Re: [PATCH v2 00/18] Arrange hotpluggable memory as ZONE_MOVABLE.

[Tang Chen]

Hi hpa,

I'm sorry but I don't quite following it.

On 08/05/2013 09:07 PM, H. Peter Anvin wrote:
> On 08/01/2013 12:06 AM, Tang Chen wrote:
> > This patch-set aims to solve some problems at system boot time
> > to enhance memory hotplug functionality.
> >
> > [Background]
> >
> > The Linux kernel cannot migrate pages used by the kernel because
> > of the kernel direct mapping. Since va = pa + PAGE_OFFSET, if the
> > physical address is changed, we cannot simply update the kernel
> > pagetable. On the contrary, we have to update all the pointers
> > pointing to the virtual address, which is very difficult to do.
>
> It does beg the question if that "since" statement should be changed ...

Do you mean we are going to do kernel page migration in the future ?

> we already have it handled differently on Xen PV, but that is kind of
> "special".  There are a whole bunch of other issues with moving kernel
> memory around: you have to worry what might have a physical address
> cached somewhere and what might be in active use and so on...

The current solution is to hotplug ZONE_MOVABLE, which the kernel won't
use. So do you mean if I want to do kernel page migration (which I'm not
doing), I need to worry about what you said above ?

> I am not
> really suggesting it as anything but food for thought at this time.

Sorry for my poor English, and I really cannot understand this one.

Thanks.
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