Re: [PATCH v5 4/6] x86/mem-hotplug: Support initialize page tables in bottom-up

From: H. Peter Anvin
Date: Thu Sep 26 2013 - 18:58:18 EST

Can we put this in a common header somewhere?

Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>On Wed, 25 Sep 2013 02:30:51 +0800 Zhang Yanfei
><zhangyanfei.yes@xxxxxxxxx> wrote:
>> From: Tang Chen <tangchen@xxxxxxxxxxxxxx>
>> 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.
>> is called before SRAT is parsed. To prevent page tables being
>> within hotpluggable memory, we will use bottom-up direction to
>> page tables from the end of kernel image to the higher memory.
>> ...
>> + kernel_end = __pa_symbol(_end);
>__pa_symbol() is implemented only on mips and x86.
>I stole the mips implementation like this:
>--- a/mm/memblock.c~a
>+++ a/mm/memblock.c
>@@ -187,8 +187,11 @@ phys_addr_t __init_memblock memblock_fin
> /* avoid allocating the first page */
> start = max_t(phys_addr_t, start, PAGE_SIZE);
> end = max(start, end);
>+#ifdef CONFIG_X86
> kernel_end = __pa_symbol(_end);
>+ kernel_end = __pa(RELOC_HIDE((unsigned long)(_end), 0));
> /*
> * try bottom-up allocation only when bottom-up mode
> * is set and @end is above the kernel image.
>just so I can get a -mm release out the door.

Sent from my mobile phone. Please pardon brevity and lack of formatting.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at