Re: [RFC PATCH v2 00/15][Sorted-buddy] mm: Memory Power Management

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 05/29/2013 01:38 AM, Phillip Susi wrote:
> 
> On 4/19/2013 3:12 AM, Srivatsa S. Bhat wrote:
>> But going further, as I had mentioned in my TODO list, we can be
>> smarter than this while doing compaction to evacuate memory regions
>> - we can choose to migrate only the active pages, and leave the
>> inactive pages alone. Because, the goal is to actually consolidate
>> the *references* and not necessarily the *allocations* themselves.
> 
> That would help with keeping references compact to allow use of the
> low power states, but it would also be nice to keep allocations
> compact, and completely power off a bank of ram with no allocations.
> 

That is a very good point, thanks! But one of the differences we have to
keep in mind is that powering off a bank requires intervention from the
OS (ie., OS should initiate the power-off, because we lose the contents
on power-off) whereas going to lower power states can be mostly done
automatically by the hardware (because it is content-preserving).

But powering-off unused banks of RAM (using techniques such as PASR -
Partial Array Self Refresh) can give us more power-savings than just
entering lower power states. So yes, keeping allocations consolidated
has that additional advantage. And the sorted-buddy design of the page
allocator helps us achieve that.

Thanks a lot for your inputs, Phillip!

Regards,
Srivatsa S. Bhat

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