Re: [RFC 00/10] fs/dax: Fix FS DAX page reference counts

Jason Gunthorpe
2024-04-12T11:53:59Z

On Fri, Apr 12, 2024 at 04:55:31PM +1000, Alistair Popple wrote:

> Ok, I think I found the dragons you were talking about earlier for
> device-dax. I completely broke that because as you've already pointed
> out pmd_trans_huge() won't filter out DAX pages. That's fine for FS DAX
> (because the pages are essentially normal pages now anyway), but we
> don't have a PMD equivalent of vm_normal_page() which leads to all sorts
> of issues for DEVDAX.

What about vm_normal_page() depends on the radix level ?

Doesn't DEVDAX memory have struct page too?

> So I will probably have to add something like that unless we only need
> to support large (pmd/pud) mappings of DEVDAX pages on systems with
> CONFIG_ARCH_HAS_PTE_SPECIAL in which case I guess we could just filter
> based on pte_special().

pte_special should only be used by memory without a struct page, is
that what DEVDAX is?

Jason