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
