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

Linus Torvalds [off-list ref] writes:

On Thu, Jun 10, 2021 at 1:36 AM Aneesh Kumar K.V
[off-list ref] wrote:

quoted

@@ -306,8 +306,7 @@ static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr,

        VM_BUG_ON(!pud_none(*new_pud));

-       /* Set the new pud */
-       set_pud_at(mm, new_addr, new_pud, pud);
+       pud_populate(mm, new_pud, (pmd_t *)pud_page_vaddr(pud));
        flush_tlb_range(vma, old_addr, old_addr + PUD_SIZE);
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);

That "(pmd_t *)pud_page_vaddr(pud)" looks a bit odd and doesn't match
the pattern.

Should we perhaps have a wrapper for it? Maybe called "pud_pgtable()",
the same way we have pmd_pgtable()?

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. 

The above is not true with the level 3 table and hence we didn't add an
extra type to point to level 3 table.

We could add pud_pgtable(), but then it will essentially be a typecast
as I did above?

Even if we want to do that, that should be done as a separate patch than
this series?

And that wrapper would be good to have a comment or two about what it
actually is. The same way that pmd_pgtable() should but doesn't ;(

            Linus