[PATCH 5/6] mm/mremap: Use pmd/pud_poplulate to update page table entries

[Christophe Leroy]

Le 13/06/2021 à 13:13, Aneesh Kumar K.V a écrit :
> On 6/13/21 4:20 PM, Matthew Wilcox wrote:
>> On Sun, Jun 13, 2021 at 02:36:13PM +0530, Aneesh Kumar K.V wrote:
>>> IIUC the reason why we do have pmd_pgtable() is that pgtable_t type
>>> is arch dependent. On some architecture it is pte_t * and on the other
>>> struct page *. The reason being highmem and level 4 page table can
>>> be located in highmem.
>>
>> That is ahistorical.  See 2f569afd9ced9ebec9a6eb3dbf6f83429be0a7b4 --
>> we have pgtable_t for the benefit of s390's crazy sub-page page table
>> sizes.
> 
> That is also true with ppc64. We do sub-page page table size. I was trying to explain why it can't 
> be pte_t * everywhere and why we have
> it as struct page *.

ppc32 as well. On the 8xx, with 16k size pages, the HW still use 4k page tables, so we do use sub-pages.

In order too keep the code simple, we have converted all powerpc to sub-pages for that, allthough 
some powerpc platforms have only one sub-page per page.

Christophe