[PATCH V4 1/6] mm: Introduce a general RCU get_user_pages_fast.

[David Miller]

From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
Date: Mon, 13 Oct 2014 10:45:24 +0530

> Andrea Arcangeli <aarcange at redhat.com> writes:
> 
>> Hi Steve,
>>
>> On Fri, Sep 26, 2014 at 03:03:48PM +0100, Steve Capper wrote:
>>> This patch provides a general RCU implementation of get_user_pages_fast
>>> that can be used by architectures that perform hardware broadcast of
>>> TLB invalidations.
>>> 
>>> It is based heavily on the PowerPC implementation by Nick Piggin.
>>
>> It'd be nice if you could also at the same time apply it to sparc and
>> powerpc in this same patchset to show the effectiveness of having a
>> generic version. Because if it's not a trivial drop-in replacement,
>> then this should go in arch/arm* instead of mm/gup.c...
> 
> on ppc64 we have one challenge, we do need to support hugepd. At the pmd
> level we can have hugepte, normal pmd pointer or a pointer to hugepage
> directory which is used in case of some sub-architectures/platforms. ie,
> the below part of gup implementation in ppc64
> 
> else if (is_hugepd(pmdp)) {
> 	if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
> 			addr, next, write, pages, nr))
> 		return 0;

Sparc has to deal with the same issue.