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

[David Hildenbrand (Arm)]

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@xxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Simona Vetter <simona.vetter@xxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxx>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
> Cc: <linux-mm@xxxxxxxxx>
> Cc: <linux-kernel@xxxxxxxxxxxxxxx>
> 
> Assisted-by: GitHub Copilot:claude-sonnet-4.6 # Documentation only.
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---

LGTM, thanks!

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David