Re: [PATCH part1 v6 4/6] x86/mem-hotplug: Support initialize page tables in bottom-up

[Toshi Kani <toshi.kani@hp.com>]

On Fri, 2013-10-04 at 10:00 +0800, Zhang Yanfei wrote:
> From: Tang Chen <tangchen@cn.fujitsu.com>
> 
> The Linux kernel cannot migrate pages used by the kernel. As a
> result, kernel pages cannot be hot-removed. So we cannot allocate
> hotpluggable memory for the kernel.
> 
> In a memory hotplug system, any numa node the kernel resides in
> should be unhotpluggable. And for a modern server, each node could
> have at least 16GB memory. So memory around the kernel image is
> highly likely unhotpluggable.
> 
> ACPI SRAT (System Resource Affinity Table) contains the memory
> hotplug info. But before SRAT is parsed, memblock has already
> started to allocate memory for the kernel. So we need to prevent
> memblock from doing this.
> 
> So direct memory mapping page tables setup is the case. init_mem_mapping()
> is called before SRAT is parsed. To prevent page tables being allocated
> within hotpluggable memory, we will use bottom-up direction to allocate
> page tables from the end of kernel image to the higher memory.
> 
> Acked-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

Acked-by: Toshi Kani <toshi.kani@hp.com>

Thanks,
-Toshi


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