Nouveau - Jul 2020 - [PATCH 3/5] mm/notifier: add migration invalidation type

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 at 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

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