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

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Message-ID: <aUwruMji4MCNaOPi@casper.infradead.org>
Date: Wed, 24 Dec 2025 18:06:48 +0000
From: Matthew Wilcox <willy@...radead.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Lance Yang <ioworker0@...il.com>, baolin.wang@...ux.alibaba.com,
	Liam.Howlett@...cle.com, akpm@...ux-foundation.org,
	axelrasmussen@...gle.com, chandna.sahil@...il.com,
	chengming.zhou@...ux.dev, david@...nel.org, david@...hat.com,
	hannes@...xchg.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, lorenzo.stoakes@...cle.com, mhocko@...e.com,
	nphamcs@...il.com, rppt@...nel.org, shakeel.butt@...ux.dev,
	surenb@...gle.com, vbabka@...e.cz, weixugc@...gle.com,
	yosry.ahmed@...ux.dev, yuanchu@...gle.com,
	zhengqi.arch@...edance.com, Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary

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@casper.infradead.org/

which was in v2:

https://lore.kernel.org/linux-mm/f802959f58865371ba1b10081bced98e3784c5e4.1763796152.git.chandna.sahil@gmail.com/