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xen-devel
Re: [Xen-devel] Xen Memory De-duplication
On Sun, Oct 10, 2010 at 10:54:58AM +0530, Aditya Gadre wrote:
> This kind of implementation will require the disk blocks from different
> DomUs to be mapped to same physical disk block.
> For example,
> 1) Shared read only filesystem
> 2) Union based filesystem
> 3) Virtual machine images deployed on a host filesystem which has
> deduplication enabled
>
I guess Xen blktap qcow* images should do? And maybe blktap2 VHD?
-- Pasi
> What kind of arrangement of filesystem is used in production environments
> for DomUs which host large number of VMs as in cloud enviorment?
>
> On Sun, Oct 10, 2010 at 5:10 AM, Dan Magenheimer
> <[1]dan.magenheimer@xxxxxxxxxx> wrote:
>
> I*m not an expert on it but I believe this sounds very similar to the
> page sharing implementation that already exists in Xen 4.0. The
> implementation in Xen only works on HVM guests and only on machines that
> have EPT though. The patches (which were accepted into Xen) were posted
> here:
>
>
>
>
> [2]http://lists.xensource.com/archives/html/xen-devel/2009-12/msg00797.html
>
>
>
> From: Aditya Gadre [mailto:[3]adivb2003@xxxxxxxxx]
> Sent: Saturday, October 09, 2010 11:56 AM
> To: [4]Xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Xen Memory De-duplication
>
>
>
> Aim is to implement Xen Memory Deduplication with minimum overhead.
>
> Our approach to de-duplication is as follows
>
> In most cases, Domain-U uses a small set of well-known operating systems
> such as Linux, FreeBSD and Microsoft Windows. In such environment many
> domains share read-only filesystems that contain operating system and
> frequently usedprogram files and libraries.Each domain has their own
> writable filesystems for storing data and temporary files. In this
> configuration, multiple pages scattered in different domains mostly
> happen to contain same disk block. So, in our approach to perform
> deduplication we intend to add a data structure in dom 0 which store
> disk block number and the machine frame number(MFN) when a read request
> for the read only code(and data) is made. Now when another domain U
> places the request for the block of code and Dom 0 recieves a request
> for I/O (DMA), it will first check into the data structure for the entry
> for the block. If it finds the block it will return the MFN of the
> already read page and map it to the requesting domain's PFN resulting in
> zero I/O processing time of blocks which are already read. This in turn
> results in de-duplication of the read only pages accessed by multiple
> domains without any overhead of hashing the page.
>
> Test case scenario:
>
> Consider a Dom0 linux kernel using a filesystem with deduplication
> enabled. Then we install a DomU kernel with the virtual disk as a image
> file on the disk(.img). Then we make multiple copies of the image to
> deploy multiple DomUs running same kernel. Now, as deduplication is
> enabled in the file system initially all the blocks of the domains will
> be pointing to the same disk blocks. Now when the kernel's are booted,
> they all will consume memory only once for the programs(code segment)
> loaded in the memory. Now as these OSs start to write to their own
> virtual filesystems the blocks of the image will be COW'ed by the
> filesystem resulting in different block number.
> Is such a approach implemented? We intend to implement this as a
> project. What are the suspected challanges?
>
> Regards,
> Aditya Gadre
>
> References
>
> Visible links
> 1. mailto:dan.magenheimer@xxxxxxxxxx
> 2. http://lists.xensource.com/archives/html/xen-devel/2009-12/msg00797.html
> 3. mailto:adivb2003@xxxxxxxxx
> 4. mailto:Xen-devel@xxxxxxxxxxxxxxxxxxx
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