linux-kernel - Re: [PATCH v2 5/5] mm/mmu_gather: Store and process pages in contig ranges

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Message-ID: <ZO9bGbsrveOIyeAA@casper.infradead.org>
Date:   Wed, 30 Aug 2023 16:07:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Ryan Roberts <ryan.roberts@....com>
Cc:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        David Hildenbrand <david@...hat.com>,
        Yu Zhao <yuzhao@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] mm/mmu_gather: Store and process pages in contig
 ranges

On Wed, Aug 30, 2023 at 10:50:11AM +0100, Ryan Roberts wrote:
> +++ b/include/asm-generic/tlb.h
> @@ -246,11 +246,11 @@ struct mmu_gather_batch {
>  	struct mmu_gather_batch	*next;
>  	unsigned int		nr;
>  	unsigned int		max;
> -	struct page		*pages[];
> +	struct pfn_range	folios[];

I think it's dangerous to call this 'folios' as it lets you think that
each entry is a single folio.  But as I understand this patch, you can
coagulate contiguous ranges across multiple folios.

> -void free_pages_and_swap_cache(struct page **pages, int nr)
> +void free_folios_and_swap_cache(struct pfn_range *folios, int nr)
>  {
>  	lru_add_drain();
>  	for (int i = 0; i < nr; i++)
> -		free_swap_cache(pages[i]);
> -	release_pages(pages, nr);
> +		free_swap_cache(pfn_to_page(folios[i].start));

... but here, you only put the swapcache for the first folio covered by
the range, not for each folio.

> +	folios_put_refs(folios, nr);

It's kind of confusing to have folios_put() which takes a struct folio *
and then folios_put_refs() which takes a struct pfn_range *.
pfn_range_put()?