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SubjectRe: [RFC 2.6.11-rc2-mm2 7/7] mm: manual page migration -- sys_page_migrate
On Mon, Feb 14, 2005 at 10:50:42AM -0800, Dave Hansen wrote:
> On Mon, 2005-02-14 at 07:52 -0600, Robin Holt wrote:
> > The node mask is a list of allowed. This is intended to be as near
> > to a one-to-one migration path as possible.
>
> If that's the case, it would make the kernel internals a bit simpler to
> only take a "from" and "to" node, instead of those maps. You'll end up
> making multiple syscalls, but that shouldn't be a problem.

Then how do you handle overlapping nodes. If I am doing a 5->4, 4->3,
3->2, 2->1 shift in the memory placement and had only a from and to node,
I would end up calling multiple times. This would end up in memory shifting
from 5->4 on the first, 4->3 on the second, ... with the end result of
all memory shifting to a single node.

With the array-of-node maps, you make a single pass across the address
space. This results in a clean mapping without the userspace needing to
know which nodes the pages are on.

On a seperate topic, I would guess the syscall time is trivial compared
to the time to walk the page tables.

Thanks,
Robin
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