linux-kernel - Re: [PATCH v3] mm: folio_zero_user: open code range computation in folio_zero

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Message-ID: <9717eaea-9bbd-4612-bc45-c7f85fe1ba67@kernel.org>
Date: Sat, 7 Feb 2026 11:10:00 +0100
From: "David Hildenbrand (Arm)" <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 v3] mm: folio_zero_user: open code range computation in
 folio_zero_user()

On 2/6/26 23:38, 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/
> Fixes: 93552c9a3350 ("mm: folio_zero_user: cache neighbouring pages")
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> Acked-by: David Hildenbrand (Arm) <david@...nel.org>
> ---
> 
> Hi Andrew
> 

Thanks Amkur and hoping you'll have a nice weekend!

-- 
Cheers,

David