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

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Message-ID: <2be7db96-2fa2-4348-837e-648124bd604f@redhat.com>
Date: Thu, 28 Aug 2025 22:51:46 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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>,
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Subject: Re: [PATCH v1 20/36] mips: mm: convert __flush_dcache_pages() to
 __flush_dcache_folio_pages()

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.

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!

-- 
Cheers

David / dhildenb