Re: [PATCH RFC v3] mm: Proper document tail pages fields for folio

[David Hildenbrand <david@redhat.com>]

On 16.08.23 20:41, Matthew Wilcox wrote:
> On Wed, Aug 16, 2023 at 03:33:30PM +0200, David Hildenbrand wrote:
>> My simple tests passed so far. If there isn't something obvious missing,
>> I can do more testing and send this as an official patch.
> 
> I think you missed one:
> 
> +++ b/mm/swapfile.c
> @@ -1490,7 +1490,7 @@ int swp_swapcount(swp_entry_t entry)
> 
>          page = vmalloc_to_page(p->swap_map + offset);
>          offset &= ~PAGE_MASK;
> -       VM_BUG_ON(page_private(page) != SWP_CONTINUED);
> +       VM_BUG_ON(page_swap_entry(page).val != SWP_CONTINUED);

That falls under the "weird handling of SWP_CONTINUED using vmalloced 
pages". So different user of page_private().

Note that we don't even store swap entries in there but extended swap 
counts.

> 
>          do {
>                  page = list_next_entry(page, lru);
> 
> I'm not smart enough to understand the use of the one in
> add_swap_count_continuation().  Maybe that also needs to be fixed?

No, that's independent of THP_SWAP, we're not working on the memmap of 
the THP but some weird extension of swap counts.

Thanks for having a look!

-- 
Cheers,

David / dhildenb