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Hi again,

I debugged the kernel codes and found out the root cause.

The sharing is not done for some pages causing error -E2BIG which is due to reference count being more than one. This prevents hypervor to nominate the page. As much as I know about this issue, the page that I want to nominate and I receive this error from make_page_sharable function in mem_sharing.c is pointed by more than one pages. So, is there any idea to resolve this issue? I though that I can put the page number in a buffer and share it again after t milliseconds but still the nomination return -E2BIG error. Am I missing something?

I would be grateful if you could help.

On Sat, Jul 28, 2018 at 11:13 AM sepanta s <sapanta992@xxxxxxxxx> wrote:

Thanks.
I would be thankful if he can help me ...

On Mon, Jul 23, 2018 at 11:52 AM Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> wrote:
On 07/23/2018 05:37 AM, sepanta s wrote:
> I have written a program that can share memory pages of two VMs every x
> milliseconds. To do so, I modified xen and added an unshare event to be
> able to capture it. However, for some pages, when I receive the unshare
> event that contains the information about the pages which was about to
> be written on and put it on a buffer for sharing them again after x
> milliseconds, I cannot nominate them again and an error occurs. So, the
> sharing mechanism I have built can partially share pages. I guess the
> problem might be because of internal structure of sharing mechanism in
> the Xen but can't figure out the problem.
> Do you have any idea what can cause this problem? Or what should I
> check to get closer to any solution?

I've never used this feature, but Tamas might have some insight into
this (added to Cc).

Re: [Xen-devel] An issue in sharing the pages again in xen-memshare