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

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Message-ID: <549a60a6-25e2-48d5-b442-49404a857014@lucifer.local>
Date: Fri, 29 Aug 2025 13:51:41 +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>,
        Muchun Song <muchun.song@...ux.dev>, netdev@...r.kernel.org,
        Oscar Salvador <osalvador@...e.de>, Peter Xu <peterx@...hat.com>,
        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 10:51:46PM +0200, David Hildenbrand wrote:
> On 28.08.25 18:57, Lorenzo Stoakes wrote:
> > 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.
>
> I think I'll leave the one in, though, someone should clean up all of them
> in one go.

This is how we always clean these up though, buuut to be fair that's in mm.

>
> Just imagine how the other functions would think about the new guy showing
> off here. :)

;)

>
> >
> > >
> > >   #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?
>
> Yes, reworked it 3 times and messed it up during the last rework. Thanks!

Woot I found an actual bug :P

Yeah it's fiddly so understandable. :)

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo