linux-kernel - Re: [PATCH v2 1/4] mm: Introduce vm_uffd

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Message-ID: <aMp-kW3OLqtZs8sh@kernel.org>
Date: Wed, 17 Sep 2025 12:25:37 +0300
From: Mike Rapoport <rppt@...nel.org>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>,
	Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
	Muchun Song <muchun.song@...ux.dev>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Houghton <jthoughton@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Ujwal Kundur <ujwal.kundur@...il.com>
Subject: Re: [PATCH v2 1/4] mm: Introduce vm_uffd_ops API

Hi Liam,

On Mon, Sep 08, 2025 at 12:53:37PM -0400, Liam R. Howlett wrote:
> 
> Reading through the patches, I'm not entirely sure what you are
> proposing.
> 
> What I was hoping to see by a generalization of the memory types is a
> much simpler shared code base until the code hit memory type specific
> areas where a function pointer could be used to keep things from getting
> complicated (or, I guess a switch statement..).
> 
> What we don't want is non-mm code specifying values for the function
> pointer and doing what they want, or a function pointer that returns a
> core mm resource (in the old example this was a vma, here it is a
> folio).
> 
> From this patch set:
> +        * Return: zero if succeeded, negative for errors.
> +        */
> +       int (*uffd_get_folio)(struct inode *inode, pgoff_t pgoff,
> +                             struct folio **folio);
> 
> This is one of the contention points in the current scenario as the
> folio would be returned.

I don't see a problem with it. It's not any different from
vma_ops->fault(): a callback for a filesystem to get a folio that will be
mapped afterwards by the mm code.

-- 
Sincerely yours,
Mike.