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
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