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

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Message-ID: <f1cd2fcc-e3b1-445a-b845-a338ef1f54bc@kernel.org>
Date: Wed, 28 Jan 2026 12:05:57 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: 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] mm: folio_zero_user: open code range computation in
 folio_zero_user()

On 1/28/26 00:42, Ankur Arora wrote:
> 
> David Hildenbrand (Red Hat) <david@...nel.org> writes:
> 
>> 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?
> 
> Yeah, that was a mistake.

Given that we cannot squash and it will be an independent fix, best to 
resend a minimal fix, thanks.

-- 
Cheers

David