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Subject: Re: [PATCH] powerpc/mm: Lockless get_user_pages_fast()
Date: Wed, 30 Jul 2008 17:35:57 -0500
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On Jul 30, 2008, at 5:26 PM, Benjamin Herrenschmidt wrote:

>
>>> Index: linux-work/arch/powerpc/Kconfig
>>> ===================================================================
>>> --- linux-work.orig/arch/powerpc/Kconfig	2008-07-30
>>> 13:17:06.000000000 +1000
>>> +++ linux-work/arch/powerpc/Kconfig	2008-07-30 13:27:40.000000000
>>> +1000
>>> @@ -42,6 +42,9 @@ config GENERIC_HARDIRQS
>>> 	bool
>>> 	default y
>>>
>>> +config HAVE_GET_USER_PAGES_FAST
>>> +	def_bool PPC64
>>> +
>>> config HAVE_SETUP_PER_CPU_AREA
>>> 	def_bool PPC64
>>
>> what's ppc64 specific here?
>
> Mostly _PAGE_SPECIAL (which I do plan to add to embedded which is why
> I've been trying hard to free a PTE bit :-) and the way we synchronize
> with the freeing of page tables (ppc64 uses RCU, ppc32 doesn't, we'd
> have to find something to keep fast gup in sync).

I think we have some code that uses RCU for page freeing.  I'll dig it  
up and posted it.

- k