about page cache architecture of the dom0 and domUs in xen platform

about page cache architecture of the dom0 and domUs in xen platform

[hxkhust]

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Hi,
I encounter a problem that has puzzled me for a long time.On a Xen virtualization platform, some VMs ,whose virtual disks are image files ,are running in DomUs.Under this situation ,does the Dom0 cache the pages from the VMs?Does the filesystem in Dom0 see the VMs as general processes?
 
HXK

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Re: about page cache architecture of the dom0 and domUs in xen platform

[Pasi Kärkkäinen]

On Wed, Feb 01, 2012 at 11:50:06AM +0800, hxkhust wrote:
>    Hi,
>    I encounter a problem that has puzzled me for a long time.On a Xen
>    virtualization platform, some VMs ,whose virtual disks are image files
>    ,are running in DomUs.Under this situation ,does the Dom0 cache the pages
>    from the VMs?Does the filesystem in Dom0 see the VMs as general processes?
> 

It depends which disk backend driver you're using for the domU disks..
(file: or tap:aio:)

-- Pasi

Re: about page cache architecture of the dom0 and domUs in xen platform

[hxkhust]

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Hi,Pasi Kärkkäinen,
 
In most cases, I use "file:/..." or "tap:qcow2:..."  for my VMs.When I use "tap:aio:.." in the configuration,somgthing wrong will happen.At the first time I speculate that the blktap/blktap2 module is not installed successfully.Thus some time ago I try to figure out the problem.However I failed in the end.Could you tell me the difference between "file:" and "tap:aio" from the page cache architecture side?
The answer to this question is of importance for me.I need your help.Thank you. 

HXK



At 2012-02-01 15:51:00,"Pasi Kärkkäinen" <pasik@iki.fi> wrote:
>On Wed, Feb 01, 2012 at 11:50:06AM +0800, hxkhust wrote:
>>    Hi,
>>    I encounter a problem that has puzzled me for a long time.On a Xen
>>    virtualization platform, some VMs ,whose virtual disks are image files
>>    ,are running in DomUs.Under this situation ,does the Dom0 cache the pages
>>    from the VMs?Does the filesystem in Dom0 see the VMs as general processes?
>> 
>
>It depends which disk backend driver you're using for the domU disks..
>(file: or tap:aio:)
>
>-- Pasi
>

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Re: about page cache architecture of the dom0 and domUs in xen platform

[hxkhust]

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Hi,Pasi Kärkkäinen,

At 2012-02-01 15:51:00,"Pasi Kärkkäinen" <pasik@iki.fi> wrote:
>On Wed, Feb 01, 2012 at 11:50:06AM +0800, hxkhust wrote:
>>    Hi,
>>    I encounter a problem that has puzzled me for a long time.On a Xen
>>    virtualization platform, some VMs ,whose virtual disks are image files
>>    ,are running in DomUs.Under this situation ,does the Dom0 cache the pages
>>    from the VMs?Does the filesystem in Dom0 see the VMs as general processes?
>> 
>
>It depends which disk backend driver you're using for the domU disks..
>(file: or tap:aio:)
>
>-- Pasi
>
 
In the last email I top-post and Tim remind me of that ,so I send the same content to you again. 

In most cases, I use "file:/..." or "tap:qcow2:..."  for my VMs.When I use "tap:aio:.." in the configuration,somgthing wrong will happen.At the first time I speculate that the blktap/blktap2 module is not installed successfully.Thus some time ago I try to figure out the problem.However I failed in the end.Could you tell me the difference between "file:" and "tap:aio" from the page cache architecture side?
The answer to this question is of importance for me.I need your help.Thank you. 

HXK



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