swap_ops updates

swap_ops updates

[Christoph Hellwig]

Hi all,

this series is a follow on to the swap ops series now in mm-unstable.

The first patch reintroduces direct folio writes for synchronous
swap files, the other two remove the double indirect for file
system based swap.

[PATCH 1/3] mm/swap: revert to single-folio writes for synchronous swap devices

[Christoph Hellwig]

Kairui Song reported that zram benefits from submitting each folio
directly instead of batching up I/O because the classic LRU scanning
benefits from clearing the folio writeback bit in the scan loop.

Accommodate that by kicking off reads for synchronous devices for
each iteration.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/page_io.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index e4fa7ffffe8b..c984a4023a65 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -358,7 +358,16 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
 	}
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+
+	/*
+	 * Write out the iocb if we filled it, or if the device is synchronous.
+	 *
+	 * The latter is to work around expectations in the classic LRU code
+	 * which make synchronous clearing of the folio writeback flag in the
+	 * reclaim path beneficial.
+	 */
+	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
+	    (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
 		if (rw == WRITE)
 			swap_write_submit(ctx);
 		else
-- 
2.53.0

Re: [PATCH 1/3] mm/swap: revert to single-folio writes for synchronous swap devices

[Usama Arif]

On Wed, 22 Jul 2026 15:06:07 +0200 Christoph Hellwig <hch@lst.de> wrote:

> Kairui Song reported that zram benefits from submitting each folio
> directly instead of batching up I/O because the classic LRU scanning
> benefits from clearing the folio writeback bit in the scan loop.
> 
> Accommodate that by kicking off reads for synchronous devices for

s/reads/writes/ ?

> each iteration.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  mm/page_io.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 


Change makes sense.

After the commit message fix above, feel free to add

Acked-by: Usama Arif <usama.arif@linux.dev>


> diff --git a/mm/page_io.c b/mm/page_io.c
> index e4fa7ffffe8b..c984a4023a65 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -358,7 +358,16 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
>  	}
>  	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
>  	sio->len += folio_size(folio);
> -	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
> +
> +	/*
> +	 * Write out the iocb if we filled it, or if the device is synchronous.
> +	 *
> +	 * The latter is to work around expectations in the classic LRU code
> +	 * which make synchronous clearing of the folio writeback flag in the
> +	 * reclaim path beneficial.
> +	 */
> +	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
> +	    (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
>  		if (rw == WRITE)
>  			swap_write_submit(ctx);
>  		else
> -- 
> 2.53.0
> 
> 

Re: [PATCH 1/3] mm/swap: revert to single-folio writes for synchronous swap devices

[Christoph Hellwig]

On Wed, Jul 22, 2026 at 09:36:00AM -0700, Usama Arif wrote:
> On Wed, 22 Jul 2026 15:06:07 +0200 Christoph Hellwig <hch@lst.de> wrote:
> 
> > Kairui Song reported that zram benefits from submitting each folio
> > directly instead of batching up I/O because the classic LRU scanning
> > benefits from clearing the folio writeback bit in the scan loop.
> > 
> > Accommodate that by kicking off reads for synchronous devices for
> 
> s/reads/writes/ ?

Yes, fixed.

Re: [PATCH 1/3] mm/swap: revert to single-folio writes for synchronous swap devices

[Chris Li]

On Wed, Jul 22, 2026 at 6:06 AM Christoph Hellwig <hch@lst.de> wrote:
>
> Kairui Song reported that zram benefits from submitting each folio
> directly instead of batching up I/O because the classic LRU scanning
> benefits from clearing the folio writeback bit in the scan loop.
>
> Accommodate that by kicking off reads for synchronous devices for
> each iteration.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Chris Li <chrisl@kernel.org>

Chris

> ---
>  mm/page_io.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_io.c b/mm/page_io.c
> index e4fa7ffffe8b..c984a4023a65 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -358,7 +358,16 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
>         }
>         bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
>         sio->len += folio_size(folio);
> -       if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
> +
> +       /*
> +        * Write out the iocb if we filled it, or if the device is synchronous.
> +        *
> +        * The latter is to work around expectations in the classic LRU code
> +        * which make synchronous clearing of the folio writeback flag in the
> +        * reclaim path beneficial.
> +        */
> +       if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
> +           (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
>                 if (rw == WRITE)
>                         swap_write_submit(ctx);
>                 else
> --
> 2.53.0
>

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

[Christoph Hellwig]

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

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

[Usama Arif]

On Wed, 22 Jul 2026 15:06:08 +0200 Christoph Hellwig <hch@lst.de> wrote:

> 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;
> +};

zswap uses this struct, I think you need to include the header in zswap.c
as well, good to check if the build is passing with CONFIG_ZSWAP=y

> +
> +/*
> + * 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
> 
> 

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

[Christoph Hellwig]

On Wed, Jul 22, 2026 at 09:32:17AM -0700, Usama Arif wrote:
> > +struct swap_io_ctx {
> > +	struct swap_iocb	*sio;
> > +	struct swap_info_struct	*sis;
> > +};
> 
> zswap uses this struct, I think you need to include the header in zswap.c
> as well, good to check if the build is passing with CONFIG_ZSWAP=y

Yes.  The buildbot was nice enough to remind me of that just a little
after it gave an all ok...

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

[Chris Li]

On Wed, Jul 22, 2026 at 6:06 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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.

Can you please clarify if this commit introduces any functional or API
level change this commit other than moving the code around?
I don't think so, but I just want some clarification. Maybe there is a
minor API change to remove the double indirection that I don't see.
Anyway, it would be better to spell it out in the commit message.

Chris

[PATCH 3/3] mm/swap: move swap_ops into file systems for file system-based swap

[Christoph Hellwig]

Currently swap to and from file systems goes through two indirect calls
between the swap ops and the swap_rw method.  Reduce this by directly
providing the swap_ops from the file system.

For this refactor swap_fs_submit into a swap_fs_prepare_rw helper that
initializes the iov_iter on the callers stack so that file systems can
call it directly, and use that to initialize file system specific ops
in NFS and the SMB client, which then get passed to swap_fs_activate.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/filesystems/locking.rst |  9 +---
 Documentation/filesystems/vfs.rst     |  8 +---
 fs/nfs/direct.c                       | 20 ---------
 fs/nfs/file.c                         | 42 ++++++++++++++++--
 fs/smb/client/file.c                  | 63 +++++++++++++++++----------
 include/linux/fs.h                    |  1 -
 include/linux/nfs_fs.h                |  1 -
 include/linux/swap.h                  |  6 ---
 include/linux/swap_ops.h              |  5 +++
 mm/page_io.c                          | 34 +++------------
 10 files changed, 93 insertions(+), 96 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 1a50d41a39a1..f58a8d7d5897 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -266,7 +266,6 @@ prototypes::
 	int (*error_remove_folio)(struct address_space *, struct folio *);
 	int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
 	int (*swap_deactivate)(struct file *);
-	int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
 
 locking rules:
 	All except dirty_folio and free_folio may block
@@ -291,7 +290,6 @@ is_partially_uptodate:	yes
 error_remove_folio:	yes
 swap_activate:		no
 swap_deactivate:	no
-swap_rw:		yes, unlocks
 ======================	======================== =========	===============
 
 ->write_begin(), ->write_end() and ->read_folio() may be called from
@@ -355,15 +353,12 @@ should perform any validation and preparation necessary to ensure that
 writes can be performed with minimal memory allocation.  It should call
 add_swap_extent(), or the helper iomap_swapfile_activate(), and return
 the number of extents added.  If IO should be submitted through
-->swap_rw(), it should call swap_fs_activate, otherwise IO will be submitted
-directly to the block device ``sis->bdev``.
+the file system it should call swap_fs_activate, otherwise IO will be
+submitted directly to the block device ``sis->bdev``.
 
 ->swap_deactivate() will be called in the sys_swapoff()
 path after ->swap_activate() returned success.
 
-->swap_rw will be called for swap IO if swap_fs_activate was called by
-->swap_activate().
-
 file_lock_operations
 ====================
 
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index e7677423a20f..c437a342d4f3 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -776,7 +776,6 @@ cache in your filesystem.  The following members are defined:
 		int (*error_remove_folio)(struct mapping *mapping, struct folio *);
 		int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
 		int (*swap_deactivate)(struct file *);
-		int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
 	};
 
 ``read_folio``
@@ -977,16 +976,13 @@ cache in your filesystem.  The following members are defined:
 	can be performed with minimal memory allocation.  It should call
 	add_swap_extent(), or the helper iomap_swapfile_activate(), and
 	return the number of extents added.  If IO should be submitted
-	through ->swap_rw(), it should call swap_fs_activate, otherwise IO will
-	be submitted directly to the block device ``sis->bdev``.
+	through the file system it should call swap_fs_activate, otherwise IO
+	will be submitted directly to the block device ``sis->bdev``.
 
 ``swap_deactivate``
 	Called during swapoff on files where swap_activate was
 	successful.
 
-``swap_rw``
-	Called to read or write swap pages when swap_fs_activate was called.
-
 The File Object
 ===============
 
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index e626c72495e6..ccafdc1ce64d 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -145,26 +145,6 @@ static void nfs_direct_file_adjust_size_locked(struct inode *inode,
 	}
 }
 
-/**
- * nfs_swap_rw - NFS address space operation for swap I/O
- * @iocb: target I/O control block
- * @iter: I/O buffer
- *
- * Perform IO to the swap-file.  This is much like direct IO.
- */
-int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
-{
-	ssize_t ret;
-
-	if (iov_iter_rw(iter) == READ)
-		ret = nfs_file_direct_read(iocb, iter, true);
-	else
-		ret = nfs_file_direct_write(iocb, iter, true);
-	if (ret < 0)
-		return ret;
-	return 0;
-}
-
 static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
 {
 	unsigned int i;
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 851d93a09988..e1bdd10b35f1 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -29,9 +29,8 @@
 #include <linux/pagemap.h>
 #include <linux/gfp.h>
 #include <linux/rmap.h>
-#include <linux/swap.h>
 #include <linux/compaction.h>
-
+#include <linux/swap_ops.h>
 #include <linux/uaccess.h>
 #include <linux/filelock.h>
 
@@ -575,6 +574,38 @@ static int nfs_launder_folio(struct folio *folio)
 	return ret;
 }
 
+#ifdef CONFIG_SWAP
+static void nfs_swap_submit_write(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct iov_iter iter;
+	int ret;
+
+	swap_fs_prepare_rw(ctx, WRITE, &iter);
+	ret = nfs_file_direct_write(&sio->iocb, &iter, true);
+	if (ret != -EIOCBQUEUED)
+		sio->iocb.ki_complete(&sio->iocb, ret);
+}
+
+static void nfs_swap_submit_read(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct iov_iter iter;
+	int ret;
+
+	swap_fs_prepare_rw(ctx, READ, &iter);
+	ret = nfs_file_direct_read(&sio->iocb, &iter, true);
+	if (ret != -EIOCBQUEUED)
+		sio->iocb.ki_complete(&sio->iocb, ret);
+}
+
+static const struct swap_ops nfs_swap_ops = {
+	.flags			= SWAP_OPS_F_REQUIRE_NOFS,
+	.submit_write		= nfs_swap_submit_write,
+	.submit_read		= nfs_swap_submit_read,
+	.can_merge		= swap_fs_can_merge,
+};
+
 static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 						sector_t *span)
 {
@@ -597,7 +628,7 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 	ret = rpc_clnt_swap_activate(clnt);
 	if (ret)
 		return ret;
-	ret = swap_fs_activate(sis);
+	ret = swap_fs_activate(sis, &nfs_swap_ops);
 	if (ret < 0) {
 		rpc_clnt_swap_deactivate(clnt);
 		return ret;
@@ -620,6 +651,10 @@ static void nfs_swap_deactivate(struct file *file)
 	if (cl->rpc_ops->disable_swap)
 		cl->rpc_ops->disable_swap(file_inode(file));
 }
+#else
+#define nfs_swap_activate	NULL
+#define nfs_swap_deactivate	NULL
+#endif /* CONFIG_SWAP */
 
 const struct address_space_operations nfs_file_aops = {
 	.read_folio = nfs_read_folio,
@@ -636,7 +671,6 @@ const struct address_space_operations nfs_file_aops = {
 	.error_remove_folio = generic_error_remove_folio,
 	.swap_activate = nfs_swap_activate,
 	.swap_deactivate = nfs_swap_deactivate,
-	.swap_rw = nfs_swap_rw,
 };
 
 /*
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 081bb16abeb4..190e24199fa1 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -20,7 +20,7 @@
 #include <linux/delay.h>
 #include <linux/mount.h>
 #include <linux/slab.h>
-#include <linux/swap.h>
+#include <linux/swap_ops.h>
 #include <linux/mm.h>
 #include <asm/div64.h>
 #include "cifsfs.h"
@@ -3351,6 +3351,38 @@ void cifs_oplock_break(struct work_struct *work)
 	cifs_done_oplock_break(cinode);
 }
 
+#ifdef CONFIG_SWAP
+static void cifs_swap_submit_write(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct iov_iter iter;
+	int ret;
+
+	swap_fs_prepare_rw(ctx, WRITE, &iter);
+	ret = netfs_unbuffered_write_iter_locked(&sio->iocb, &iter, NULL);
+	if (ret != -EIOCBQUEUED)
+		sio->iocb.ki_complete(&sio->iocb, ret);
+}
+
+static void cifs_swap_submit_read(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct iov_iter iter;
+	int ret;
+
+	swap_fs_prepare_rw(ctx, READ, &iter);
+	ret = netfs_unbuffered_read_iter_locked(&sio->iocb, &iter);
+	if (ret != -EIOCBQUEUED)
+		sio->iocb.ki_complete(&sio->iocb, ret);
+}
+
+static const struct swap_ops cifs_swap_ops = {
+	.flags			= SWAP_OPS_F_REQUIRE_NOFS,
+	.submit_write		= cifs_swap_submit_write,
+	.submit_read		= cifs_swap_submit_read,
+	.can_merge		= swap_fs_can_merge,
+};
+
 static int cifs_swap_activate(struct swap_info_struct *sis,
 			      struct file *swap_file, sector_t *span)
 {
@@ -3361,7 +3393,7 @@ static int cifs_swap_activate(struct swap_info_struct *sis,
 
 	cifs_dbg(FYI, "swap activate\n");
 
-	if (!swap_file->f_mapping->a_ops->swap_rw)
+	if (swap_file->f_mapping->a_ops != &cifs_addr_ops)
 		/* Cannot support swap */
 		return -EINVAL;
 
@@ -3392,7 +3424,7 @@ static int cifs_swap_activate(struct swap_info_struct *sis,
 	 * but we could add call to grab a byte range lock to prevent others
 	 * from reading or writing the file
 	 */
-	return swap_fs_activate(sis);
+	return swap_fs_activate(sis, &cifs_swap_ops);
 }
 
 static void cifs_swap_deactivate(struct file *file)
@@ -3408,26 +3440,10 @@ static void cifs_swap_deactivate(struct file *file)
 
 	/* do we need to unpin (or unlock) the file */
 }
-
-/**
- * cifs_swap_rw - SMB3 address space operation for swap I/O
- * @iocb: target I/O control block
- * @iter: I/O buffer
- *
- * Perform IO to the swap-file.  This is much like direct IO.
- */
-static int cifs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
-{
-	ssize_t ret;
-
-	if (iov_iter_rw(iter) == READ)
-		ret = netfs_unbuffered_read_iter_locked(iocb, iter);
-	else
-		ret = netfs_unbuffered_write_iter_locked(iocb, iter, NULL);
-	if (ret < 0)
-		return ret;
-	return 0;
-}
+#else
+#define cifs_swap_activate	NULL
+#define cifs_swap_deactivate	NULL
+#endif /* CONFIG_SWAP */
 
 const struct address_space_operations cifs_addr_ops = {
 	.read_folio	= netfs_read_folio,
@@ -3444,7 +3460,6 @@ const struct address_space_operations cifs_addr_ops = {
 	 */
 	.swap_activate	= cifs_swap_activate,
 	.swap_deactivate = cifs_swap_deactivate,
-	.swap_rw = cifs_swap_rw,
 };
 
 /*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 50ce731a2b78..87b5e9957c00 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -438,7 +438,6 @@ struct address_space_operations {
 	int (*swap_activate)(struct swap_info_struct *sis, struct file *file,
 				sector_t *span);
 	void (*swap_deactivate)(struct file *file);
-	int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
 };
 
 extern const struct address_space_operations empty_aops;
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index ec17e602c979..764056498eba 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -548,7 +548,6 @@ static inline const struct cred *nfs_file_cred(struct file *file)
 /*
  * linux/fs/nfs/direct.c
  */
-int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter);
 ssize_t nfs_file_direct_read(struct kiocb *iocb,
 			     struct iov_iter *iter, bool swap);
 ssize_t nfs_file_direct_write(struct kiocb *iocb,
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 0544b2ec4c56..d8584f53a6e4 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -334,8 +334,6 @@ extern void __meminit kswapd_run(int nid);
 extern void __meminit kswapd_stop(int nid);
 
 #ifdef CONFIG_SWAP
-
-int swap_fs_activate(struct swap_info_struct *sis);
 int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 		unsigned long nr_pages, sector_t start_block);
 int generic_swapfile_activate(struct swap_info_struct *, struct file *,
@@ -461,10 +459,6 @@ static inline bool folio_free_swap(struct folio *folio)
 	return false;
 }
 
-static inline int swap_fs_activate(struct swap_info_struct *sis)
-{
-	return -EINVAL;
-}
 static inline int add_swap_extent(struct swap_info_struct *sis,
 				  unsigned long start_page,
 				  unsigned long nr_pages, sector_t start_block)
diff --git a/include/linux/swap_ops.h b/include/linux/swap_ops.h
index e92b4f532604..57ac6c703f68 100644
--- a/include/linux/swap_ops.h
+++ b/include/linux/swap_ops.h
@@ -36,4 +36,9 @@ struct swap_ops {
 	void (*submit_read)(struct swap_io_ctx *ctx);
 };
 
+void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter);
+bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio,
+		size_t prev_folio_size, int rw);
+int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops);
+
 #endif /* _MM_SWAP_OPS_H */
diff --git a/mm/page_io.c b/mm/page_io.c
index e741e67d6592..88962571cb93 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -650,11 +650,9 @@ const struct swap_ops swap_bdev_ops = {
 	.can_merge		= swap_bdev_can_merge,
 };
 
-static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
+void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter)
 {
 	struct swap_iocb *sio = ctx->sio;
-	struct iov_iter iter;
-	int ret;
 
 	init_sync_kiocb(&sio->iocb, ctx->sis->swap_file);
 	sio->iocb.ki_pos = swap_dev_pos(bvec_folio(&sio->bvecs[0])->swap);
@@ -663,40 +661,22 @@ static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
 	else
 		sio->iocb.ki_complete = swap_fs_read_complete;
 
-	iov_iter_bvec(&iter, rw == WRITE ? ITER_SOURCE : ITER_DEST,
+	iov_iter_bvec(iter, rw == WRITE ? ITER_SOURCE : ITER_DEST,
 			sio->bvecs, sio->nr_bvecs, sio->len);
-	ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &iter);
-	if (ret != -EIOCBQUEUED)
-		sio->iocb.ki_complete(&sio->iocb, ret);
 }
+EXPORT_SYMBOL_GPL(swap_fs_prepare_rw);
 
-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,
+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;
 }
+EXPORT_SYMBOL_GPL(swap_fs_can_merge);
 
-static const struct swap_ops swap_fs_ops = {
-	.flags			= SWAP_OPS_F_REQUIRE_NOFS,
-	.submit_write		= swap_fs_submit_write,
-	.submit_read		= swap_fs_submit_read,
-	.can_merge		= swap_fs_can_merge,
-};
-
-int swap_fs_activate(struct swap_info_struct *sis)
+int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops)
 {
-	sis->ops = &swap_fs_ops;
+	sis->ops = ops;
 	return add_swap_extent(sis, 0, sis->max, 0);
 }
 EXPORT_SYMBOL_GPL(swap_fs_activate);
-- 
2.53.0

Re: [PATCH 3/3] mm/swap: move swap_ops into file systems for file system-based swap

[Chris Li]

On Wed, Jul 22, 2026 at 6:07 AM Christoph Hellwig <hch@lst.de> wrote:
>
> Currently swap to and from file systems goes through two indirect calls
> between the swap ops and the swap_rw method.  Reduce this by directly
> providing the swap_ops from the file system.
>
> For this refactor swap_fs_submit into a swap_fs_prepare_rw helper that
> initializes the iov_iter on the callers stack so that file systems can
> call it directly, and use that to initialize file system specific ops
> in NFS and the SMB client, which then get passed to swap_fs_activate.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I am very happy to see the direction this patch is going. Now I see
how to get rid of the double indirection.

You convinced me with flying colors.

Acked-by: Chris Li <chrisl@kernel.org>

Chris


> ---
>  Documentation/filesystems/locking.rst |  9 +---
>  Documentation/filesystems/vfs.rst     |  8 +---
>  fs/nfs/direct.c                       | 20 ---------
>  fs/nfs/file.c                         | 42 ++++++++++++++++--
>  fs/smb/client/file.c                  | 63 +++++++++++++++++----------
>  include/linux/fs.h                    |  1 -
>  include/linux/nfs_fs.h                |  1 -
>  include/linux/swap.h                  |  6 ---
>  include/linux/swap_ops.h              |  5 +++
>  mm/page_io.c                          | 34 +++------------
>  10 files changed, 93 insertions(+), 96 deletions(-)
>
> diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
> index 1a50d41a39a1..f58a8d7d5897 100644
> --- a/Documentation/filesystems/locking.rst
> +++ b/Documentation/filesystems/locking.rst
> @@ -266,7 +266,6 @@ prototypes::
>         int (*error_remove_folio)(struct address_space *, struct folio *);
>         int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
>         int (*swap_deactivate)(struct file *);
> -       int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
>
>  locking rules:
>         All except dirty_folio and free_folio may block
> @@ -291,7 +290,6 @@ is_partially_uptodate:      yes
>  error_remove_folio:    yes
>  swap_activate:         no
>  swap_deactivate:       no
> -swap_rw:               yes, unlocks
>  ====================== ======================== =========      ===============
>
>  ->write_begin(), ->write_end() and ->read_folio() may be called from
> @@ -355,15 +353,12 @@ should perform any validation and preparation necessary to ensure that
>  writes can be performed with minimal memory allocation.  It should call
>  add_swap_extent(), or the helper iomap_swapfile_activate(), and return
>  the number of extents added.  If IO should be submitted through
> -->swap_rw(), it should call swap_fs_activate, otherwise IO will be submitted
> -directly to the block device ``sis->bdev``.
> +the file system it should call swap_fs_activate, otherwise IO will be
> +submitted directly to the block device ``sis->bdev``.
>
>  ->swap_deactivate() will be called in the sys_swapoff()
>  path after ->swap_activate() returned success.
>
> -->swap_rw will be called for swap IO if swap_fs_activate was called by
> -->swap_activate().
> -
>  file_lock_operations
>  ====================
>
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index e7677423a20f..c437a342d4f3 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -776,7 +776,6 @@ cache in your filesystem.  The following members are defined:
>                 int (*error_remove_folio)(struct mapping *mapping, struct folio *);
>                 int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span)
>                 int (*swap_deactivate)(struct file *);
> -               int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
>         };
>
>  ``read_folio``
> @@ -977,16 +976,13 @@ cache in your filesystem.  The following members are defined:
>         can be performed with minimal memory allocation.  It should call
>         add_swap_extent(), or the helper iomap_swapfile_activate(), and
>         return the number of extents added.  If IO should be submitted
> -       through ->swap_rw(), it should call swap_fs_activate, otherwise IO will
> -       be submitted directly to the block device ``sis->bdev``.
> +       through the file system it should call swap_fs_activate, otherwise IO
> +       will be submitted directly to the block device ``sis->bdev``.
>
>  ``swap_deactivate``
>         Called during swapoff on files where swap_activate was
>         successful.
>
> -``swap_rw``
> -       Called to read or write swap pages when swap_fs_activate was called.
> -
>  The File Object
>  ===============
>
> diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
> index e626c72495e6..ccafdc1ce64d 100644
> --- a/fs/nfs/direct.c
> +++ b/fs/nfs/direct.c
> @@ -145,26 +145,6 @@ static void nfs_direct_file_adjust_size_locked(struct inode *inode,
>         }
>  }
>
> -/**
> - * nfs_swap_rw - NFS address space operation for swap I/O
> - * @iocb: target I/O control block
> - * @iter: I/O buffer
> - *
> - * Perform IO to the swap-file.  This is much like direct IO.
> - */
> -int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
> -{
> -       ssize_t ret;
> -
> -       if (iov_iter_rw(iter) == READ)
> -               ret = nfs_file_direct_read(iocb, iter, true);
> -       else
> -               ret = nfs_file_direct_write(iocb, iter, true);
> -       if (ret < 0)
> -               return ret;
> -       return 0;
> -}
> -
>  static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
>  {
>         unsigned int i;
> diff --git a/fs/nfs/file.c b/fs/nfs/file.c
> index 851d93a09988..e1bdd10b35f1 100644
> --- a/fs/nfs/file.c
> +++ b/fs/nfs/file.c
> @@ -29,9 +29,8 @@
>  #include <linux/pagemap.h>
>  #include <linux/gfp.h>
>  #include <linux/rmap.h>
> -#include <linux/swap.h>
>  #include <linux/compaction.h>
> -
> +#include <linux/swap_ops.h>
>  #include <linux/uaccess.h>
>  #include <linux/filelock.h>
>
> @@ -575,6 +574,38 @@ static int nfs_launder_folio(struct folio *folio)
>         return ret;
>  }
>
> +#ifdef CONFIG_SWAP
> +static void nfs_swap_submit_write(struct swap_io_ctx *ctx)
> +{
> +       struct swap_iocb *sio = ctx->sio;
> +       struct iov_iter iter;
> +       int ret;
> +
> +       swap_fs_prepare_rw(ctx, WRITE, &iter);
> +       ret = nfs_file_direct_write(&sio->iocb, &iter, true);
> +       if (ret != -EIOCBQUEUED)
> +               sio->iocb.ki_complete(&sio->iocb, ret);
> +}
> +
> +static void nfs_swap_submit_read(struct swap_io_ctx *ctx)
> +{
> +       struct swap_iocb *sio = ctx->sio;
> +       struct iov_iter iter;
> +       int ret;
> +
> +       swap_fs_prepare_rw(ctx, READ, &iter);
> +       ret = nfs_file_direct_read(&sio->iocb, &iter, true);
> +       if (ret != -EIOCBQUEUED)
> +               sio->iocb.ki_complete(&sio->iocb, ret);
> +}
> +
> +static const struct swap_ops nfs_swap_ops = {
> +       .flags                  = SWAP_OPS_F_REQUIRE_NOFS,
> +       .submit_write           = nfs_swap_submit_write,
> +       .submit_read            = nfs_swap_submit_read,
> +       .can_merge              = swap_fs_can_merge,
> +};
> +
>  static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
>                                                 sector_t *span)
>  {
> @@ -597,7 +628,7 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
>         ret = rpc_clnt_swap_activate(clnt);
>         if (ret)
>                 return ret;
> -       ret = swap_fs_activate(sis);
> +       ret = swap_fs_activate(sis, &nfs_swap_ops);
>         if (ret < 0) {
>                 rpc_clnt_swap_deactivate(clnt);
>                 return ret;
> @@ -620,6 +651,10 @@ static void nfs_swap_deactivate(struct file *file)
>         if (cl->rpc_ops->disable_swap)
>                 cl->rpc_ops->disable_swap(file_inode(file));
>  }
> +#else
> +#define nfs_swap_activate      NULL
> +#define nfs_swap_deactivate    NULL
> +#endif /* CONFIG_SWAP */
>
>  const struct address_space_operations nfs_file_aops = {
>         .read_folio = nfs_read_folio,
> @@ -636,7 +671,6 @@ const struct address_space_operations nfs_file_aops = {
>         .error_remove_folio = generic_error_remove_folio,
>         .swap_activate = nfs_swap_activate,
>         .swap_deactivate = nfs_swap_deactivate,
> -       .swap_rw = nfs_swap_rw,
>  };
>
>  /*
> diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
> index 081bb16abeb4..190e24199fa1 100644
> --- a/fs/smb/client/file.c
> +++ b/fs/smb/client/file.c
> @@ -20,7 +20,7 @@
>  #include <linux/delay.h>
>  #include <linux/mount.h>
>  #include <linux/slab.h>
> -#include <linux/swap.h>
> +#include <linux/swap_ops.h>
>  #include <linux/mm.h>
>  #include <asm/div64.h>
>  #include "cifsfs.h"
> @@ -3351,6 +3351,38 @@ void cifs_oplock_break(struct work_struct *work)
>         cifs_done_oplock_break(cinode);
>  }
>
> +#ifdef CONFIG_SWAP
> +static void cifs_swap_submit_write(struct swap_io_ctx *ctx)
> +{
> +       struct swap_iocb *sio = ctx->sio;
> +       struct iov_iter iter;
> +       int ret;
> +
> +       swap_fs_prepare_rw(ctx, WRITE, &iter);
> +       ret = netfs_unbuffered_write_iter_locked(&sio->iocb, &iter, NULL);
> +       if (ret != -EIOCBQUEUED)
> +               sio->iocb.ki_complete(&sio->iocb, ret);
> +}
> +
> +static void cifs_swap_submit_read(struct swap_io_ctx *ctx)
> +{
> +       struct swap_iocb *sio = ctx->sio;
> +       struct iov_iter iter;
> +       int ret;
> +
> +       swap_fs_prepare_rw(ctx, READ, &iter);
> +       ret = netfs_unbuffered_read_iter_locked(&sio->iocb, &iter);
> +       if (ret != -EIOCBQUEUED)
> +               sio->iocb.ki_complete(&sio->iocb, ret);
> +}
> +
> +static const struct swap_ops cifs_swap_ops = {
> +       .flags                  = SWAP_OPS_F_REQUIRE_NOFS,
> +       .submit_write           = cifs_swap_submit_write,
> +       .submit_read            = cifs_swap_submit_read,
> +       .can_merge              = swap_fs_can_merge,
> +};
> +
>  static int cifs_swap_activate(struct swap_info_struct *sis,
>                               struct file *swap_file, sector_t *span)
>  {
> @@ -3361,7 +3393,7 @@ static int cifs_swap_activate(struct swap_info_struct *sis,
>
>         cifs_dbg(FYI, "swap activate\n");
>
> -       if (!swap_file->f_mapping->a_ops->swap_rw)
> +       if (swap_file->f_mapping->a_ops != &cifs_addr_ops)
>                 /* Cannot support swap */
>                 return -EINVAL;
>
> @@ -3392,7 +3424,7 @@ static int cifs_swap_activate(struct swap_info_struct *sis,
>          * but we could add call to grab a byte range lock to prevent others
>          * from reading or writing the file
>          */
> -       return swap_fs_activate(sis);
> +       return swap_fs_activate(sis, &cifs_swap_ops);
>  }
>
>  static void cifs_swap_deactivate(struct file *file)
> @@ -3408,26 +3440,10 @@ static void cifs_swap_deactivate(struct file *file)
>
>         /* do we need to unpin (or unlock) the file */
>  }
> -
> -/**
> - * cifs_swap_rw - SMB3 address space operation for swap I/O
> - * @iocb: target I/O control block
> - * @iter: I/O buffer
> - *
> - * Perform IO to the swap-file.  This is much like direct IO.
> - */
> -static int cifs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
> -{
> -       ssize_t ret;
> -
> -       if (iov_iter_rw(iter) == READ)
> -               ret = netfs_unbuffered_read_iter_locked(iocb, iter);
> -       else
> -               ret = netfs_unbuffered_write_iter_locked(iocb, iter, NULL);
> -       if (ret < 0)
> -               return ret;
> -       return 0;
> -}
> +#else
> +#define cifs_swap_activate     NULL
> +#define cifs_swap_deactivate   NULL
> +#endif /* CONFIG_SWAP */
>
>  const struct address_space_operations cifs_addr_ops = {
>         .read_folio     = netfs_read_folio,
> @@ -3444,7 +3460,6 @@ const struct address_space_operations cifs_addr_ops = {
>          */
>         .swap_activate  = cifs_swap_activate,
>         .swap_deactivate = cifs_swap_deactivate,
> -       .swap_rw = cifs_swap_rw,
>  };
>
>  /*
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 50ce731a2b78..87b5e9957c00 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -438,7 +438,6 @@ struct address_space_operations {
>         int (*swap_activate)(struct swap_info_struct *sis, struct file *file,
>                                 sector_t *span);
>         void (*swap_deactivate)(struct file *file);
> -       int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
>  };
>
>  extern const struct address_space_operations empty_aops;
> diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
> index ec17e602c979..764056498eba 100644
> --- a/include/linux/nfs_fs.h
> +++ b/include/linux/nfs_fs.h
> @@ -548,7 +548,6 @@ static inline const struct cred *nfs_file_cred(struct file *file)
>  /*
>   * linux/fs/nfs/direct.c
>   */
> -int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter);
>  ssize_t nfs_file_direct_read(struct kiocb *iocb,
>                              struct iov_iter *iter, bool swap);
>  ssize_t nfs_file_direct_write(struct kiocb *iocb,
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 0544b2ec4c56..d8584f53a6e4 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -334,8 +334,6 @@ extern void __meminit kswapd_run(int nid);
>  extern void __meminit kswapd_stop(int nid);
>
>  #ifdef CONFIG_SWAP
> -
> -int swap_fs_activate(struct swap_info_struct *sis);
>  int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
>                 unsigned long nr_pages, sector_t start_block);
>  int generic_swapfile_activate(struct swap_info_struct *, struct file *,
> @@ -461,10 +459,6 @@ static inline bool folio_free_swap(struct folio *folio)
>         return false;
>  }
>
> -static inline int swap_fs_activate(struct swap_info_struct *sis)
> -{
> -       return -EINVAL;
> -}
>  static inline int add_swap_extent(struct swap_info_struct *sis,
>                                   unsigned long start_page,
>                                   unsigned long nr_pages, sector_t start_block)
> diff --git a/include/linux/swap_ops.h b/include/linux/swap_ops.h
> index e92b4f532604..57ac6c703f68 100644
> --- a/include/linux/swap_ops.h
> +++ b/include/linux/swap_ops.h
> @@ -36,4 +36,9 @@ struct swap_ops {
>         void (*submit_read)(struct swap_io_ctx *ctx);
>  };
>
> +void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter);
> +bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio,
> +               size_t prev_folio_size, int rw);
> +int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops);
> +
>  #endif /* _MM_SWAP_OPS_H */
> diff --git a/mm/page_io.c b/mm/page_io.c
> index e741e67d6592..88962571cb93 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -650,11 +650,9 @@ const struct swap_ops swap_bdev_ops = {
>         .can_merge              = swap_bdev_can_merge,
>  };
>
> -static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
> +void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter)
>  {
>         struct swap_iocb *sio = ctx->sio;
> -       struct iov_iter iter;
> -       int ret;
>
>         init_sync_kiocb(&sio->iocb, ctx->sis->swap_file);
>         sio->iocb.ki_pos = swap_dev_pos(bvec_folio(&sio->bvecs[0])->swap);
> @@ -663,40 +661,22 @@ static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
>         else
>                 sio->iocb.ki_complete = swap_fs_read_complete;
>
> -       iov_iter_bvec(&iter, rw == WRITE ? ITER_SOURCE : ITER_DEST,
> +       iov_iter_bvec(iter, rw == WRITE ? ITER_SOURCE : ITER_DEST,
>                         sio->bvecs, sio->nr_bvecs, sio->len);
> -       ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &iter);
> -       if (ret != -EIOCBQUEUED)
> -               sio->iocb.ki_complete(&sio->iocb, ret);
>  }
> +EXPORT_SYMBOL_GPL(swap_fs_prepare_rw);
>
> -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,
> +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;
>  }
> +EXPORT_SYMBOL_GPL(swap_fs_can_merge);
>
> -static const struct swap_ops swap_fs_ops = {
> -       .flags                  = SWAP_OPS_F_REQUIRE_NOFS,
> -       .submit_write           = swap_fs_submit_write,
> -       .submit_read            = swap_fs_submit_read,
> -       .can_merge              = swap_fs_can_merge,
> -};
> -
> -int swap_fs_activate(struct swap_info_struct *sis)
> +int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops)
>  {
> -       sis->ops = &swap_fs_ops;
> +       sis->ops = ops;
>         return add_swap_extent(sis, 0, sis->max, 0);
>  }
>  EXPORT_SYMBOL_GPL(swap_fs_activate);
> --
> 2.53.0
>

swap_ops updates v2

[Christoph Hellwig]

Hi all,

this series is a follow on to the swap ops series now in mm-unstable.

The first patch reintroduces direct folio writes for synchronous
swap files, the other two remove the double indirect for file
system based swap.

Changes since v1:
 - include swap_ops.h in zswap.c
 - fix a commit message typo
 - add a commit log blurb to mention there are not functional changes in
   patch 2

[PATCH 1/3] mm/swap: revert to single-folio writes for synchronous swap devices

[Christoph Hellwig]

Kairui Song reported that zram benefits from submitting each folio
directly instead of batching up I/O because the classic LRU scanning
benefits from clearing the folio writeback bit in the scan loop.

Accommodate that by kicking off writes for synchronous devices for
each iteration.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Usama Arif <usama.arif@linux.dev>
Acked-by: Chris Li <chrisl@kernel.org>
---
 mm/page_io.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index e4fa7ffffe8b..c984a4023a65 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -358,7 +358,16 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
 	}
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+
+	/*
+	 * Write out the iocb if we filled it, or if the device is synchronous.
+	 *
+	 * The latter is to work around expectations in the classic LRU code
+	 * which make synchronous clearing of the folio writeback flag in the
+	 * reclaim path beneficial.
+	 */
+	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
+	    (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
 		if (rw == WRITE)
 			swap_write_submit(ctx);
 		else
-- 
2.53.0