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. 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>