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

From: Tang Chen
Date: Mon Aug 05 2013 - 09:39:58 EST

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.


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.

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