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

[Hubertus Franke <frankeh@watson.ibm.com>]

Rik van Riel wrote:
> Martin Schwidefsky wrote:
> 
>> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
>> From: Hubertus Franke <frankeh@watson.ibm.com>
>> From: Himanshu Raj <rhim@cc.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