linux-kernel - Re: [PATCH v1 20/36] mips: mm: convert __flush_dcache_pages() to __flush_dcache_folio

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Message-ID: <ea74f0e3-bacf-449a-b7ad-213c74599df1@lucifer.local>
Date: Thu, 28 Aug 2025 17:57:01 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        Christoph Lameter <cl@...two.org>, Dennis Zhou <dennis@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, iommu@...ts.linux.dev,
        io-uring@...r.kernel.org, Jason Gunthorpe <jgg@...dia.com>,
        Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
        John Hubbard <jhubbard@...dia.com>, kasan-dev@...glegroups.com,
        kvm@...r.kernel.org, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arm-kernel@...s.com, linux-arm-kernel@...ts.infradead.org,
        linux-crypto@...r.kernel.org, linux-ide@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-mm@...ck.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-scsi@...r.kernel.org, Marco Elver <elver@...gle.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michal Hocko <mhocko@...e.com>, Mike Rapoport <rppt@...nel.org>,
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        Robin Murphy <robin.murphy@....com>,
        Suren Baghdasaryan <surenb@...gle.com>, Tejun Heo <tj@...nel.org>,
        virtualization@...ts.linux.dev, Vlastimil Babka <vbabka@...e.cz>,
        wireguard@...ts.zx2c4.com, x86@...nel.org, Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v1 20/36] mips: mm: convert __flush_dcache_pages() to
 __flush_dcache_folio_pages()

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@...ha.franken.de>
> Signed-off-by: David Hildenbrand <david@...hat.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
>