Re: [Xen-devel] A Problem with Cache in Xen

[Tim Deegan <tim@xxxxxxx>]

Hi, 
At 08:55 +0800 on 13 Jan (1326444953), hxkhust wrote:
> On a physical machine with xen virtualization platform installed ,VM
>  A,VM B are VM C's virtual disks are all image files,among which VM A
>  and VM B's virtual disks are QCOW2 format and VM C's disk is RAW
>  format. And VM B and VM C's virtual disk image files are based on VM
>  A's virtual disk image file.Now these three VMs are running on the
>  same physical machine with xen installed. 
> 
>  In the process of running VM B get a page data from VM A's virtual
>  disk image file. After that ,VM C also need to get the same page data
>  as VM B got just now.Under this situation, does VMM copy the page
>  data from VM B's memory to VM C's memory or get the page data from VM
>  A's virtual disk image file in the physical disk again?

Since VM C's disk is not QCOW, reads will always come directly from VM
C's image -- never from VM A's image (since the tools wouldn't know how
to do that) and never by copying from VM B.

Tim.

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