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

Ralph Campbell
2020-07-10T20:17:54Z

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@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.