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

["Zhaoyu Liu" <liuzhaoyu.zackary@picoheart.com>]

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@picoheart.com>
---
 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