linux-kernel - Re: [PATCH v2] mm: madvise: use walk_page_range_vma() instead of walk_page

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Message-ID: <671f8164-a90b-48d7-9446-359eb9493500@arm.com>
Date: Mon, 9 Jun 2025 10:52:47 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Barry Song <21cnbao@...il.com>, linux-mm@...ck.org
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
 Barry Song <v-songbaohua@...o.com>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 David Hildenbrand <david@...hat.com>, Oscar Salvador <osalvador@...e.de>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Suren Baghdasaryan <surenb@...gle.com>, Lokesh Gidra
 <lokeshgidra@...gle.com>, Dev Jain <dev.jain@....com>,
 Tangquan Zheng <zhengtangquan@...o.com>
Subject: Re: [PATCH v2] mm: madvise: use walk_page_range_vma() instead of
 walk_page_range()

On 05/06/2025 09:31, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> We've already found the VMA within madvise_walk_vmas() before calling
> specific madvise behavior functions like madvise_free_single_vma().
> So calling walk_page_range() and doing find_vma() again seems
> unnecessary. It also prevents potential optimizations in those madvise
> callbacks, particularly the use of dedicated per-VMA locking.

FYI it looks like this patch breaks all the guard-region mm selftests with:

# guard-regions.c:719:split_merge:Expected madvise(ptr, 10 * page_size,
MADV_GUARD_INSTALL) (-1) == 0 (0)

Am I the only one that runs these things? :)

[...]

>  mm/madvise.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 

[...]

> @@ -1160,7 +1160,7 @@ static long madvise_guard_install(struct vm_area_struct *vma,
>  		unsigned long nr_pages = 0;
>  
>  		/* Returns < 0 on error, == 0 if success, > 0 if zap needed. */
> -		err = walk_page_range_mm(vma->vm_mm, start, end,
> +		err = walk_page_range_vma(vma, start, end,
>  					 &guard_install_walk_ops, &nr_pages);

IIRC walk_page_range_mm() is an internal API that allows the install_pte()
callback, and the other (public) APIs explicitly disallow it, so presumably
walk_page_range_vma() is now returning an error due to install_pte != NULL?

Thanks,
Ryan

>  		if (err < 0)
>  			return err;
> @@ -1244,7 +1244,7 @@ static long madvise_guard_remove(struct vm_area_struct *vma,
>  	if (!is_valid_guard_vma(vma, /* allow_locked = */true))
>  		return -EINVAL;
>  
> -	return walk_page_range(vma->vm_mm, start, end,
> +	return walk_page_range_vma(vma, start, end,
>  			       &guard_remove_walk_ops, NULL);
>  }
>