Re: [PATCH 5/6] mm/mremap: Use pmd/pud_poplulate to update page table entries
From: Christophe Leroy <hidden>
Date: 2021-06-14 05:27:27
Also in:
linux-mm
Le 13/06/2021 à 13:13, Aneesh Kumar K.V a écrit :
On 6/13/21 4:20 PM, Matthew Wilcox wrote:quoted
On Sun, Jun 13, 2021 at 02:36:13PM +0530, Aneesh Kumar K.V wrote:quoted
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