Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros

[Steven Price]

On 21/02/2019 14:28, Kirill A. Shutemov wrote:
> On Thu, Feb 21, 2019 at 11:34:52AM +0000, Steven Price wrote:
>> From: James Morse <james.morse@xxxxxxx>
>>
>> Exposing the pud/pgd levels of the page tables to walk_page_range() means
>> we may come across the exotic large mappings that come with large areas
>> of contiguous memory (such as the kernel's linear map).
>>
>> For architectures that don't provide p?d_large() macros, provided a
>> does nothing default.
> 
> Nak, sorry.
> 
> Power will get broken by the patch. It has pmd_large() inline function,
> that will be overwritten by the define from this patch.
> 
> I believe it requires more ground work on arch side in general.
> All architectures that has huge page support has to provide these helpers
> (and matching defines) before you can use it in a generic code.

Sorry about that, I had compile tested on power, but obviously not the
right config to actually see the breakage.

I'll do some grepping - hopefully this is just a case of exposing the
functions/defines that already exist for those architectures.

Note that in terms of the new page walking code, these new defines are
only used when walking a page table without a VMA (which isn't currently
done), so architectures which don't use p?d_large currently will work
fine with the generic versions. They only need to provide meaningful
definitions when switching to use the walk-without-a-VMA functionality.

Thanks for reporting the breakage.

Steve