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

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Date:	Tue, 15 Jun 2010 10:12:44 +0300
From:	Avi Kivity <avi@...hat.com>
To:	balbir@...ux.vnet.ibm.com
CC:	Dave Hansen <dave@...ux.vnet.ibm.com>, kvm <kvm@...r.kernel.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache
 control

On 06/14/2010 08:16 PM, Balbir Singh wrote:
> * Dave Hansen<dave@...ux.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.

-- 
error compiling committee.c: too many arguments to function

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