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

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Message-ID: <aGWYrrFJCg219Y8R@x1.local>
Date: Wed, 2 Jul 2025 16:38:06 -0400
From: Peter Xu <peterx@...hat.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Houghton <jthoughton@...gle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Michal Hocko <mhocko@...e.com>,
	David Hildenbrand <david@...hat.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 4/4] mm: Apply vm_uffd_ops API to core mm

On Sun, Jun 29, 2025 at 11:55:27AM +0300, Mike Rapoport wrote:
> On Fri, Jun 27, 2025 at 11:46:55AM -0400, Peter Xu wrote:
> > This patch completely moves the old userfaultfd core to use the new
> > vm_uffd_ops API.  After this change, existing file systems will start to
> > use the new API for userfault operations.
> 
> Maybe:
> 
>   Move userfaultfd core to use new vm_uffd_ops API. After this change file
>   systems that implement vm_operations_struct can start using new API for
>   userfaultfd operations.

Sure.

>  
> > When at it, moving vma_can_userfault() into mm/userfaultfd.c instead,
> > because it's getting too big.  It's only used in slow paths so it shouldn't
> > be an issue.  Move the pte marker check before wp_async, which might be
> > more intuitive because wp_async depends on pte markers.  That shouldn't
> > cause any functional change though because only one check would take effect
> > depending on whether pte marker was selected in config.
> > 
> > This will also remove quite some hard-coded checks for either shmem or
> > hugetlbfs.  Now all the old checks should still work but with vm_uffd_ops.
> > 
> > Note that anonymous memory will still need to be processed separately
> > because it doesn't have vm_ops at all.
> > 
> > Reviewed-by: James Houghton <jthoughton@...gle.com>
> > Signed-off-by: Peter Xu <peterx@...hat.com>
> 
> Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

I'll take this for now, thanks.  We can finish the discussion in patch 1 to
see whether we need to refine the API.

-- 
Peter Xu