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

[Ralph Campbell]

On 7/10/20 12:39 PM, Jason Gunthorpe wrote:
> 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@xxxxxxxxxx>
> >   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

OK, I'll send a v2 with this change.