[RFC] hotplug memory remove - walk_memory_resource for ppc64

[KAMEZAWA Hiroyuki]

On Tue, 30 Oct 2007 11:19:11 -0800
Badari Pulavarty <pbadari at us.ibm.com> wrote:

> Hi KAME,
> 
> As I mentioned while ago, ppc64 does not export information about
> "system RAM" in /proc/iomem. Looking at the code and usage
> scenerios I am not sure what its really serving. Could you 
> explain what its purpose & how the range can be invalid ?
> 
Hm, I added walk_memory_resource() for hot-add, at first.

Size of memory section is fixed and just depend on architecture, but
any machine can have any memory-hole within continuous memory-section-size
range of physical memory. Then we have to detect which page can be
target of online_page() and which are leaved as Reserved.

ioresource was good structure for remembering "which memory is conventional
memory" and i386/x86_64/ia64 registered conventional memory as "System RAM",
when I posted patch. (just say "System Ram" is not for memory hotplug.)

I used walk_memory_resource() again in memory hotremove.

(If I rememember correctly, walk_memory_resouce() helps x86_64 memory hot-add.
 than our ia64 box.
 In our ia64 box, we do node-hotadd. Section size is 1GiB and it has some
 "for firmware" area in newly-added node.)

> At least on ppc64, all the memory ranges we get passed comes from
> /sysfs memblock information and they are guaranteed to match 
> device-tree entries. On ppc64, each 16MB chunk has a /sysfs entry
> and it will be part of the /proc/device-tree entry. Since we do
> "online" or "offline" to /sysfs entries to add/remove pages - 
> these ranges are guaranteed to be valid.
> 
ok.

> Since this check is redundant for ppc64, I propose following patch.
> Is this acceptable ? If some one really really wants, I can code
> up this to walk lmb or /proc/device-tree and verify the range &
> adjust the entries for overlap (I don't see how that can happen).
> 
ok. If ppc64 guarantees "there is no memory hole in section", please try.
I have no objection.
I just would like to ask to add some text to explain
"ppc64 doesn't need to care memory hole in a section."


Thanks,
-Kame