Re: [PATCH v2 12/13] mm: Add tail private fields to struct folio

[David Hildenbrand <david@redhat.com>]

On 16.08.23 17:12, Matthew Wilcox (Oracle) wrote:
> Because THP_SWAP uses page->private for each page, we must not use
> the space which overlaps that field for anything which would conflict
> with that.  We avoid the conflict on 32-bit systems by disallowing
> THP_SWAP on 32-bit.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>   include/linux/mm_types.h | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 659c7b84726c..3880b3f2e321 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -340,8 +340,11 @@ struct folio {
>   			atomic_t _pincount;
>   #ifdef CONFIG_64BIT
>   			unsigned int _folio_nr_pages;
> -#endif
> +			/* 4 byte gap here */
>   	/* private: the union with struct page is transitional */
> +			/* Fix THP_SWAP to not use tail->private */
> +			unsigned long _private_1;

If you could give

https://lkml.kernel.org/r/b887e764-ffa3-55ee-3c44-69cb15f8a115@redhat.com

a quick glimpse to see if anything important jumps at you, that would be 
great.

That really should be fixed.

-- 
Cheers,

David / dhildenb