[PATCH 2/3] mm/swap: add a new swap_ops.h header to allow for pluggable swap ops

[Christoph Hellwig <hch@lst.de>]

Add a new header to declare the swap_iocb, swap_ops and swap_ctx to
allow for swap_ops implementations outside of mm/page_io.c.  This
will be used to remove the double indirection for file system-based
swap.

Note that there already is a swapops.h header, which is totally
unrelated to struct swap_ops.  The close naming is a bit unfortunate,
but I could not think of a better name for this header.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 MAINTAINERS              |  1 +
 include/linux/swap_ops.h | 39 +++++++++++++++++++++++++++++++++++++++
 mm/madvise.c             |  1 +
 mm/page_io.c             | 10 +---------
 mm/shmem.c               |  1 +
 mm/swap.h                | 23 +----------------------
 mm/swap_state.c          |  1 +
 mm/vmscan.c              |  1 +
 8 files changed, 46 insertions(+), 31 deletions(-)
 create mode 100644 include/linux/swap_ops.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 5da77924c6f0..cda42b7ed945 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17240,6 +17240,7 @@ S:	Maintained
 F:	Documentation/ABI/testing/sysfs-kernel-mm-swap
 F:	Documentation/mm/swap-table.rst
 F:	include/linux/swap.h
+F:	include/linux/swap_ops.h
 F:	include/linux/swapfile.h
 F:	include/linux/swapops.h
 F:	mm/page_io.c
diff --git a/include/linux/swap_ops.h b/include/linux/swap_ops.h
new file mode 100644
index 000000000000..e92b4f532604
--- /dev/null
+++ b/include/linux/swap_ops.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _MM_SWAP_OPS_H
+#define _MM_SWAP_OPS_H
+
+#include <linux/swap.h> /* for SWAP_CLUSTER_MAX */
+
+struct swap_iocb {
+	union {
+		struct kiocb	iocb;
+		struct bio	bio;
+	};
+	struct bio_vec		bvecs[SWAP_CLUSTER_MAX];
+	int			nr_bvecs;
+	int			len;
+};
+
+struct swap_io_ctx {
+	struct swap_iocb	*sio;
+	struct swap_info_struct	*sis;
+};
+
+/*
+ * SWAP_OPS_F_REQUIRE_NOFS:
+ *	When set, all reclaim operations must operated as GFS_NOFS and not
+ *	just GFP_NOIO, as GFP_NOIO allocations could recourse into the
+ *	file system backing this swap file.
+ */
+#define SWAP_OPS_F_REQUIRE_NOFS		(1U << 0)
+
+struct swap_ops {
+	unsigned int		flags;
+
+	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);
+};
+
+#endif /* _MM_SWAP_OPS_H */
diff --git a/mm/madvise.c b/mm/madvise.c
index 07a21ca31bad..c179938097bf 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -32,6 +32,7 @@
 #include <linux/leafops.h>
 #include <linux/shmem_fs.h>
 #include <linux/mmu_notifier.h>
+#include <linux/swap_ops.h>
 
 #include <asm/tlb.h>
 
diff --git a/mm/page_io.c b/mm/page_io.c
index c984a4023a65..e741e67d6592 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -25,6 +25,7 @@
 #include <linux/sched/task.h>
 #include <linux/delayacct.h>
 #include <linux/zswap.h>
+#include <linux/swap_ops.h>
 #include "swap.h"
 #include "swap_table.h"
 
@@ -300,15 +301,6 @@ static bool folio_blkg_can_merge(struct folio *folio, struct folio *prev_folio)
 #define bio_associate_blkg_from_page(bio, folio)		do { } while (0)
 #endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
 
-struct swap_iocb {
-	union {
-		struct kiocb	iocb;
-		struct bio	bio;
-	};
-	struct bio_vec		bvecs[SWAP_CLUSTER_MAX];
-	int			nr_bvecs;
-	int			len;
-};
 static mempool_t *sio_pool;
 
 int sio_pool_init(void)
diff --git a/mm/shmem.c b/mm/shmem.c
index 5071177059a9..797c42f024a0 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -41,6 +41,7 @@
 #include <linux/swapfile.h>
 #include <linux/iversion.h>
 #include <linux/unicode.h>
+#include <linux/swap_ops.h>
 #include "swap.h"
 
 static struct vfsmount *shm_mnt __ro_after_init;
diff --git a/mm/swap.h b/mm/swap.h
index abd26588abd2..19ea61c97df2 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -8,6 +8,7 @@
 struct mempolicy;
 struct swap_iocb;
 struct swap_memcg_table;
+struct swap_io_ctx;
 
 #if defined(MAX_POSSIBLE_PHYSMEM_BITS)
 #define SWAP_CACHE_PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
@@ -77,28 +78,6 @@ enum swap_cluster_flags {
 	CLUSTER_FLAG_MAX,
 };
 
-struct swap_io_ctx {
-	struct swap_iocb	*sio;
-	struct swap_info_struct	*sis;
-};
-
-/*
- * SWAP_OPS_F_REQUIRE_NOFS:
- *	When set, all reclaim operations must operated as GFS_NOFS and not
- *	just GFP_NOIO, as GFP_NOIO allocations could recourse into the
- *	file system backing this swap file.
- */
-#define SWAP_OPS_F_REQUIRE_NOFS		(1U << 0)
-
-struct swap_ops {
-	unsigned int		flags;
-
-	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 */
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 5be825911e64..b76eb3d876fd 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -23,6 +23,7 @@
 #include <linux/huge_mm.h>
 #include <linux/shmem_fs.h>
 #include <linux/sysctl.h>
+#include <linux/swap_ops.h>
 #include "internal.h"
 #include "swap_table.h"
 #include "swap.h"
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e26c6931f5fd..a12eb79c89c5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -58,6 +58,7 @@
 #include <linux/random.h>
 #include <linux/mmu_notifier.h>
 #include <linux/parser.h>
+#include <linux/swap_ops.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
-- 
2.53.0