Re: [PATCH v1 2/6] fs/proc/task_mmu: don't indicate PM_MMAP_EXCLUSIVE without PM_PRESENT

Oscar Salvador
2024-06-10T04:38:46Z

On Fri, Jun 07, 2024 at 02:23:53PM +0200, David Hildenbrand wrote:
> Relying on the mapcount for non-present PTEs that reference pages
> doesn't make any sense: they are not accounted in the mapcount, so
> page_mapcount() == 1 won't return the result we actually want to know.
>
> While we don't check the mapcount for migration entries already, we
> could end up checking it for swap, hwpoison, device exclusive, ...
> entries, which we really shouldn't.
>
> There is one exception: device private entries, which we consider
> fake-present (e.g., incremented the mapcount). But we won't care about
> that for now for PM_MMAP_EXCLUSIVE, because indicating PM_SWAP for them
> although they are fake-present already sounds suspiciously wrong.
>
> Let's never indicate PM_MMAP_EXCLUSIVE without PM_PRESENT.

Alternatively we could use is_pfn_swap_entry?
But the PM_PRESENT approach seems more correct.

> Signed-off-by: David Hildenbrand <david@redhat.com>

Signed-off-by: Oscar Salvador <osalvador@suse.de>

--
Oscar Salvador
SUSE Labs