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SubjectRe: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory
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Hi Tang,
On Fri, 2013-02-01 at 09:57 +0800, Tang Chen wrote:
> On 02/01/2013 09:36 AM, Simon Jeons wrote:
> > On Fri, 2013-02-01 at 09:32 +0800, Jianguo Wu wrote:
> >>>
> >>> So if config NUMA, kernel memory will not be linear mapping anymore? For
> >>> example,
> >>>
> >>> Node 0 Node 1
> >>>
> >>> 0 ~ 10G 11G~14G
>
> It has nothing to do with linear mapping, I think.
>
> >>>
> >>> kernel memory only at Node 0? Can part of kernel memory also at Node 1?
>
> Please refer to find_zone_movable_pfns_for_nodes().

I see, thanks. :)

> The kernel is not only on node0. It uses all the online nodes evenly. :)
>
> >>>
> >>> How big is kernel direct mapping memory in x86_64? Is there max limit?
> >>
> >>
> >> Max kernel direct mapping memory in x86_64 is 64TB.
> >
> > For example, I have 8G memory, all of them will be direct mapping for
> > kernel? then userspace memory allocated from where?
>
> I think you misunderstood what Wu tried to say. :)
>
> The kernel mapped that large space, it doesn't mean it is using that
> large space.
> The mapping is to make kernel be able to access all the memory, not for
> the kernel
> to use only. User space can also use the memory, but each process has
> its own mapping.
>
> For example:
>
> 64TB, what ever
> xxxTB, what ever
> logic address space: |_____kernel_______|_________user_________________|
> \ \ / /
> \ /\ /
> physical address space: |___\/__\/_____________| 4GB or
> 8GB, what ever
> *****

How much address space user process can have on x86_64? Also 8GB?

>
> The ***** part physical is mapped to user space in the process' own
> pagetable.
> It is also direct mapped in kernel's pagetable. So the kernel can also
> access it. :)

But how to protect user process not modify kernel memory?

>
> >
> >>
> >>> It seems that only around 896MB on x86_32.
> >>>
> >>>>
> >>>> We need firmware take part in, such as SRAT in ACPI BIOS, or the firmware
> >>>> based memory migration mentioned by Liu Jiang.
> >>>
> >>> Is there any material about firmware based memory migration?
>
> No, I don't have any because this is a functionality of machine from HUAWEI.
> I think you can ask Liu Jiang or Wu Jianguo to share some with you. :)
>
> Thanks. :)




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