mm: remove the unused MIGRATE_PFN_DEVICE flag

No one ever checks this flag, and we could easily get that information
from the page if needed.

Link: https://lore.kernel.org/r/20190814075928.23766-10-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -580,8 +580,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
 			*dma_addr))
 		goto out_dma_unmap;
 
-	return migrate_pfn(page_to_pfn(dpage)) |
-		MIGRATE_PFN_LOCKED | MIGRATE_PFN_DEVICE;
+	return migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
 
 out_dma_unmap:
 	dma_unmap_page(dev, *dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);

include/linux/migrate.h

@@ -166,7 +166,6 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 #define MIGRATE_PFN_MIGRATE	(1UL << 1)
 #define MIGRATE_PFN_LOCKED	(1UL << 2)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
-#define MIGRATE_PFN_DEVICE	(1UL << 4)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)

mm/migrate.c

@@ -2237,8 +2237,8 @@ again:
 				goto next;
 
 			page = device_private_entry_to_page(entry);
-			mpfn = migrate_pfn(page_to_pfn(page))|
-				MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
+			mpfn = migrate_pfn(page_to_pfn(page)) |
+					MIGRATE_PFN_MIGRATE;
 			if (is_write_device_private_entry(entry))
 				mpfn |= MIGRATE_PFN_WRITE;
 		} else {