linux-kernel - Re: [PATCH] mm: folio_zero_user: open code range computation in folio_zero

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Message-ID: <b7549e2a-e5e3-4052-92d9-1e7361b52b78@kernel.org>
Date: Tue, 27 Jan 2026 11:29:58 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, bp@...en8.de, dave.hansen@...ux.intel.com,
 hpa@...or.com, mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
 peterz@...radead.org, tglx@...utronix.de, willy@...radead.org,
 raghavendra.kt@....com, chleroy@...nel.org, ioworker0@...il.com,
 lizhe.67@...edance.com, boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
 kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] mm: folio_zero_user: open code range computation in
 folio_zero_user()

On 1/26/26 19:32, Ankur Arora wrote:
> riscv64-gcc-linux-gnu (v8.5) reports a compile time assert in:
> 
>     r[2] = DEFINE_RANGE(clamp_t(s64, fault_idx - radius, pg.start, pg.end),
>   		       clamp_t(s64, fault_idx + radius, pg.start, pg.end));
> 
> where it decides that pg.start > pg.end in:
>    clamp_t(s64, fault_idx + radius, pg.start, pg.end));
> 
> where pg comes from:
>    const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);
> 
> That does not seem like it could be true. Even for pg.start == pg.end,
> we would need folio_test_large() to evaluate to false at compile time:
> 
>    static inline unsigned long folio_nr_pages(const struct folio *folio)
>    {
> 	if (!folio_test_large(folio))
> 		return 1;
> 	return folio_large_nr_pages(folio);
>    }
> 
> Workaround by open coding the range computation. Also, simplify the type
> declarations for the relevant variables.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202601240453.QCjgGdJa-lkp@intel.com/
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> ---
> 
> Hi Andrew
> 
> I'm not certain about linux-next rebasing protocol, but I'm guessing
> this patch will be squashed in patch-8 ("mm: folio_zero_user: cache
> neighbouring pages").
> 
> The commit message doesn't contain anything needing preserving if it is.
> 
> Thanks
> Ankur
> 
>   mm/memory.c | 23 +++++++++++------------
>   1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index ce933ee4a3dd..e49340f51fa9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -7282,30 +7282,29 @@ static void clear_contig_highpages(struct page *page, unsigned long addr,
>   void folio_zero_user(struct folio *folio, unsigned long addr_hint)
>   {
>   	const unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio));
> -	const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE;
>   	const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1);
> -	const int radius = FOLIO_ZERO_LOCALITY_RADIUS;
> +	const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE;
> +	const long radius = FOLIO_ZERO_LOCALITY_RADIUS;
>   	struct range r[3];
>   	int i;
>   
>   	/*
> -	 * Faulting page and its immediate neighbourhood. Will be cleared at the
> -	 * end to keep its cachelines hot.
> +	 * Faulting page and its immediate neighbourhood. Cleared at the end to
> +	 * keep its cachelines hot.
>   	 */

Why are there rather unrelated changes in this patch? Like this comment 
change, or the movement of "fualt_idx" declaration above?

-- 
Cheers

David