Re: [PATCH v4 1/4] mm/mmu_notifier: Allow two-pass struct mmu_interval_notifiers

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Replying to list address for reference.

On Fri, 2026-03-06 at 14:11 +0100, David Hildenbrand (Arm) wrote:
> On 3/6/26 14:05, Thomas Hellström wrote:
> > On Thu, 2026-03-05 at 15:00 +0100, David Hildenbrand (Arm) wrote:
> > > On 3/5/26 10:39, Thomas Hellström wrote:
> > > > GPU use-cases for mmu_interval_notifiers with hmm often involve
> > > > starting a gpu operation and then waiting for it to complete.
> > > > These operations are typically context preemption or TLB
> > > > flushing.
> > > > 
> > > > With single-pass notifiers per GPU this doesn't scale in
> > > > multi-gpu scenarios. In those scenarios we'd want to first
> > > > start
> > > > preemption- or TLB flushing on all GPUs and as a second pass
> > > > wait
> > > > for them to complete.
> > > > 
> > > > One can do this on per-driver basis multiplexing per-driver
> > > > notifiers but that would mean sharing the notifier "user" lock
> > > > across all GPUs and that doesn't scale well either, so adding
> > > > support
> > > > for multi-pass in the core appears to be the right choice.
> > > > 
> > > > Implement two-pass capability in the mmu_interval_notifier. Use
> > > > a
> > > > linked list for the final passes to minimize the impact for
> > > > use-cases that don't need the multi-pass functionality by
> > > > avoiding
> > > > a second interval tree walk, and to be able to easily pass data
> > > > between the two passes.
> > > > 
> > > > v1:
> > > > - Restrict to two passes (Jason Gunthorpe)
> > > > - Improve on documentation (Jason Gunthorpe)
> > > > - Improve on function naming (Alistair Popple)
> > > > v2:
> > > > - Include the invalidate_finish() callback in the
> > > >   struct mmu_interval_notifier_ops.
> > > > - Update documentation (GitHub Copilot:claude-sonnet-4.6)
> > > > - Use lockless list for list management.
> > > > v3:
> > > > - Update kerneldoc for the struct
> > > > mmu_interval_notifier_finish::list member
> > > >   (Matthew Brost)
> > > > - Add a WARN_ON_ONCE() checking for NULL invalidate_finish() op
> > > > if
> > > >   if invalidate_start() is non-NULL. (Matthew Brost)
> > > > v4:
> > > > - Addressed documentation review comments by David Hildenbrand.
> > > > 
> > > > Cc: Matthew Brost <matthew.brost@intel.com>
> > > > Cc: Christian König <christian.koenig@amd.com>
> > > > Cc: David Hildenbrand <david@kernel.org>
> > > > Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > > > Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
> > > > Cc: Vlastimil Babka <vbabka@kernel.org>
> > > > Cc: Mike Rapoport <rppt@kernel.org>
> > > > Cc: Suren Baghdasaryan <surenb@google.com>
> > > > Cc: Michal Hocko <mhocko@suse.com>
> > > > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > > Cc: Simona Vetter <simona.vetter@ffwll.ch>
> > > > Cc: Dave Airlie <airlied@gmail.com>
> > > > Cc: Alistair Popple <apopple@nvidia.com>
> > > > Cc: <dri-devel@lists.freedesktop.org>
> > > > Cc: <linux-mm@kvack.org>
> > > > Cc: <linux-kernel@vger.kernel.org>
> > > > 
> > > > Assisted-by: GitHub Copilot:claude-sonnet-4.6 # Documentation
> > > > only.
> > > > Signed-off-by: Thomas Hellström
> > > > <thomas.hellstrom@linux.intel.com>
> > > > ---
> > > 
> > > LGTM, thanks!
> > > 
> > > Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> > 
> > Thanks, David.
> > 
> > Ack to merge this through drm together with the drm/xe patches?
> 
> Works for me, let me CC Andrew for awareness.
> 
> > 
> > If so, do I need an additional R-B in addition to any drm/xe
> > reviewers?
> 
> Not from MM people :)