[PATCH v4 02/33] mm/migrate: Add migrate_device_pfns

[Alistair Popple]

On Wed, Jan 29, 2025 at 11:51:41AM -0800, Matthew Brost wrote:
> Add migrate_device_pfns which prepares an array of pre-populated device
> pages for migration. This is needed for eviction of known set of
> non-contiguous devices pages to cpu pages which is a common case for SVM
> in DRM drivers using TTM.
> 
> v2:
>  - s/migrate_device_vma_range/migrate_device_prepopulated_range
>  - Drop extra mmu invalidation (Vetter)
> v3:
>  - s/migrate_device_prepopulated_range/migrate_device_pfns (Alistar)
>  - Use helper to lock device pages (Alistar)
>  - Update commit message with why this is required (Alistar)

Thanks! Looks good to me now so:

Reviewed-by: Alistair Popple <apopple at nvidia.com>

> Cc: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> ---
>  include/linux/migrate.h |  1 +
>  mm/migrate_device.c     | 52 +++++++++++++++++++++++++++++------------
>  2 files changed, 38 insertions(+), 15 deletions(-)
> 
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 002e49b2ebd9..6254746648cc 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -229,6 +229,7 @@ void migrate_vma_pages(struct migrate_vma *migrate);
>  void migrate_vma_finalize(struct migrate_vma *migrate);
>  int migrate_device_range(unsigned long *src_pfns, unsigned long start,
>  			unsigned long npages);
> +int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages);
>  void migrate_device_pages(unsigned long *src_pfns, unsigned long *dst_pfns,
>  			unsigned long npages);
>  void migrate_device_finalize(unsigned long *src_pfns,
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index 9cf26592ac93..19960743f927 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -876,6 +876,22 @@ void migrate_vma_finalize(struct migrate_vma *migrate)
>  }
>  EXPORT_SYMBOL(migrate_vma_finalize);
>  
> +static unsigned long migrate_device_pfn_lock(unsigned long pfn)
> +{
> +	struct folio *folio;
> +
> +	folio = folio_get_nontail_page(pfn_to_page(pfn));
> +	if (!folio)
> +		return 0;
> +
> +	if (!folio_trylock(folio)) {
> +		folio_put(folio);
> +		return 0;
> +	}
> +
> +	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> +}
> +
>  /**
>   * migrate_device_range() - migrate device private pfns to normal memory.
>   * @src_pfns: array large enough to hold migrating source device private pfns.
> @@ -900,29 +916,35 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start,
>  {
>  	unsigned long i, pfn;
>  
> -	for (pfn = start, i = 0; i < npages; pfn++, i++) {
> -		struct folio *folio;
> +	for (pfn = start, i = 0; i < npages; pfn++, i++)
> +		src_pfns[i] = migrate_device_pfn_lock(pfn);
>  
> -		folio = folio_get_nontail_page(pfn_to_page(pfn));
> -		if (!folio) {
> -			src_pfns[i] = 0;
> -			continue;
> -		}
> +	migrate_device_unmap(src_pfns, npages, NULL);
>  
> -		if (!folio_trylock(folio)) {
> -			src_pfns[i] = 0;
> -			folio_put(folio);
> -			continue;
> -		}
> +	return 0;
> +}
> +EXPORT_SYMBOL(migrate_device_range);
>  
> -		src_pfns[i] = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> -	}
> +/**
> + * migrate_device_pfns() - migrate device private pfns to normal memory.
> + * @src_pfns: pre-popluated array of source device private pfns to migrate.
> + * @npages: number of pages to migrate.
> + *
> + * Similar to migrate_device_range() but supports non-contiguous pre-popluated
> + * array of device pages to migrate.
> + */
> +int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages)
> +{
> +	unsigned long i;
> +
> +	for (i = 0; i < npages; i++)
> +		src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]);
>  
>  	migrate_device_unmap(src_pfns, npages, NULL);
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL(migrate_device_range);
> +EXPORT_SYMBOL(migrate_device_pfns);
>  
>  /*
>   * Migrate a device coherent folio back to normal memory. The caller should have
> -- 
> 2.34.1
>