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SubjectRe: [Lhms-devel] [PATCH 1/10] hot-add-mem x86_64: acpi motherboard fix
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On Tue, 2006-08-08 at 09:31 +0900, KAMEZAWA Hiroyuki wrote:
> On Mon, 07 Aug 2006 11:39:27 -0700
> keith mannthey <kmannth@us.ibm.com> wrote:
>
> > On Sat, 2006-08-05 at 14:51 +0900, KAMEZAWA Hiroyuki wrote:
> > > On Fri, 4 Aug 2006 07:13:51 -0600
> > > Keith Mannthey <kmannth@us.ibm.com> wrote:
> > > > I have worked to integrate the feedback I recived on the last round of patches
> > > > and welcome more ideas/advice. Thanks to everyone who has provied input on
> > > > these patches already.
> > > >
> > > Just from review...
> > >
> > > If new zone , which was empty at boot, are added into the system.
> > > build_all_zonelists() has to be called. (see online_pages() in memory_hotplug.c)
> > > it looks x86_64's __add_pages() doesn't calles it.
> >
> > With RESERVE there are not empty zones. All zones (including add-areas)
> > are setup during boot and hot add areas reserved in the bootmem
> > allocator.
> >
> > Zones don't change size there is no adding to the zone just on-lining on
> > pages at are already present in the zone.
> >
> Hmm, curious.
> please explain.
> ==
> int __add_pages(struct zone *z, unsigned long start_pfn, unsigned long nr_pages)
> {
> int err = -EIO;
> unsigned long pfn;
> unsigned long total = 0, mem = 0;
> for (pfn = start_pfn; pfn < start_pfn + nr_pages; pfn++) {
> if (pfn_valid(pfn)) {
> online_page(pfn_to_page(pfn));
> err = 0;
> mem++;
> }
> total++;
> }
> if (!err) {
> z->spanned_pages += total;
> z->present_pages += mem; -------------------------------(*)

It is an accounting issue. What I meant by re-sizing is there is no
change to node_mem_map (with reserve CONFIG_FLAT_NODE_MEM_MAP is set).
When the original size for the zone is setup it views that add areas as
a "hole" in the e820 space.

See arch/x86_64/mm/init.c size_zones.

> ==
> It looks contents of zone is increased at (*). Do I see old code ?
>
> ==
> static inline int populated_zone(struct zone *zone)
> {
> return (!!zone->present_pages);
> }
> ==
> "empty zone" I said means a zone which is not populated.

I know of no x86_64 hardware the supports empty node hot-add memory. If
it exists I would recommend using SPARSEMEM based hot-add. On HW I am
aware of there is always some memory present in a node at boot.


Thanks,
Keith

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