[PATCH] powerpc/powernv: Increase memory block size to 1GB on radix

[Michael Ellerman]

We should do the 1G block size as a fix, and backport it, and then make the hot unplug code smarter.

cheers

On 8 September 2017 11:15:47 am AEST, Anton Blanchard <anton at ozlabs.org> wrote:
>Hi Reza,
>
>> I may be misunderstanding this, but what if we did something like x86
>
>> does? When trying to unplug a region smaller than the mapping, they
>> fill that part of the pagetable with 0xFD instead of freeing the
>> whole thing. Once the whole thing is 0xFD, free it.
>> 
>> See arch/x86/mm/init_64.c:remove_{pte,pmd,pud}_table()
>> 
>> ---%<---
>> 	memset((void *)addr, PAGE_INUSE, next - addr);
>> 
>> 	page_addr = page_address(pte_page(*pte));
>> 	if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) {
>> 		...
>> 		pte_clear(&init_mm, addr, pte);
>> 		...
>> 	}
>> ---%<---
>
>But you only have 1GB ptes at this point, you'd need to start
>instantiating a new level in the tree, and populate 2MB ptes.
>
>That is what Ben is suggesting. I'm happy to go any way (fix hotplug
>to handle this, or increase the memblock size on PowerNV to 1GB), I
>just
>need a solution.
>
>Anton

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