linux-kernel - Re: [patch 1/9] Guest page hinting: unused / free pages.

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Date:	Tue, 12 Sep 2006 20:07:44 -0400
From:	Hubertus Franke <frankeh@...son.ibm.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	akpm@...l.org, nickpiggin@...oo.com.au, rhim@...gateh.edu
Subject: Re: [patch 1/9] Guest page hinting: unused / free pages.

Rik van Riel wrote:
> Martin Schwidefsky wrote:
> 
>> From: Martin Schwidefsky <schwidefsky@...ibm.com>
>> From: Hubertus Franke <frankeh@...son.ibm.com>
>> From: Himanshu Raj <rhim@...gatech.edu>
>>
>> [patch 1/9] Guest page hinting: unused / free pages.
>>
>> A very simple but already quite effective improvement in the handling
>> of guest memory vs. host memory is to tell the host when pages are
>> free. 
> 
> 
> Would it be an idea to place this interface in-between the
> per-cpu free page lists and the buddy allocator, so we can
> move a batch of pages around at once and do the hinting in
> a batched fashion ?
> 
> That way the overhead will be acceptable not just on S390
> (where things are millicoded), but also on hypervisor based
> virtualization like Xen.
> 
> Easy enough to pass a vector of pages to the hypervisor.
> 

Rik, I thought that what we did.
Martin, I see the code actually does it when the page goes into the hot/cold
list. I can't remember conciously moving to that.
I thought we had a decent hit on the hot/cold, so that bulking makes sense.

Then the interface of bulking could be introduced and for s390 it could internally
be implemented as a sequence of ESSA instruction.
Do you remember the reason why we ended up putting it as part of hot/cold freeing?

-- Hubertus

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