Re: [PATCH v2] drm/pagemap: no need to recheck own pagemap in migrate_to_devmem

[Zhaoyu Liu]

Hi,
Could you please help review this patch?

Thanks,
zackary

On Thu, Aug 06, 2026 at 09:21:41PM +0800, Zhaoyu Liu wrote:
> The second loop in drm_pagemap_migrate_to_devmem() checks
> `page_pgmap(src_page) == pagemap && !can_migrate_same_pagemap` to skip
> pages already on the target pagemap. However, this condition is always
> false at this point: if can_migrate_same_pagemap is false and any own
> pages exist, the first loop already returns -EBUSY before reaching here.
> 
> v2:
>   - Skip the no-op migrate_vma_pages() when all pages already reside on
>     the target pagemap.
> 
> Signed-off-by: Zhaoyu Liu <liuzhaoyu.zackary@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_pagemap.c | 21 ++++++---------------
>  1 file changed, 6 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 15c78eca180b..64922b944092 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -698,7 +698,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  		 * nothing. Raced or unknown device pages.
>  		 */
>  		err = -EBUSY;
> -		goto err_aborted_migration;
> +		goto direct_finalize;
>  	}
>  
>  	/* Count device-private pages to migrate */
> @@ -719,19 +719,17 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  	if (own_pages == npages) {
>  		err = 0;
>  		drm_dbg(dpagemap->drm, "Migration wasn't necessary.\n");
> -		goto err_aborted_migration;
> +		goto direct_finalize;
>  	} else if (own_pages && !mdetails->can_migrate_same_pagemap) {
>  		err = -EBUSY;
>  		drm_dbg(dpagemap->drm, "Migration aborted due to fragmentation.\n");
> -		goto err_aborted_migration;
> +		goto direct_finalize;
>  	}
>  
>  	err = ops->populate_devmem_pfn(devmem_allocation, npages, migrate.dst);
>  	if (err)
>  		goto err_aborted_migration;
>  
> -	own_pages = 0;
> -
>  	for (i = 0; i < npages;) {
>  		unsigned long j;
>  		struct page *page = pfn_to_page(migrate.dst[i]);
> @@ -744,12 +742,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  			struct drm_pagemap_zdd *src_zdd =
>  				drm_pagemap_page_zone_device_data(src_page);
>  
> -			if (page_pgmap(src_page) == pagemap &&
> -			    !mdetails->can_migrate_same_pagemap) {
> -				migrate.dst[i] = 0;
> -				own_pages++;
> -				goto next;
> -			}
> +			/* Own or peer device private page */
>  			cur.dpagemap = src_zdd->dpagemap;
>  			cur.ops = src_zdd->devmem_allocation->ops;
>  			cur.device = cur.dpagemap->drm->dev;
> @@ -786,7 +779,6 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  			goto err_finalize;
>  		}
>  
> -next:
>  		i += NR_PAGES(order);
>  	}
>  
> @@ -797,8 +789,6 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  	if (err)
>  		goto err_finalize;
>  
> -	drm_WARN_ON(dpagemap->drm, !!own_pages);
> -
>  	dma_fence_put(devmem_allocation->pre_migrate_fence);
>  	devmem_allocation->pre_migrate_fence = NULL;
>  
> @@ -822,11 +812,12 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  		i += nr_pages;
>  	}
>  
> -	if (!err && migrated_pages < npages - own_pages) {
> +	if (!err && migrated_pages < npages) {
>  		drm_dbg(dpagemap->drm, "Raced while finalizing migration.\n");
>  		err = -EBUSY;
>  	}
>  
> +direct_finalize:
>  	migrate_vma_finalize(&migrate);
>  err_free:
>  	drm_pagemap_zdd_put(zdd);
> -- 
> 2.34.1