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

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Message-ID: <87zf5ibu4f.fsf@oracle.com>
Date: Sun, 08 Feb 2026 17:09:20 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: "David Hildenbrand (Arm)" <david@...nel.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, 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()


David Hildenbrand (Arm) <david@...nel.org> writes:

> 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!

Thanks and to you too (or at least what's left of it) :).

--
ankur