mm: remove MIGRATE_SYNC_NO_COPY mode

Commit 2916ecc0f9 ("mm/migrate: new migrate mode MIGRATE_SYNC_NO_COPY")
introduce a new MIGRATE_SYNC_NO_COPY mode to allow to offload the copy to
a device DMA engine, which is only used __migrate_device_pages() to decide
whether or not copy the old page, and the MIGRATE_SYNC_NO_COPY mode only
set in hmm, as the MIGRATE_SYNC_NO_COPY set is removed by previous
cleanup, it seems that we could remove the unnecessary
MIGRATE_SYNC_NO_COPY.

Link: https://lkml.kernel.org/r/20240524052843.182275-6-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/aio.c

@@ -410,17 +410,7 @@ static int aio_migrate_folio(struct address_space *mapping, struct folio *dst,
 	struct kioctx *ctx;
 	unsigned long flags;
 	pgoff_t idx;
-	int rc;
+	int rc = 0;
-
-	/*
-	 * We cannot support the _NO_COPY case here, because copy needs to
-	 * happen under the ctx->completion_lock. That does not work with the
-	 * migration workflow of MIGRATE_SYNC_NO_COPY.
-	 */
-	if (mode == MIGRATE_SYNC_NO_COPY)
-		return -EINVAL;
-
-	rc = 0;
 
 	/* mapping->i_private_lock here protects against the kioctx teardown.  */
 	spin_lock(&mapping->i_private_lock);

fs/hugetlbfs/inode.c

@@ -1128,10 +1128,7 @@ static int hugetlbfs_migrate_folio(struct address_space *mapping,
 		hugetlb_set_folio_subpool(src, NULL);
 	}
 
-	if (mode != MIGRATE_SYNC_NO_COPY)
 	folio_migrate_copy(dst, src);
-	else
-		folio_migrate_flags(dst, src);
 
 	return MIGRATEPAGE_SUCCESS;
 }

include/linux/migrate_mode.h

@@ -7,16 +7,11 @@
  *	on most operations but not ->writepage as the potential stall time
  *	is too significant
  * MIGRATE_SYNC will block when migrating pages
- * MIGRATE_SYNC_NO_COPY will block when migrating pages but will not copy pages
- *	with the CPU. Instead, page copy happens outside the migratepage()
- *	callback and is likely using a DMA engine. See migrate_vma() and HMM
- *	(mm/hmm.c) for users of this mode.
  */
 enum migrate_mode {
 	MIGRATE_ASYNC,
 	MIGRATE_SYNC_LIGHT,
 	MIGRATE_SYNC,
-	MIGRATE_SYNC_NO_COPY,
 };
 
 enum migrate_reason {

mm/balloon_compaction.c

@@ -234,14 +234,6 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,
 {
 	struct balloon_dev_info *balloon = balloon_page_device(page);
 
-	/*
-	 * We can not easily support the no copy case here so ignore it as it
-	 * is unlikely to be used with balloon pages. See include/linux/hmm.h
-	 * for a user of the MIGRATE_SYNC_NO_COPY mode.
-	 */
-	if (mode == MIGRATE_SYNC_NO_COPY)
-		return -EINVAL;
-
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 

mm/migrate.c

@@ -671,10 +671,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 	if (src_private)
 		folio_attach_private(dst, folio_detach_private(src));
 
-	if (mode != MIGRATE_SYNC_NO_COPY)
 	folio_migrate_copy(dst, src);
-	else
-		folio_migrate_flags(dst, src);
 	return MIGRATEPAGE_SUCCESS;
 }
 
@@ -903,7 +900,6 @@ static int fallback_migrate_folio(struct address_space *mapping,
 		/* Only writeback folios in full synchronous migration */
 		switch (mode) {
 		case MIGRATE_SYNC:
-		case MIGRATE_SYNC_NO_COPY:
 			break;
 		default:
 			return -EBUSY;
@@ -1161,7 +1157,6 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 		 */
 		switch (mode) {
 		case MIGRATE_SYNC:
-		case MIGRATE_SYNC_NO_COPY:
 			break;
 		default:
 			rc = -EBUSY;
@@ -1372,7 +1367,6 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio,
 			goto out;
 		switch (mode) {
 		case MIGRATE_SYNC:
-		case MIGRATE_SYNC_NO_COPY:
 			break;
 		default:
 			goto out;

mm/zsmalloc.c

@@ -1752,14 +1752,6 @@ static int zs_page_migrate(struct page *newpage, struct page *page,
 	unsigned long old_obj, new_obj;
 	unsigned int obj_idx;
 
-	/*
-	 * We cannot support the _NO_COPY case here, because copy needs to
-	 * happen under the zs lock, which does not work with
-	 * MIGRATE_SYNC_NO_COPY workflow.
-	 */
-	if (mode == MIGRATE_SYNC_NO_COPY)
-		return -EINVAL;
-
 	VM_BUG_ON_PAGE(!PageIsolated(page), page);
 
 	/* The page is locked, so this pointer must remain valid */