Re: [PATCH v5 02/18] mm: Define __pte_leaf_size() to also take a PMD entry

Peter Xu
2024-06-11T14:17:43Z

Oscar,

On Tue, Jun 11, 2024 at 11:34:23AM +0200, Oscar Salvador wrote:
> Which means that they would be caught in the following code:
>
> ptl = pmd_huge_lock(pmd, vma);
> if (ptl) {
> - 8MB hugepages will be handled here
> smaps_pmd_entry(pmd, addr, walk);
> spin_unlock(ptl);
> }
> /* pte stuff */
> ...

Just one quick comment: I think there's one challenge though as this is
also not a generic "pmd leaf", but a pgtable page underneath. I think it
means smaps_pmd_entry() won't trivially work here, e.g., it will start to
do this:

if (pmd_present(*pmd)) {
page = vm_normal_page_pmd(vma, addr, *pmd);

Here vm_normal_page_pmd() will only work if pmd_leaf() satisfies its
definition as:

* - It should contain a huge PFN, which points to a huge page larger than
* PAGE_SIZE of the platform. The PFN format isn't important here.

But now it's a pgtable page, containing cont-ptes. Similarly, I think most
pmd_*() helpers will stop working there if we report it as a leaf.

Thanks,

--
Peter Xu