Re: [RFC 04/11] mm/migrate_device: THP migration of zone device pages

["Mika Penttilä" <mpenttil@redhat.com>]

Hi,

On 3/6/25 06:42, Balbir Singh wrote:
...

>  
>  			/*
>  			 * The only time there is no vma is when called from
> @@ -728,15 +1000,47 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>  					migrate->pgmap_owner);
>  				mmu_notifier_invalidate_range_start(&range);
>  			}
> -			migrate_vma_insert_page(migrate, addr, newpage,
> +
> +			if ((src_pfns[i] & MIGRATE_PFN_COMPOUND) &&
> +				(!(dst_pfns[i] & MIGRATE_PFN_COMPOUND))) {
> +				nr = HPAGE_PMD_NR;
> +				src_pfns[i] &= ~MIGRATE_PFN_COMPOUND;
> +				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
> +				goto next;
> +			}
> +
> +			migrate_vma_insert_page(migrate, addr, &dst_pfns[i],
>  						&src_pfns[i]);
> -			continue;
> +			goto next;
>  		}
>  
>  		newfolio = page_folio(newpage);
>  		folio = page_folio(page);
>  		mapping = folio_mapping(folio);
>  
> +		/*
> +		 * If THP migration is enabled, check if both src and dst
> +		 * can migrate large pages
> +		 */
> +		if (thp_migration_supported()) {
> +			if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) &&
> +				(src_pfns[i] & MIGRATE_PFN_COMPOUND) &&
> +				!(dst_pfns[i] & MIGRATE_PFN_COMPOUND)) {
> +
> +				if (!migrate) {
> +					src_pfns[i] &= ~(MIGRATE_PFN_MIGRATE |
> +							 MIGRATE_PFN_COMPOUND);
> +					goto next;
> +				}
> +				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;

This looks strange as is but patch 08 changes this to split and then
migrate.


> +			} else if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) &&
> +				(dst_pfns[i] & MIGRATE_PFN_COMPOUND) &&
> +				!(src_pfns[i] & MIGRATE_PFN_COMPOUND)) {
> +				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;

Should there be goto next; or similar here also, we are not migrating
this src?


> +			}
> +		}
> +
> +
>  		if (folio_is_device_private(newfolio) ||
>  		    folio_is_device_coherent(newfolio)) {
>  			if (mapping) {
> @@ -749,7 +1053,7 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>  				if (!folio_test_anon(folio) ||
>  				    !folio_free_swap(folio)) {
>  					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
> -					continue;
> +					goto next;
>  				}
>  			}
>  		} else if (folio_is_zone_device(newfolio)) {
> @@ -757,7 +1061,7 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>  			 * Other types of ZONE_DEVICE page are not supported.
>  			 */
>  			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
> -			continue;
> +			goto next;
>  		}
>  
>  		BUG_ON(folio_test_writeback(folio));
> @@ -769,6 +1073,8 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>  			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>  		else
>  			folio_migrate_flags(newfolio, folio);
> +next:
> +		i += nr;
>  	}
>  
>  	if (notified)
> @@ -899,24 +1205,40 @@ EXPORT_SYMBOL(migrate_vma_finalize);
>  int migrate_device_range(unsigned long *src_pfns, unsigned long start,
>  			unsigned long npages)
>  {
> -	unsigned long i, pfn;
> +	unsigned long i, j, pfn;
>  
> -	for (pfn = start, i = 0; i < npages; pfn++, i++) {
> -		struct folio *folio;
> +	i = 0;
> +	pfn = start;
> +	while (i < npages) {
> +		struct page *page = pfn_to_page(pfn);
> +		struct folio *folio = page_folio(page);
> +		unsigned int nr = 1;
>  
>  		folio = folio_get_nontail_page(pfn_to_page(pfn));
>  		if (!folio) {
>  			src_pfns[i] = 0;
> -			continue;
> +			goto next;
>  		}
>  
>  		if (!folio_trylock(folio)) {
>  			src_pfns[i] = 0;
>  			folio_put(folio);
> -			continue;
> +			goto next;
>  		}
>  
>  		src_pfns[i] = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> +		nr = folio_nr_pages(folio);
> +		if (nr > 1) {
> +			src_pfns[i] |= MIGRATE_PFN_COMPOUND;
> +			for (j = 1; j < nr; j++)
> +				src_pfns[i+j] = 0;
> +			i += j;
> +			pfn += j;
> +			continue;
> +		}
> +next:
> +		i++;
> +		pfn++;
>  	}
>  
>  	migrate_device_unmap(src_pfns, npages, NULL);

--Mika