linux-kernel - Re: [RFC PATCH 3/3] mm/mincore: avoid touching the PTL

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Message-ID: <2d84e83e-5fca-402b-a01d-811003c2551e@redhat.com>
Date: Mon, 11 Aug 2025 10:41:02 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>, Matthew Wilcox <willy@...radead.org>,
 Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>,
 Barry Song <baohua@...nel.org>, Baoquan He <bhe@...hat.com>,
 Nhat Pham <nphamcs@...il.com>, Kemeng Shi <shikemeng@...weicloud.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] mm/mincore: avoid touching the PTL

On 07.08.25 17:27, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> mincore only interested in the existence of a page, which is a
> changing state by nature, locking and making it stable is not needed.
> And now neither mincore_page or mincore_swap requires PTL, this PTL
> locking can be dropped.
> 
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
>   mm/mincore.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mincore.c b/mm/mincore.c
> index 1ac53acac239..cc4460aba1f9 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -153,13 +153,13 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>   		goto out;
>   	}
>   
> -	ptep = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> +	ptep = pte_offset_map(pmd, addr);

I agree with Jann, that if we move away from the PTL, we better have a 
very good reason (+performance numbers).

-- 
Cheers,

David / dhildenb