Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary

[David Laight]

On Thu, 25 Dec 2025 10:32:46 +0100
"David Hildenbrand (Red Hat)" <david@xxxxxxxxxx> wrote:

> On 12/24/25 19:06, Matthew Wilcox wrote:
> > On Wed, Dec 24, 2025 at 02:08:29PM +0000, David Laight wrote:  
> >>>>> +++ b/mm/pagewalk.c
> >>>>> @@ -312,8 +312,7 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
> >>>>>    static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
> >>>>>    				       unsigned long end)
> >>>>>    {
> >>>>> -	unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
> >>>>> -	return boundary < end ? boundary : end;
> >>>>> +	return min(ALIGN(addr, huge_page_size(h)), end);
> >>>>>    }  
> >>>>
> >>>> Please drop this patch from the mm-new branch, as it causes
> >>>> 'run_vmtests.sh' to hang. Specifically, it leads to the system hanging
> >>>> when executing hugepage-vmemmap test, because the program falls into an
> >>>> infinite loop in walk_hugetlb_range() and cannot break out.  
> >>>
> >>> Good catch! The problem is that ALIGN() returns addr itself when already
> >>> aligned, causing the infinite loop ...  
> >>
> >> Using ALIGN(addr + 1, huge_page_size(h)) would work.
> >> Although it could be (addr + 1) & ~huge_page_mask(h) which is probably
> >> the easiest to understand.
> >> Some of the 'helper' macros don't really make the code easier to read.
> >> (And that includes a lot of uses of min().)  
> > 
> > Or we could go back to my original suggestion.
> > 
> > https://lore.kernel.org/linux-mm/aRyOWrARRlUCeEz6@xxxxxxxxxxxxxxxxxxxx/
> > 
> > which was in v2:
> > 
> > https://lore.kernel.org/linux-mm/f802959f58865371ba1b10081bced98e3784c5e4.1763796152.git.chandna.sahil@xxxxxxxxx/  
> 
> I'm starting to wonder whether we should just leave that code alone :)
> 

Maybe 'we' should stop checkpatch (etc) suggesting min() in trivial
cases. It doesn't really make the code better.

	David