Re: [PATCH] mm: folio_zero_user: open code range computation in folio_zero_user()

[David Hildenbrand (Red Hat)]

On 1/28/26 00:42, Ankur Arora wrote:
> David Hildenbrand (Red Hat) <david@xxxxxxxxxx> 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@xxxxxxxxx>
> > > Closes: https://lore.kernel.org/oe-kbuild-all/202601240453.QCjgGdJa-lkp@xxxxxxxxx/
> > > Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
> > > ---
> > > 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