Re: [v4][PATCH 2/2] fix large pages in pagemap

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 11 Jun 2008 13:34:22 -0700
Dave Hansen <dave@linux.vnet.ibm.com> wrote:

> On Wed, 2008-06-11 at 13:11 -0700, Andrew Morton wrote:
> > Really?  There already a couple of pmd_huge() tests in mm/memory.c and
> > Rik's access_process_vm-device-memory-infrastructure.patch adds
> > another one.
> 
> We're not supposed to ever hit the one in follow_page() because there
> are:
> 
>                 if (is_vm_hugetlb_page(vma)) {
>                         i = follow_hugetlb_page(mm, vma, pages, vmas,
>                                                 &start, &len, i, write);
>                         continue;
>                 }
> 
> checks before them like in get_user_pages();
> 
> The other mm/memory.c call is under alloc_vm_area(), and that's
> supposedly only used on kernel addresses.  I don't think we even have
> Linux pagetables for kernel addresses on ppc.
> 

access_process_vm-device-memory-infrastructure.patch is a powerpc
feature, and it uses pmd_huge().

Am I missing something, or is pmd_huge() a whopping big grenade for x86
developers to toss at non-x86 architectures?  It seems quite dangerous.

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