Re: [PATCH 00/10] mm: Linux VM Infrastructure to support MemoryPower Management

[david]

On Thu, 7 Jul 2011, Pekka Enberg wrote:

> On Wed, 6 Jul 2011, Pekka Enberg wrote:
> > > Why does the allocator need to know about address boundaries? Why
> > > isn't it enough to make the page allocator and reclaim policies favor 
> > > using
> > > memory from lower addresses as aggressively as possible? That'd mean
> > > we'd favor the first memory banks and could keep the remaining ones
> > > powered off as much as possible.
> > >
> > > IOW, why do we need to support scenarios such as this:
> > >
> > >   bank 0     bank 1   bank 2    bank3
> > > | online  | offline | online  | offline |
> On Wed, 6 Jul 2011, david@xxxxxxx wrote:
> > I believe that there are memory allocations that cannot be moved after they 
> > are made (think about regions allocated to DMA from hardware where the 
> > hardware has already been given the address space to DMA into)
> >
> > As a result, you may not be able to take bank 2 offline, so your option is 
> > to either leave banks 0-2 all online, or support emptying bank 1 and taking 
> > it offline.
>
> But drivers allocate DMA memory for hardware during module load and stay 
> pinned there until the driver is unloaded, no? So in practice DMA buffers are 
> going to be in banks 0-1?

that depends on when the device was initialized. it is common for them to 
be in the beginning, but with hotplug, who knows.

David Lang
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/