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

From: H. Peter Anvin
Date: Mon Aug 05 2013 - 09:08:57 EST

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.


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