[PATCH 0/3] mm/swap: use swap_ops to register swap device's methods

[PATCH 0/3] mm/swap: use swap_ops to register swap device's methods

[Baoquan He]

This can simplify the code logic and benefit any new type of swap device
added later.

And also do renaming in this patchset:
-------
   file renaming:
   ---
   mm/page_io.c to mm/swap_io.c

   function renaming:
   ---
   swap_writepage_* to swap_write_folio_* in file mm/swap_io.c 


Baoquan He (3):
  mm/swap: rename mm/page_io.c to mm/swap_io.c
  mm/swap: use swap_ops to register swap device's methods
  mm/swap_io.c: rename swap_writepage_* to swap_write_folio_*

 MAINTAINERS                 |   2 +-
 include/linux/swap.h        |  13 +++++
 mm/Makefile                 |   2 +-
 mm/swap.h                   |   3 +-
 mm/{page_io.c => swap_io.c} | 104 +++++++++++++++++++++---------------
 mm/swapfile.c               |   2 +
 mm/zswap.c                  |   3 +-
 7 files changed, 80 insertions(+), 49 deletions(-)
 rename mm/{page_io.c => swap_io.c} (91%)

-- 
2.52.0

[PATCH 1/3] mm/swap: rename mm/page_io.c to mm/swap_io.c

[Baoquan He]

Codes in mm/page_io.c are only related to swap io, it has
nothing to do with other page io.

Rename it to avoid confusion.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 MAINTAINERS                 | 2 +-
 mm/Makefile                 | 2 +-
 mm/swap.h                   | 2 +-
 mm/{page_io.c => swap_io.c} | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)
 rename mm/{page_io.c => swap_io.c} (99%)

diff --git a/MAINTAINERS b/MAINTAINERS
index 14899f1de77e..6ff65f8bc27b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16945,7 +16945,7 @@ F:	Documentation/mm/swap-table.rst
 F:	include/linux/swap.h
 F:	include/linux/swapfile.h
 F:	include/linux/swapops.h
-F:	mm/page_io.c
+F:	mm/swap_io.c
 F:	mm/swap.c
 F:	mm/swap.h
 F:	mm/swap_table.h
diff --git a/mm/Makefile b/mm/Makefile
index 8ad2ab08244e..a65ac900096a 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -75,7 +75,7 @@ ifdef CONFIG_MMU
 	obj-$(CONFIG_ADVISE_SYSCALLS)	+= madvise.o
 endif
 
-obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
+obj-$(CONFIG_SWAP)	+= swap_io.o swap_state.o swapfile.o
 obj-$(CONFIG_ZSWAP)	+= zswap.o
 obj-$(CONFIG_HAS_DMA)	+= dmapool.o
 obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o hugetlb_sysfs.o hugetlb_sysctl.o
diff --git a/mm/swap.h b/mm/swap.h
index a77016f2423b..161185057993 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -214,7 +214,7 @@ extern void __swap_cluster_free_entries(struct swap_info_struct *si,
 					struct swap_cluster_info *ci,
 					unsigned int ci_off, unsigned int nr_pages);
 
-/* linux/mm/page_io.c */
+/* linux/mm/swap_io.c */
 int sio_pool_init(void);
 struct swap_iocb;
 void swap_read_folio(struct folio *folio, struct swap_iocb **plug);
diff --git a/mm/page_io.c b/mm/swap_io.c
similarity index 99%
rename from mm/page_io.c
rename to mm/swap_io.c
index a2c034660c80..d1cdb10ba133 100644
--- a/mm/page_io.c
+++ b/mm/swap_io.c
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- *  linux/mm/page_io.c
+ *  linux/mm/swap_io.c
  *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *
-- 
2.52.0

[PATCH 2/3] mm/swap: use swap_ops to register swap device's methods

[Baoquan He]

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

Currently there are three types of swap devices: bdev_fs, bdev_sync
and bdev_async, and only operations read_folio and write_folio are
included. In the future, there could be more swap device types added
and more appropriate opeations adapted into swap_ops.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 include/linux/swap.h |  13 ++++++
 mm/swap.h            |   1 -
 mm/swap_io.c         | 102 +++++++++++++++++++++++++------------------
 mm/swapfile.c        |   2 +
 mm/zswap.c           |   3 +-
 5 files changed, 76 insertions(+), 45 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 0effe3cc50f5..448e5e66ec5c 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -19,6 +19,7 @@
 struct notifier_block;
 
 struct bio;
+struct swap_iocb;
 
 struct pagevec;
 
@@ -222,6 +223,17 @@ enum {
 #define SWAP_CLUSTER_MAX_SKIPPED (SWAP_CLUSTER_MAX << 10)
 #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
 
+struct swap_ops {
+	void (*read_folio)(struct swap_info_struct *sis,
+			   struct folio *folio,
+			   struct swap_iocb **plug);
+	void (*write_folio)(struct swap_info_struct *sis,
+			    struct folio *folio,
+			    struct swap_iocb **plug);
+};
+
+int probe_swap_fs(struct swap_info_struct *sis);
+
 /*
  * The first page in the swap file is the swap header, which is always marked
  * bad to prevent it from being allocated as an entry. This also prevents the
@@ -284,6 +296,7 @@ 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 */
+	struct swap_ops *ops;
 };
 
 static inline swp_entry_t page_swap_entry(struct page *page)
diff --git a/mm/swap.h b/mm/swap.h
index 161185057993..c390df3f5889 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -226,7 +226,6 @@ static inline void swap_read_unplug(struct swap_iocb *plug)
 }
 void swap_write_unplug(struct swap_iocb *sio);
 int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug);
-void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug);
 
 /* linux/mm/swap_state.c */
 extern struct address_space swap_space __read_mostly;
diff --git a/mm/swap_io.c b/mm/swap_io.c
index d1cdb10ba133..47077b345ae3 100644
--- a/mm/swap_io.c
+++ b/mm/swap_io.c
@@ -240,6 +240,7 @@ static void swap_zeromap_folio_clear(struct folio *folio)
 int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
 {
 	int ret = 0;
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 
 	if (folio_free_swap(folio))
 		goto out_unlock;
@@ -281,7 +282,8 @@ int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
 		return AOP_WRITEPAGE_ACTIVATE;
 	}
 
-	__swap_writepage(folio, swap_plug);
+	if (sis->ops && sis->ops->write_folio)
+		sis->ops->write_folio(sis, folio, swap_plug);
 	return 0;
 out_unlock:
 	folio_unlock(folio);
@@ -371,10 +373,11 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 	mempool_free(sio, sio_pool);
 }
 
-static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
+static void swap_writepage_fs(struct swap_info_struct *sis,
+			      struct folio *folio,
+			      struct swap_iocb **swap_plug)
 {
 	struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
-	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	struct file *swap_file = sis->swap_file;
 	loff_t pos = swap_dev_pos(folio->swap);
 
@@ -407,8 +410,9 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
 		*swap_plug = sio;
 }
 
-static void swap_writepage_bdev_sync(struct folio *folio,
-		struct swap_info_struct *sis)
+static void swap_writepage_bdev_sync(struct swap_info_struct *sis,
+				     struct folio *folio,
+				     struct swap_iocb **plug)
 {
 	struct bio_vec bv;
 	struct bio bio;
@@ -427,8 +431,9 @@ static void swap_writepage_bdev_sync(struct folio *folio,
 	__end_swap_bio_write(&bio);
 }
 
-static void swap_writepage_bdev_async(struct folio *folio,
-		struct swap_info_struct *sis)
+static void swap_writepage_bdev_async(struct swap_info_struct *sis,
+				      struct folio *folio,
+				      struct swap_iocb **plug)
 {
 	struct bio *bio;
 
@@ -444,29 +449,6 @@ static void swap_writepage_bdev_async(struct folio *folio,
 	submit_bio(bio);
 }
 
-void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
-{
-	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
-
-	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
-	/*
-	 * ->flags can be updated non-atomically (scan_swap_map_slots),
-	 * but that will never affect SWP_FS_OPS, so the data_race
-	 * is safe.
-	 */
-	if (data_race(sis->flags & SWP_FS_OPS))
-		swap_writepage_fs(folio, swap_plug);
-	/*
-	 * ->flags can be updated non-atomically (scan_swap_map_slots),
-	 * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
-	 * is safe.
-	 */
-	else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
-		swap_writepage_bdev_sync(folio, sis);
-	else
-		swap_writepage_bdev_async(folio, sis);
-}
-
 void swap_write_unplug(struct swap_iocb *sio)
 {
 	struct iov_iter from;
@@ -535,9 +517,10 @@ static bool swap_read_folio_zeromap(struct folio *folio)
 	return true;
 }
 
-static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
+static void swap_read_folio_fs(struct swap_info_struct *sis,
+			       struct folio *folio,
+			       struct swap_iocb **plug)
 {
-	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	struct swap_iocb *sio = NULL;
 	loff_t pos = swap_dev_pos(folio->swap);
 
@@ -569,8 +552,9 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 		*plug = sio;
 }
 
-static void swap_read_folio_bdev_sync(struct folio *folio,
-		struct swap_info_struct *sis)
+static void swap_read_folio_bdev_sync(struct swap_info_struct *sis,
+				      struct folio *folio,
+				      struct swap_iocb **plug)
 {
 	struct bio_vec bv;
 	struct bio bio;
@@ -591,8 +575,9 @@ static void swap_read_folio_bdev_sync(struct folio *folio,
 	put_task_struct(current);
 }
 
-static void swap_read_folio_bdev_async(struct folio *folio,
-		struct swap_info_struct *sis)
+static void swap_read_folio_bdev_async(struct swap_info_struct *sis,
+				       struct folio *folio,
+				       struct swap_iocb **plug)
 {
 	struct bio *bio;
 
@@ -606,6 +591,42 @@ static void swap_read_folio_bdev_async(struct folio *folio,
 	submit_bio(bio);
 }
 
+static struct swap_ops bdev_fs_swap_ops = {
+	.read_folio = swap_read_folio_fs,
+	.write_folio = swap_writepage_fs,
+};
+
+static struct swap_ops bdev_sync_swap_ops = {
+	.read_folio = swap_read_folio_bdev_sync,
+	.write_folio = swap_writepage_bdev_sync,
+};
+
+static struct swap_ops bdev_async_swap_ops = {
+	.read_folio = swap_read_folio_bdev_async,
+	.write_folio = swap_writepage_bdev_async,
+};
+
+int probe_swap_fs(struct swap_info_struct *sis)
+{
+	/*
+	 * ->flags can be updated non-atomically (scan_swap_map_slots),
+	 * but that will never affect SWP_FS_OPS, so the data_race
+	 * is safe.
+	 */
+	if (data_race(sis->flags & SWP_FS_OPS))
+		sis->ops = &bdev_fs_swap_ops;
+	/*
+	 * ->flags can be updated non-atomically (scan_swap_map_slots),
+	 * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
+	 * is safe.
+	 */
+	else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
+		sis->ops = &bdev_sync_swap_ops;
+	else
+		sis->ops = &bdev_async_swap_ops;
+	return 0;
+}
+
 void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 {
 	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
@@ -640,13 +661,8 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 	/* We have to read from slower devices. Increase zswap protection. */
 	zswap_folio_swapin(folio);
 
-	if (data_race(sis->flags & SWP_FS_OPS)) {
-		swap_read_folio_fs(folio, plug);
-	} else if (synchronous) {
-		swap_read_folio_bdev_sync(folio, sis);
-	} else {
-		swap_read_folio_bdev_async(folio, sis);
-	}
+	if (sis->ops && sis->ops->read_folio)
+		sis->ops->read_folio(sis, folio, plug);
 
 finish:
 	if (workingset) {
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 915bc93964db..af498f9af328 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3625,6 +3625,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	/* Sets SWP_WRITEOK, resurrect the percpu ref, expose the swap device */
 	enable_swap_info(si);
 
+	probe_swap_fs(si);
+
 	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
 		K(si->pages), name->name, si->prio, nr_extents,
 		K((unsigned long long)span),
diff --git a/mm/zswap.c b/mm/zswap.c
index a399f7a10830..7ce906249c7a 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1055,7 +1055,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	folio_set_reclaim(folio);
 
 	/* start writeback */
-	__swap_writepage(folio, NULL);
+	if (si->ops && si->ops->write_folio)
+		si->ops->write_folio(si, folio, NULL);
 
 out:
 	if (ret && ret != -EEXIST) {
-- 
2.52.0

[PATCH 3/3] mm/swap_io.c: rename swap_writepage_* to swap_write_folio_*

[Baoquan He]

All these swap_writepage_* functions are hanlding passed in folio, but
not page. And this renaming make them consistent with the their
counterpart swap_read_folio_* functions.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/swap_io.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/swap_io.c b/mm/swap_io.c
index 47077b345ae3..ad315b128e36 100644
--- a/mm/swap_io.c
+++ b/mm/swap_io.c
@@ -373,7 +373,7 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
 	mempool_free(sio, sio_pool);
 }
 
-static void swap_writepage_fs(struct swap_info_struct *sis,
+static void swap_write_folio_fs(struct swap_info_struct *sis,
 			      struct folio *folio,
 			      struct swap_iocb **swap_plug)
 {
@@ -410,7 +410,7 @@ static void swap_writepage_fs(struct swap_info_struct *sis,
 		*swap_plug = sio;
 }
 
-static void swap_writepage_bdev_sync(struct swap_info_struct *sis,
+static void swap_write_folio_bdev_sync(struct swap_info_struct *sis,
 				     struct folio *folio,
 				     struct swap_iocb **plug)
 {
@@ -431,7 +431,7 @@ static void swap_writepage_bdev_sync(struct swap_info_struct *sis,
 	__end_swap_bio_write(&bio);
 }
 
-static void swap_writepage_bdev_async(struct swap_info_struct *sis,
+static void swap_write_folio_bdev_async(struct swap_info_struct *sis,
 				      struct folio *folio,
 				      struct swap_iocb **plug)
 {
@@ -593,17 +593,17 @@ static void swap_read_folio_bdev_async(struct swap_info_struct *sis,
 
 static struct swap_ops bdev_fs_swap_ops = {
 	.read_folio = swap_read_folio_fs,
-	.write_folio = swap_writepage_fs,
+	.write_folio = swap_write_folio_fs,
 };
 
 static struct swap_ops bdev_sync_swap_ops = {
 	.read_folio = swap_read_folio_bdev_sync,
-	.write_folio = swap_writepage_bdev_sync,
+	.write_folio = swap_write_folio_bdev_sync,
 };
 
 static struct swap_ops bdev_async_swap_ops = {
 	.read_folio = swap_read_folio_bdev_async,
-	.write_folio = swap_writepage_bdev_async,
+	.write_folio = swap_write_folio_bdev_async,
 };
 
 int probe_swap_fs(struct swap_info_struct *sis)
-- 
2.52.0

Re: [PATCH 1/3] mm/swap: rename mm/page_io.c to mm/swap_io.c

[Barry Song]

On Mon, Mar 2, 2026 at 6:40 PM Baoquan He <bhe@redhat.com> wrote:
>
> Codes in mm/page_io.c are only related to swap io, it has
> nothing to do with other page io.

That is true. Meanwhile, swap.c and swap.h contain a fair
amount of non-swap-related code, such as lru_xxx and even
file-related functions like deactivate_file_folio().

Perhaps we should consider moving these to more
appropriate locations.

>
> Rename it to avoid confusion.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>

Reviewed-by: Barry Song <baohua@kernel.org>

Re: [PATCH 2/3] mm/swap: use swap_ops to register swap device's methods

[Barry Song]

On Mon, Mar 2, 2026 at 6:40 PM Baoquan He <bhe@redhat.com> wrote:
>
> This simplifies codes and makes logic clearer. And also makes later any
> new swap device type being added easier to handle.
>
> Currently there are three types of swap devices: bdev_fs, bdev_sync
> and bdev_async, and only operations read_folio and write_folio are
> included. In the future, there could be more swap device types added
> and more appropriate opeations adapted into swap_ops.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  include/linux/swap.h |  13 ++++++
>  mm/swap.h            |   1 -
>  mm/swap_io.c         | 102 +++++++++++++++++++++++++------------------
>  mm/swapfile.c        |   2 +
>  mm/zswap.c           |   3 +-
>  5 files changed, 76 insertions(+), 45 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 0effe3cc50f5..448e5e66ec5c 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -19,6 +19,7 @@
>  struct notifier_block;
>
>  struct bio;
> +struct swap_iocb;
>
>  struct pagevec;
>
> @@ -222,6 +223,17 @@ enum {
>  #define SWAP_CLUSTER_MAX_SKIPPED (SWAP_CLUSTER_MAX << 10)
>  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
>
> +struct swap_ops {
> +       void (*read_folio)(struct swap_info_struct *sis,
> +                          struct folio *folio,
> +                          struct swap_iocb **plug);
> +       void (*write_folio)(struct swap_info_struct *sis,
> +                           struct folio *folio,
> +                           struct swap_iocb **plug);
> +};
> +
> +int probe_swap_fs(struct swap_info_struct *sis);

Does probe_swap_fs sound a bit odd?
What about init_swap_ops? Not sure if we have a better name.

Do we really want it, along with swap_ops, to live in
include/linux/swap.h? Could it be placed in mm/swap.h instead?

> +
>  /*
>   * The first page in the swap file is the swap header, which is always marked
>   * bad to prevent it from being allocated as an entry. This also prevents the
> @@ -284,6 +296,7 @@ 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 */
> +       struct swap_ops *ops;
>  };
>
>  static inline swp_entry_t page_swap_entry(struct page *page)
> diff --git a/mm/swap.h b/mm/swap.h
> index 161185057993..c390df3f5889 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -226,7 +226,6 @@ static inline void swap_read_unplug(struct swap_iocb *plug)
>  }
>  void swap_write_unplug(struct swap_iocb *sio);
>  int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug);
> -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug);
>
>  /* linux/mm/swap_state.c */
>  extern struct address_space swap_space __read_mostly;
> diff --git a/mm/swap_io.c b/mm/swap_io.c
> index d1cdb10ba133..47077b345ae3 100644
> --- a/mm/swap_io.c
> +++ b/mm/swap_io.c
> @@ -240,6 +240,7 @@ static void swap_zeromap_folio_clear(struct folio *folio)
>  int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
>  {
>         int ret = 0;
> +       struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
>
>         if (folio_free_swap(folio))
>                 goto out_unlock;
> @@ -281,7 +282,8 @@ int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
>                 return AOP_WRITEPAGE_ACTIVATE;
>         }
>
> -       __swap_writepage(folio, swap_plug);
> +       if (sis->ops && sis->ops->write_folio)
> +               sis->ops->write_folio(sis, folio, swap_plug);

Do we want a swap_write_folio() wrapper?

>         return 0;
>  out_unlock:
>         folio_unlock(folio);
> @@ -371,10 +373,11 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
>         mempool_free(sio, sio_pool);
>  }
>
> -static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
> +static void swap_writepage_fs(struct swap_info_struct *sis,
> +                             struct folio *folio,
> +                             struct swap_iocb **swap_plug)
>  {
>         struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
> -       struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
>         struct file *swap_file = sis->swap_file;
>         loff_t pos = swap_dev_pos(folio->swap);
>
> @@ -407,8 +410,9 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
>                 *swap_plug = sio;
>  }
>
> -static void swap_writepage_bdev_sync(struct folio *folio,
> -               struct swap_info_struct *sis)
> +static void swap_writepage_bdev_sync(struct swap_info_struct *sis,
> +                                    struct folio *folio,
> +                                    struct swap_iocb **plug)
>  {
>         struct bio_vec bv;
>         struct bio bio;
> @@ -427,8 +431,9 @@ static void swap_writepage_bdev_sync(struct folio *folio,
>         __end_swap_bio_write(&bio);
>  }
>
> -static void swap_writepage_bdev_async(struct folio *folio,
> -               struct swap_info_struct *sis)
> +static void swap_writepage_bdev_async(struct swap_info_struct *sis,
> +                                     struct folio *folio,
> +                                     struct swap_iocb **plug)
>  {
>         struct bio *bio;
>
> @@ -444,29 +449,6 @@ static void swap_writepage_bdev_async(struct folio *folio,
>         submit_bio(bio);
>  }
>
> -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
> -{
> -       struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> -
> -       VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
> -       /*
> -        * ->flags can be updated non-atomically (scan_swap_map_slots),
> -        * but that will never affect SWP_FS_OPS, so the data_race
> -        * is safe.
> -        */
> -       if (data_race(sis->flags & SWP_FS_OPS))
> -               swap_writepage_fs(folio, swap_plug);
> -       /*
> -        * ->flags can be updated non-atomically (scan_swap_map_slots),
> -        * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
> -        * is safe.
> -        */
> -       else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
> -               swap_writepage_bdev_sync(folio, sis);
> -       else
> -               swap_writepage_bdev_async(folio, sis);
> -}
> -
>  void swap_write_unplug(struct swap_iocb *sio)
>  {
>         struct iov_iter from;
> @@ -535,9 +517,10 @@ static bool swap_read_folio_zeromap(struct folio *folio)
>         return true;
>  }
>
> -static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
> +static void swap_read_folio_fs(struct swap_info_struct *sis,
> +                              struct folio *folio,
> +                              struct swap_iocb **plug)
>  {
> -       struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
>         struct swap_iocb *sio = NULL;
>         loff_t pos = swap_dev_pos(folio->swap);
>
> @@ -569,8 +552,9 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
>                 *plug = sio;
>  }
>
> -static void swap_read_folio_bdev_sync(struct folio *folio,
> -               struct swap_info_struct *sis)
> +static void swap_read_folio_bdev_sync(struct swap_info_struct *sis,
> +                                     struct folio *folio,
> +                                     struct swap_iocb **plug)
>  {
>         struct bio_vec bv;
>         struct bio bio;
> @@ -591,8 +575,9 @@ static void swap_read_folio_bdev_sync(struct folio *folio,
>         put_task_struct(current);
>  }
>
> -static void swap_read_folio_bdev_async(struct folio *folio,
> -               struct swap_info_struct *sis)
> +static void swap_read_folio_bdev_async(struct swap_info_struct *sis,
> +                                      struct folio *folio,
> +                                      struct swap_iocb **plug)
>  {
>         struct bio *bio;
>
> @@ -606,6 +591,42 @@ static void swap_read_folio_bdev_async(struct folio *folio,
>         submit_bio(bio);
>  }
>
> +static struct swap_ops bdev_fs_swap_ops = {
> +       .read_folio = swap_read_folio_fs,
> +       .write_folio = swap_writepage_fs,
> +};

const?

> +
> +static struct swap_ops bdev_sync_swap_ops = {
> +       .read_folio = swap_read_folio_bdev_sync,
> +       .write_folio = swap_writepage_bdev_sync,
> +};

const?

> +
> +static struct swap_ops bdev_async_swap_ops = {
> +       .read_folio = swap_read_folio_bdev_async,
> +       .write_folio = swap_writepage_bdev_async,
> +};

const?

> +
> +int probe_swap_fs(struct swap_info_struct *sis)
> +{
> +       /*
> +        * ->flags can be updated non-atomically (scan_swap_map_slots),
> +        * but that will never affect SWP_FS_OPS, so the data_race
> +        * is safe.
> +        */
> +       if (data_race(sis->flags & SWP_FS_OPS))
> +               sis->ops = &bdev_fs_swap_ops;
> +       /*
> +        * ->flags can be updated non-atomically (scan_swap_map_slots),
> +        * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
> +        * is safe.
> +        */
> +       else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
> +               sis->ops = &bdev_sync_swap_ops;
> +       else
> +               sis->ops = &bdev_async_swap_ops;
> +       return 0;
> +}
> +
>  void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
>  {
>         struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> @@ -640,13 +661,8 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
>         /* We have to read from slower devices. Increase zswap protection. */
>         zswap_folio_swapin(folio);
>
> -       if (data_race(sis->flags & SWP_FS_OPS)) {
> -               swap_read_folio_fs(folio, plug);
> -       } else if (synchronous) {
> -               swap_read_folio_bdev_sync(folio, sis);
> -       } else {
> -               swap_read_folio_bdev_async(folio, sis);
> -       }
> +       if (sis->ops && sis->ops->read_folio)
> +               sis->ops->read_folio(sis, folio, plug);
>
>  finish:
>         if (workingset) {
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 915bc93964db..af498f9af328 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3625,6 +3625,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>         /* Sets SWP_WRITEOK, resurrect the percpu ref, expose the swap device */
>         enable_swap_info(si);
>
> +       probe_swap_fs(si);

Can we move this to enable_swap_info(), or perhaps even
deeper into setup_swap_info()?

> +
>         pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
>                 K(si->pages), name->name, si->prio, nr_extents,
>                 K((unsigned long long)span),
> diff --git a/mm/zswap.c b/mm/zswap.c
> index a399f7a10830..7ce906249c7a 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1055,7 +1055,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
>         folio_set_reclaim(folio);
>
>         /* start writeback */
> -       __swap_writepage(folio, NULL);
> +       if (si->ops && si->ops->write_folio)
> +               si->ops->write_folio(si, folio, NULL);

swap_write_folio() inline wrapper?

>
>  out:
>         if (ret && ret != -EEXIST) {
> --
> 2.52.0
>

Thanks
Barry

Re: [PATCH 3/3] mm/swap_io.c: rename swap_writepage_* to swap_write_folio_*

[Barry Song]

On Mon, Mar 2, 2026 at 6:40 PM Baoquan He <bhe@redhat.com> wrote:
>
> All these swap_writepage_* functions are hanlding passed in folio, but
> not page. And this renaming make them consistent with the their
> counterpart swap_read_folio_* functions.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>

LGTM,

Reviewed-by: Barry Song <baohua@kernel.org>

> ---
>  mm/swap_io.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

Re: [PATCH 2/3] mm/swap: use swap_ops to register swap device's methods

[YoungJun Park]

On Mon, Mar 02, 2026 at 06:40:15PM +0800, Baoquan He wrote:

Hello Baoquan!

...
> +	.read_folio = swap_read_folio_bdev_sync,
> +	.write_folio = swap_writepage_bdev_sync,
> +};
> +
> +static struct swap_ops bdev_async_swap_ops = {
> +	.read_folio = swap_read_folio_bdev_async,
> +	.write_folio = swap_writepage_bdev_async,
> +};
> +
> +int probe_swap_fs(struct swap_info_struct *sis)
> +{
> +	/*
> +	 * ->flags can be updated non-atomically (scan_swap_map_slots),
> +	 * but that will never affect SWP_FS_OPS, so the data_race
> +	 * is safe.
> +	 */
> +	if (data_race(sis->flags & SWP_FS_OPS))
> +		sis->ops = &bdev_fs_swap_ops;
> +	/*
> +	 * ->flags can be updated non-atomically (scan_swap_map_slots),
> +	 * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
> +	 * is safe.
> +	 */

The reference to scan_swap_map_slots appears to be outdated as the
function no longer exists in the current codebase. It might be
better to update this to a more generic term?

If comments are needed to be updated, 
Similar comments in may_enter_fs likely need a similar update
for consistency.

> +	else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO))
> +		sis->ops = &bdev_sync_swap_ops;
> +	else
> +		sis->ops = &bdev_async_swap_ops;
> +	return 0;

it seems return value is not needed.

Thanks 
Youngjun Park