[PATCH v6 19/26] proc/task_mmu: Mark devdax and fsdax pages as always unpinned

[David Hildenbrand]

On 14.01.25 03:28, Dan Williams wrote:
> Alistair Popple wrote:
>> The procfs mmu files such as smaps and pagemap currently ignore devdax and
>> fsdax pages because these pages are considered special. A future change
>> will start treating these as normal pages, meaning they can be exposed via
>> smaps and pagemap.
>>
>> The only difference is that devdax and fsdax pages can never be pinned for
>> DMA via FOLL_LONGTERM, so add an explicit check in pte_is_pinned() to
>> reflect that.
> 
> I don't understand this patch.


This whole pte_is_pinned() should likely be ripped out (and I have a 
patch here to do that for a long time).

But that's a different discussion.

> 
> pin_user_pages() is also used for Direct-I/O page pinning, so the
> comment about FOLL_LONGTERM is wrong, and I otherwise do not understand
> what goes wrong if the only pte_is_pinned() user correctly detects the
> pin state?

Yes, this patch should likely just be dropped.

Even if folio_maybe_dma_pinned() == true because of "false positives", 
it will behave just like other order-0 pages with false positives, and 
only affect soft-dirty tracking ... which nobody should be caring about 
here at all.

We would always detect the PTE as soft-dirty because we we never
	pte_wrprotect(old_pte)

Yes, nobody should care.

-- 
Cheers,

David / dhildenb