Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control

Avi Kivity
2010-06-15T07:12:50Z

On 06/14/2010 08:16 PM, Balbir Singh wrote:
> * Dave Hansen<dave@linux.vnet.ibm.com> [2010-06-14 10:09:31]:
>
>
>> On Mon, 2010-06-14 at 22:28 +0530, Balbir Singh wrote:
>>
>>> If you've got duplicate pages and you know
>>> that they are duplicated and can be retrieved at a lower cost, why
>>> wouldn't we go after them first?
>>>
>> I agree with this in theory. But, the guest lacks the information about
>> what is truly duplicated and what the costs are for itself and/or the
>> host to recreate it. "Unmapped page cache" may be the best proxy that
>> we have at the moment for "easy to recreate", but I think it's still too
>> poor a match to make these patches useful.
>>
>>
> That is why the policy (in the next set) will come from the host. As
> to whether the data is truly duplicated, my experiments show up to 60%
> of the page cache is duplicated.

Isn't that incredibly workload dependent?

We can't expect the host admin to know whether duplication will occur or
not.

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