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

H. Peter Anvin
2013-08-05T13:08:53Z

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

-hpa