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

Commit Message

Andrew Morton Sept. 26, 2013, 10:52 p.m. UTC

On Wed, 25 Sep 2013 02:30:51 +0800 Zhang Yanfei <[e-mail]> wrote:

> From: Tang Chen <[e-mail]>
> 
> 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.
> 
> ...
>
> +		kernel_end = __pa_symbol(_end);

__pa_symbol() is implemented only on mips and x86.

I stole the mips implementation like this:


just so I can get a -mm release out the door.
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Comments

H. Peter Anvin Sept. 26, 2013, 10:57 p.m. UTC | #1

Can we put this in a common header somewhere?

Andrew Morton <[e-mail]> wrote:
>On Wed, 25 Sep 2013 02:30:51 +0800 Zhang Yanfei
><[e-mail]> wrote:
>
>> From: Tang Chen <[e-mail]>
>> 
>> 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.
>> 
>> ...
>>
>> +		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);
>-
>+#else
>+	kernel_end = __pa(RELOC_HIDE((unsigned long)(_end), 0));
>+#endif
> 	/*
> 	 * 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.

Patch

--- 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);
-
+#else
+	kernel_end = __pa(RELOC_HIDE((unsigned long)(_end), 0));
+#endif
 	/*
 	 * try bottom-up allocation only when bottom-up mode
 	 * is set and @end is above the kernel image.