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Date: Fri, 27 Mar 2026 10:12:28 +0300
From: Mike Rapoport <rppt@kernel.org>
To: James Houghton <jthoughton@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Hildenbrand <david@kernel.org>,
	Hugh Dickins <hughd@google.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Michal Hocko <mhocko@suse.com>, Muchun Song <muchun.song@linux.dev>,
	Nikita Kalyazin <kalyazin@amazon.com>,
	Oscar Salvador <osalvador@suse.de>,
	Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Shuah Khan <shuah@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, kvm@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 08/15] shmem, userfaultfd: use a VMA callback to
 handle UFFDIO_CONTINUE
Message-ID: <acYt3EA3TCgcgxX-@kernel.org>
References: <20260306171815.3160826-1-rppt@kernel.org>
 <20260306171815.3160826-9-rppt@kernel.org>
 <CADrL8HWLnuQHEPFN9SZbAd_Lq1USJDV=Di4fsQuztwp4v5oXOg@mail.gmail.com>
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In-Reply-To: <CADrL8HWLnuQHEPFN9SZbAd_Lq1USJDV=Di4fsQuztwp4v5oXOg@mail.gmail.com>

Hi James,

On Thu, Mar 26, 2026 at 04:43:27PM -0700, James Houghton wrote:
> On Fri, Mar 6, 2026 at 9:19 AM Mike Rapoport <rppt@kernel.org> wrote:
> >
> > From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> >
> > When userspace resolves a page fault in a shmem VMA with UFFDIO_CONTINUE
> > it needs to get a folio that already exists in the pagecache backing
> > that VMA.
> >
> > Instead of using shmem_get_folio() for that, add a get_folio_noalloc()
> > method to 'struct vm_uffd_ops' that will return a folio if it exists in
> > the VMA's pagecache at given pgoff.
> >
> > Implement get_folio_noalloc() method for shmem and slightly refactor
> > userfaultfd's mfill_get_vma() and mfill_atomic_pte_continue() to support
> > this new API.
> >
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> 
> I found myself asking why HugeTLB wasn't included here; it's because
> we call into hugetlb_mfill_atomic_pte() pretty early. It would be nice
> to have HugeTLB implement get_folio_noalloc() and use the same path as
> shmem, but we don't have to do that now.

You are welcome to join the effort ;-)
 
> Feel free to add:
> 
> Reviewed-by: James Houghton <jthoughton@google.com>

Thanks!
 
-- 
Sincerely yours,
Mike.