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

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Message-ID: <62a2d7ba-e7c3-4153-b227-c08802ca9e1c@linux.alibaba.com>
Date: Wed, 24 Dec 2025 15:50:34 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Sahil Chandna <chandna.sahil@...il.com>, akpm@...ux-foundation.org,
 david@...hat.com, lorenzo.stoakes@...cle.com, mhocko@...e.com,
 vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, hannes@...xchg.org,
 shakeel.butt@...ux.dev, zhengqi.arch@...edance.com, Liam.Howlett@...cle.com,
 weixugc@...gle.com, axelrasmussen@...gle.com, yuanchu@...gle.com,
 yosry.ahmed@...ux.dev, nphamcs@...il.com, chengming.zhou@...ux.dev,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: david@...nel.org, Matthew Wilcox <willy@...radead.org>,
 David Laight <david.laight.linux@...il.com>
Subject: Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary
 calculation

Hi Andrew,

On 2025/11/28 15:01, Sahil Chandna wrote:
> Replace hugepage boundary computation with ALIGN() helper instead of
> an open coded expression. This helps to improves code readability.
> 
> This was flagged by Coccinelle (misc/minmax.cocci) as an opportunity
> to use min(), after which the boundary computation was updated following
> review suggestions.
> 
> Found by: make coccicheck MODE=report M=mm/
> No functional change intended.
> 
> Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>
> Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
> Suggested-by: Matthew Wilcox <willy@...radead.org>
> Suggested-by: David Laight <david.laight.linux@...il.com>
> Signed-off-by: Sahil Chandna <chandna.sahil@...il.com>
> ---
>   mm/pagewalk.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 9f91cf85a5be..9fd59d517f37 100644
> --- a/mm/pagewalk.c
> +++ 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.

This patch does introduce functional changes and makes an incorrect 
assumption that the 'end' must be aligned to the hugepage size. However, 
this is not necessarily the case. For example, see how pagemap_read() 
calculates the 'end':

"
end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT);
"

Revert this patch, mm selftests work well.