On Sat, Jun 11, 2011 at 10:26:54AM -0700, Arjan van de Ven wrote:

On Sat, 11 Jun 2011 10:06:10 -0700
"Paul E. McKenney" [off-list ref] wrote:

quoted

On Fri, Jun 10, 2011 at 08:02:33PM -0700, Arjan van de Ven wrote:

quoted

On Fri, 10 Jun 2011 12:37:13 -0700
"Paul E. McKenney" [off-list ref] wrote:

quoted

On Fri, Jun 10, 2011 at 08:23:29PM +0100, Matthew Garrett wrote:

quoted

On Fri, Jun 10, 2011 at 11:47:38AM -0700, Paul E. McKenney
wrote:

quoted

And if I understand you correctly, then the patches that
Ankita posted should help your self-refresh case, along with
the originally intended the power-down case and
special-purpose use of memory case.

Yeah, I'd hope so once we actually have capable hardware.

Cool!!!

So Ankita's patchset might be useful to you at some point, then.

Does it look like a reasonable implementation?

as someone who is working on hardware that is PASR capable right
now, I have to admit that our plan was to just hook into the buddy
allocator, and use PASR on the top level of buddy (eg PASR off
blocks that are free there, and PASR them back on once an
allocation required the block to be broken up)..... that looked the
very most simple to me.

Maybe something much more elaborate is needed, but I didn't see why
so far.

If I understand correctly, you face the same issue that affects
transparent huge pages, but on a much larger scale.  If you have even
one non-moveable allocation in a given top-level buddy block, you
won't be able to PASR that block.

yep we'd use a non-kernel zone for that; not too big a deal.
(the much larger scale you can debate, if your memory controller is
configured correctly the PASR regions are not all that much bigger than
hugepages)

Ah, OK, so you have a very large number of top-level buddy allocations,
then.  Either that or very large hugepages.

quoted

In addition, one of the things that Ankita's patchset is looking to do
is to control allocations in a given region, so that the region can be
easily evacuated.  One use for this is to power off regions of memory,
another is to PASR off regions of memory, and a third is to ensure
that large regions of memory are available for when needed by media
codecs (e.g., cameras), but can be used for other purposes when the
media codecs don't need them (e.g., when viewing photos rather than
taking them).

the codec issue seems to be solved in time; a previous generation
silicon on our (Intel) side had ARM ecosystem blocks that did not do
scatter gather, however the current generation ARM ecosystem blocks all
seem to have added S/G to them....
(in part this is coming from the strong desire to get camera/etc blocks
to all use "GPU texture" class memory, so that the camera can directly
deposit its information into a gpu texture, and similar for media
encode/decode blocks... this avoids copies as well as duplicate memory).

That is indeed a clever approach!

Of course, if the GPU textures are in main memory, there will still
be memory consumption gains to be had as the image size varies (e.g.,
displaying image on one hand vs. menus and UI on the other).  In addition,
I would expect that for quite some time there will continue to be a lot
of systems with display hardware a bit too simple to qualify as "GPU".

							Thanx, Paul