[PATCH rfc 4/9] mm: remove MIGRATE_SYNC_NO_COPY mode

[Kefeng Wang <wangkefeng.wang@huawei.com>]

Commit 2916ecc0f9d4 ("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.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 fs/aio.c                     | 12 +-----------
 fs/hugetlbfs/inode.c         |  5 +----
 include/linux/migrate_mode.h |  5 -----
 mm/balloon_compaction.c      |  8 --------
 mm/migrate.c                 |  8 +-------
 mm/zsmalloc.c                |  8 --------
 6 files changed, 3 insertions(+), 43 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index bb2ff48991f3..1d0ca2a2776d 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -409,17 +409,7 @@ static int aio_migrate_folio(struct address_space *mapping, struct folio *dst,
 	struct kioctx *ctx;
 	unsigned long flags;
 	pgoff_t idx;
-	int rc;
-
-	/*
-	 * 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;
+	int rc = 0;
 
 	/* mapping->i_private_lock here protects against the kioctx teardown.  */
 	spin_lock(&mapping->i_private_lock);
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index ee13c2ca8ad2..52839ffdd9a1 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1129,10 +1129,7 @@ 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);
+	folio_migrate_copy(dst, src);
 
 	return MIGRATEPAGE_SUCCESS;
 }
diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
index f37cc03f9369..9fb482bb7323 100644
--- a/include/linux/migrate_mode.h
+++ b/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 {
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 22c96fed70b5..6597ebea8ae2 100644
--- a/mm/balloon_compaction.c
+++ b/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);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index a51ceebbe3b1..107965bbc852 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -668,10 +668,7 @@ 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);
+	folio_migrate_copy(dst, src);
 
 	return MIGRATEPAGE_SUCCESS;
 }
@@ -901,7 +898,6 @@ 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;
@@ -1159,7 +1155,6 @@ 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;
@@ -1370,7 +1365,6 @@ 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;
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index c937635e0ad1..b9ffe1a041ca 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1811,14 +1811,6 @@ 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 */
-- 
2.27.0