Re: [PATCH v1 20/36] mips: mm: convert __flush_dcache_pages() to __flush_dcache_folio_pages()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Aug 28, 2025 at 12:01:24AM +0200, David Hildenbrand wrote:
> Let's make it clearer that we are operating within a single folio by
> providing both the folio and the page.
>
> This implies that for flush_dcache_folio() we'll now avoid one more
> page->folio lookup, and that we can safely drop the "nth_page" usage.
>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  arch/mips/include/asm/cacheflush.h | 11 +++++++----
>  arch/mips/mm/cache.c               |  8 ++++----
>  2 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/arch/mips/include/asm/cacheflush.h b/arch/mips/include/asm/cacheflush.h
> index 5d283ef89d90d..8d79bfc687d21 100644
> --- a/arch/mips/include/asm/cacheflush.h
> +++ b/arch/mips/include/asm/cacheflush.h
> @@ -50,13 +50,14 @@ extern void (*flush_cache_mm)(struct mm_struct *mm);
>  extern void (*flush_cache_range)(struct vm_area_struct *vma,
>  	unsigned long start, unsigned long end);
>  extern void (*flush_cache_page)(struct vm_area_struct *vma, unsigned long page, unsigned long pfn);
> -extern void __flush_dcache_pages(struct page *page, unsigned int nr);
> +extern void __flush_dcache_folio_pages(struct folio *folio, struct page *page, unsigned int nr);

NIT: Be good to drop the extern.

>
>  #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
>  static inline void flush_dcache_folio(struct folio *folio)
>  {
>  	if (cpu_has_dc_aliases)
> -		__flush_dcache_pages(&folio->page, folio_nr_pages(folio));
> +		__flush_dcache_folio_pages(folio, folio_page(folio, 0),
> +					   folio_nr_pages(folio));
>  	else if (!cpu_has_ic_fills_f_dc)
>  		folio_set_dcache_dirty(folio);
>  }
> @@ -64,10 +65,12 @@ static inline void flush_dcache_folio(struct folio *folio)
>
>  static inline void flush_dcache_page(struct page *page)
>  {
> +	struct folio *folio = page_folio(page);
> +
>  	if (cpu_has_dc_aliases)
> -		__flush_dcache_pages(page, 1);
> +		__flush_dcache_folio_pages(folio, page, folio_nr_pages(folio));

Hmmm, shouldn't this be 1 not folio_nr_pages()? Seems that the original
implementation only flushed a single page even if contained within a larger
folio?

>  	else if (!cpu_has_ic_fills_f_dc)
> -		folio_set_dcache_dirty(page_folio(page));
> +		folio_set_dcache_dirty(folio);
>  }
>
>  #define flush_dcache_mmap_lock(mapping)		do { } while (0)
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index bf9a37c60e9f0..e3b4224c9a406 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -99,9 +99,9 @@ SYSCALL_DEFINE3(cacheflush, unsigned long, addr, unsigned long, bytes,
>  	return 0;
>  }
>
> -void __flush_dcache_pages(struct page *page, unsigned int nr)
> +void __flush_dcache_folio_pages(struct folio *folio, struct page *page,
> +		unsigned int nr)
>  {
> -	struct folio *folio = page_folio(page);
>  	struct address_space *mapping = folio_flush_mapping(folio);
>  	unsigned long addr;
>  	unsigned int i;
> @@ -117,12 +117,12 @@ void __flush_dcache_pages(struct page *page, unsigned int nr)
>  	 * get faulted into the tlb (and thus flushed) anyways.
>  	 */
>  	for (i = 0; i < nr; i++) {
> -		addr = (unsigned long)kmap_local_page(nth_page(page, i));
> +		addr = (unsigned long)kmap_local_page(page + i);
>  		flush_data_cache_page(addr);
>  		kunmap_local((void *)addr);
>  	}
>  }
> -EXPORT_SYMBOL(__flush_dcache_pages);
> +EXPORT_SYMBOL(__flush_dcache_folio_pages);
>
>  void __flush_anon_page(struct page *page, unsigned long vmaddr)
>  {
> --
> 2.50.1
>