Hao Chiang-2
Hi, Harshan:

>
> I recommend working on the release candidate for 4.1.0 (4.1.0-rc5,
> http://hg.uk.xensource.com/xen-unstable.hg/log/22929) where page sharing
> is in much better shape.  MaoXiaoyun and Jui-Hao Chiang have been
> working on it recently, and I hope will continue to do so after the
> 4.1.0 release.
>

You can first go through the mailing list by searching the email
address of me and Xiaoyun.

As Tim said, the current mem_sharing code has race condition on p2m
type with p2m code. From Xiaoyun's testing result, the shared memory
pages can be grabbed/invalidated by others especially during guest
reboot. To solve the problem, we are digging into the p2m code (Tim
would probably have more time on this after the 4.1 release)

I have some scribble on my google document
https://docs.google.com/document/pub?id=16cK1JtXhhyNkGHtV_0XTkFnM2nkVxSP144EjozioC6w#h.y4a96-augwr7

If you like, send email and we can also discuss the details about what
we have done so far.

Bests,
Jui-Hao

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Re: Memory Sharing on HVM guests

Tim Deegan-4
In reply to this post by Tim Deegan-4
Hi,

Please don't take the mailing list out of the Cc: headers when replying
to email.

At 16:38 +0000 on 18 Feb (1298047104), Lakshitha Harshan wrote:
> I'm trying to optimize it by trying to reduce the number of page
> faults occurs as a result of sharing similar pages which have short
> life time.I'm still working on it. But the problem is understanding
> existing code. Also i'm having difficulties on installing Xen. I
> installed Xen 4.0.1 on Debian Lenny, but when i'm trying to create VMs
> it says "Hotplug scripts not working".

Have a look at http://wiki.xensource.com/xenwiki/XenCommonProblems

> So what is the best OS you suggest me to install xen 4.1.0?

It depends mostly on what distro you're most familiar with.  
I use debian 'squeeze' and it works OK.

Cheers,

Tim.

--
Tim Deegan <[hidden email]>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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Re: Memory Sharing on HVM guests

waitxie
This post has NOT been accepted by the mailing list yet.
In reply to this post by Jui-Hao Chiang-2
Hi, Jui-Hao,

I want to enable memory sharing in xen. I am a newbie in Xen. I searched in internet. There is few information about memory sharing. Your google document can not be access any more.

https://docs.google.com/document/pub?id=16cK1JtXhhyNkGHtV_0XTkFnM2nkVxSP144EjozioC6w#h.y4a96-augwr7

Can you give me some instruction about enabling memory sharing in xen?
Thanks.