Re: [PATCH 3/5] mm/notifier: add migration invalidation type

Jason Gunthorpe
2020-07-10T19:46:55Z

On Mon, Jul 06, 2020 at 03:23:45PM -0700, Ralph Campbell wrote:
> Currently migrate_vma_setup() calls mmu_notifier_invalidate_range_start()
> which flushes all device private page mappings whether or not a page
> is being migrated to/from device private memory. In order to not disrupt
> device mappings that are not being migrated, shift the responsibility
> for clearing device private mappings to the device driver and leave
> CPU page table unmapping handled by migrate_vma_setup(). To support
> this, the caller of migrate_vma_setup() should always set struct
> migrate_vma::src_owner to a non NULL value that matches the device
> private page->pgmap->owner. This value is then passed to the struct
> mmu_notifier_range with a new event type which the driver's invalidation
> function can use to avoid device MMU invalidations.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> include/linux/mmu_notifier.h | 7 +++++++
> mm/migrate.c | 8 +++++++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
> index fc68f3570e19..bd0b34dbe4de 100644
> +++ b/include/linux/mmu_notifier.h
> @@ -38,6 +38,10 @@ struct mmu_interval_notifier;
> *
> * @MMU_NOTIFY_RELEASE: used during mmu_interval_notifier invalidate to signal
> * that the mm refcount is zero and the range is no longer accessible.
> + *
> + * @MMU_NOTIFY_MIGRATE: used during migrate_vma_collect() invalidate to signal
> + * a device driver to possibly ignore the invalidation if the src_own
> + * field matches.
> */
> enum mmu_notifier_event {
> MMU_NOTIFY_UNMAP = 0,
> @@ -46,6 +50,7 @@ enum mmu_notifier_event {
> MMU_NOTIFY_PROTECTION_PAGE,
> MMU_NOTIFY_SOFT_DIRTY,
> MMU_NOTIFY_RELEASE,
> + MMU_NOTIFY_MIGRATE,
> };
>
> #define MMU_NOTIFIER_RANGE_BLOCKABLE (1 << 0)
> @@ -264,6 +269,7 @@ struct mmu_notifier_range {
> unsigned long end;
> unsigned flags;
> enum mmu_notifier_event event;
> + void *data;
> };

This generic member usually ends up a bit ugly, can we do a tagged
union instead?

union
{
void *migrate_pgmap_owner;
};

and probably drop the union until we actually need two things here.

Jason