[PATCH 5/7] mm/swap: use swap_ops to register swap device's methods

[Christoph Hellwig <hch@lst.de>]

This simplifies codes and makes logic clearer. And also makes later any
new swap device type being added easier to handle.

Currently there are two types of swap devices: fs and bdev.

Suggested-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Baoquan He <baoquan.he@linux.dev>
[hch: updated for the new submit and can_merge abstraction]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/swap.h |  1 +
 mm/page_io.c         | 68 ++++++++++++++++++++++++++++----------------
 mm/swap.h            | 10 +++++++
 mm/swapfile.c        |  4 +++
 4 files changed, 58 insertions(+), 25 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8f0f68e245ba..74ceb7a88fd5 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -282,6 +282,7 @@ struct swap_info_struct {
 	struct work_struct reclaim_work; /* reclaim worker */
 	struct list_head discard_clusters; /* discard clusters list */
 	struct plist_node avail_list;   /* entry in swap_avail_head */
+	const struct swap_ops *ops;
 };
 
 static inline swp_entry_t page_swap_entry(struct page *page)
diff --git a/mm/page_io.c b/mm/page_io.c
index 6009f6991b73..d2b11db1a57f 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -333,21 +333,7 @@ static bool swap_can_merge(struct swap_io_ctx *ctx, struct folio *folio,
 
 	if (ctx->sis != sis)
 		return false;
-
-	if (sis->flags & SWP_FS_OPS) {
-		if (swap_dev_pos(folio->swap) !=
-		    swap_dev_pos(prev_folio->swap) + prev_folio_size)
-			return false;
-	} else {
-		if (swap_folio_sector(folio) !=
-		    swap_folio_sector(prev_folio) +
-		    (prev_folio_size >> SECTOR_SHIFT))
-			return false;
-		if (rw == WRITE && !folio_blkg_can_merge(folio, prev_folio))
-			return false;
-	}
-
-	return true;
+	return sis->ops->can_merge(folio, prev_folio, prev_folio_size, rw);
 }
 
 static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
@@ -645,6 +631,23 @@ static void swap_bdev_submit_read(struct swap_io_ctx *ctx)
 	}
 }
 
+static bool swap_bdev_can_merge(struct folio *folio, struct folio *prev_folio,
+		size_t prev_folio_size, int rw)
+{
+	if (swap_folio_sector(folio) !=
+	    swap_folio_sector(prev_folio) + (prev_folio_size >> SECTOR_SHIFT))
+		return false;
+	if (rw == WRITE && !folio_blkg_can_merge(folio, prev_folio))
+		return false;
+	return true;
+}
+
+const struct swap_ops swap_bdev_ops = {
+	.submit_write		= swap_bdev_submit_write,
+	.submit_read		= swap_bdev_submit_read,
+	.can_merge		= swap_bdev_can_merge,
+};
+
 static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
 {
 	struct swap_iocb *sio = ctx->sio;
@@ -665,15 +668,34 @@ static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
 		sio->iocb.ki_complete(&sio->iocb, ret);
 }
 
+static void swap_fs_submit_write(struct swap_io_ctx *ctx)
+{
+	swap_fs_submit(ctx, WRITE);
+}
+
+static void swap_fs_submit_read(struct swap_io_ctx *ctx)
+{
+	swap_fs_submit(ctx, READ);
+}
+
+static bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio,
+		size_t prev_folio_size, int rw)
+{
+	return swap_dev_pos(folio->swap) ==
+		swap_dev_pos(prev_folio->swap) + prev_folio_size;
+}
+
+const struct swap_ops swap_fs_ops = {
+	.submit_write		= swap_fs_submit_write,
+	.submit_read		= swap_fs_submit_read,
+	.can_merge		= swap_fs_can_merge,
+};
+
 void swap_write_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
-
-	if (ctx->sis->flags & SWP_FS_OPS)
-		swap_fs_submit(ctx, WRITE);
-	else
-		swap_bdev_submit_write(ctx);
+	ctx->sis->ops->submit_write(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
 }
@@ -682,11 +704,7 @@ void swap_read_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
-
-	if (ctx->sis->flags & SWP_FS_OPS)
-		swap_fs_submit(ctx, READ);
-	else
-		swap_bdev_submit_read(ctx);
+	ctx->sis->ops->submit_read(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
 }
diff --git a/mm/swap.h b/mm/swap.h
index b6ba80c2afb0..5119feff0e93 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -84,6 +84,13 @@ struct swap_io_ctx {
 	struct swap_info_struct	*sis;
 };
 
+struct swap_ops {
+	bool (*can_merge)(struct folio *folio, struct folio *prev_folio,
+			size_t prev_folio_size, int rw);
+	void (*submit_write)(struct swap_io_ctx *ctx);
+	void (*submit_read)(struct swap_io_ctx *ctx);
+};
+
 #ifdef CONFIG_SWAP
 #include <linux/swapops.h> /* for swp_offset */
 #include <linux/blk_types.h> /* for bio_end_io_t */
@@ -471,6 +478,9 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 
 #endif /* CONFIG_SWAP */
 
+extern const struct swap_ops swap_bdev_ops;
+extern const struct swap_ops swap_fs_ops;
+
 int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		struct list_head *folio_list);
 
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1887df22bd1e..b291510813a6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2945,6 +2945,8 @@ static int setup_swap_extents(struct swap_info_struct *sis,
 	if (ret)
 		return ret;
 
+	sis->ops = &swap_bdev_ops;
+
 	if (S_ISBLK(inode->i_mode)) {
 		ret = add_swap_extent(sis, 0, sis->max, 0);
 		*span = sis->pages;
@@ -2955,6 +2957,8 @@ static int setup_swap_extents(struct swap_info_struct *sis,
 		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
 		if (ret < 0)
 			return ret;
+		if (sis->flags & SWP_FS_OPS)
+			sis->ops = &swap_fs_ops;
 		sis->flags |= SWP_ACTIVATED;
 		return ret;
 	}
-- 
2.53.0