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SubjectRe: [PATCH: 002/017]Memory hotplug for new nodes v.4.(change name old add_memory() to arch_add_memory())
> On Tue, 21 Mar 2006 17:08:18 -0800
> Dave Hansen <> wrote:
> > If I missed it before, please refresh my memory. But, if we're
> > providing arch_nid_probe(addr), then why don't we just call it inside of
> > add_memory() on the start address, instead of in the generic code?
> >
> I think just *probe* needs it. The firmware which supports memory-hotplug, ACPI,
> i386/x86_64/ia64, can tell node number as pxm.(proximity domain)
> add_memory() can pass address of paddr as args, but can't pass *pxm*.
> We already maintain pxm <-> nid map. But paddr <-> nid map isn't now.
> If add_memory() doesn't has nid as args, we have to maintain
> (1) pxm <-> nid map.
> (2) paddr <-> nid map.
> Becasue pfn_to_nid() is maintained by SPARSEMEM itself now, *new* paddr<->nid map
> is redundant, I think. And I think the firmware already has the map before calling
> add_memory().

In ACPI's case, kernel has to do 3 steps to get node id from physicall
1) parse DSDT to get device handle of ACPI for new memory.
This step can be described 3 detail steps.
1-1) search memory device in DSDT.
1-2) get _CRS of its memory device to see physicall address.
1-3) compare 1-2)'s address with required paddr.
(its memory device might be for other memory.)
If it is for new memory, then goto step 2),
else goto 1-1) again.
2) get pxm against its device handle.
It is just calling acpi_get_pxm().
3) get node from pxm. If pxm is new one, new node id is assigned.

Step 1) is a bit complicated.
But, when notify of memory hot-add event reaches via ACPI,
its handle is already obtained. So, step 2) and 3) are enough to
get node id. If node id can be passed at add_memory(), that is all.
If not, kernel losts memory device handle information or node id once
at calling add_memory(), and search memory device handle again by step 1).

In addition, if paddr to node id translation is called in add_memory(),
then its code for -each arch- will be like followings.
This will be close from ugly "copy and paste" again....... :-(

nid = paddr_to_node_id(paddr)
if (!node_online(nid)) {
pgdat = hotadd_new_pgdat(nid, start);
if (!pgdat)
return -ENOMEM;


Yasunori Goto

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