Re: [Xen-devel] Copy-on write sharing

[Tim Deegan <tim@xxxxxxx>]

Hi,

At 01:39 -0700 on 31 May (1338428371), zhangzhi wrote:
> xen 4.0 release has said that it had a special feature of copy-on write
> sharing of identical memory pages between VMs (HVM only). 
> I just wanna know the source code that illustrate this feature. 

The code inside the hypervisor lives in xen/arch/x86/mm/, mostly in the
file mem_sharing.c.

The user-space interface is in libxc, in tools/libxc/xc_memshr.c

An example program that uses it is tools/tests/mem-sharing/memshrtool.c.

This feature is not built in to the higher-level tools (libxl &c) at the
moment; originally there were extensions to blktap that could
automatically share pages that were read from disk if the VMs' disks
came from the same source image, but I think that's all bitrotted.  If
anyone wanted to try to get that working again, I'm sure it would be
welcome!

Cheers,

Tim.

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