From: Baoquan He <baoquan.he@linux.dev>
To: linux-mm@kvack.org
Cc: akpm@linux-foundation.org, chrisl@kernel.org,
usama.arif@linux.dev, baohua@kernel.org, kasong@tencent.com,
nphamcs@gmail.com, shikemeng@huaweicloud.com,
youngjun.park@lge.com, hch@infradead.org,
linux-kernel@vger.kernel.org, Baoquan He <baoquan.he@linux.dev>
Subject: [PATCH v7 1/3] mm/swap: use swap_ops to register swap device's methods
Date: Fri, 15 May 2026 09:57:35 +0800 [thread overview]
Message-ID: <20260515015737.890994-2-baoquan.he@linux.dev> (raw)
In-Reply-To: <20260515015737.890994-1-baoquan.he@linux.dev>
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 operations adapted into swap_ops.
Suggested-by: Chris Li <chrisl@kernel.org>
Signed-off-by: Baoquan He <baoquan.he@linux.dev>
---
include/linux/swap.h | 3 ++
mm/page_io.c | 104 +++++++++++++++++++++++++------------------
mm/swap.h | 10 ++++-
mm/swapfile.c | 9 ++++
mm/zswap.c | 2 +-
5 files changed, 83 insertions(+), 45 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 7a09df6977a5..0d045fc8ec35 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -20,6 +20,8 @@ struct notifier_block;
struct bio;
+struct swap_ops;
+
#define SWAP_FLAG_PREFER 0x8000 /* set if swap priority specified */
#define SWAP_FLAG_PRIO_MASK 0x7fff
#define SWAP_FLAG_DISCARD 0x10000 /* enable discard for swap */
@@ -282,6 +284,7 @@ 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 70cea9e24d2f..2b520af88376 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -240,6 +240,9 @@ 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);
+
+ VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio);
if (folio_free_swap(folio))
goto out_unlock;
@@ -285,7 +288,7 @@ int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
}
rcu_read_unlock();
- __swap_writepage(folio, swap_plug);
+ sis->ops->write_folio(sis, folio, swap_plug);
return 0;
out_unlock:
folio_unlock(folio);
@@ -375,10 +378,11 @@ 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);
@@ -411,8 +415,9 @@ 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;
@@ -431,8 +436,9 @@ 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;
@@ -448,29 +454,6 @@ 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,
- * 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,
- * 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;
@@ -539,9 +522,10 @@ 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);
@@ -573,8 +557,9 @@ 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;
@@ -595,8 +580,9 @@ 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;
@@ -610,6 +596,44 @@ static void swap_read_folio_bdev_async(struct folio *folio,
submit_bio(bio);
}
+static const struct swap_ops bdev_fs_swap_ops = {
+ .read_folio = swap_read_folio_fs,
+ .write_folio = swap_writepage_fs,
+};
+
+static const struct swap_ops bdev_sync_swap_ops = {
+ .read_folio = swap_read_folio_bdev_sync,
+ .write_folio = swap_writepage_bdev_sync,
+};
+
+static const struct swap_ops bdev_async_swap_ops = {
+ .read_folio = swap_read_folio_bdev_async,
+ .write_folio = swap_writepage_bdev_async,
+};
+
+int init_swap_ops(struct swap_info_struct *sis)
+{
+ /*
+ * ->flags can be updated non-atomically, 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, 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;
+
+ if (!sis->ops || !sis->ops->read_folio || !sis->ops->write_folio)
+ return -EINVAL;
+
+ return 0;
+}
+
void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
{
struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
@@ -644,13 +668,7 @@ 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);
- }
+ sis->ops->read_folio(sis, folio, plug);
finish:
if (workingset) {
diff --git a/mm/swap.h b/mm/swap.h
index a77016f2423b..8d4375f91632 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -217,6 +217,15 @@ extern void __swap_cluster_free_entries(struct swap_info_struct *si,
/* linux/mm/page_io.c */
int sio_pool_init(void);
struct swap_iocb;
+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 init_swap_ops(struct swap_info_struct *sis);
void swap_read_folio(struct folio *folio, struct swap_iocb **plug);
void __swap_read_unplug(struct swap_iocb *plug);
static inline void swap_read_unplug(struct swap_iocb *plug)
@@ -226,7 +235,6 @@ 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/swapfile.c b/mm/swapfile.c
index 9174f1eeffb0..29ae79d0fa2e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3597,6 +3597,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
}
}
+ /*
+ * init_swap_ops() sets si->ops based on flags. It does not need
+ * swapon_mutex, and must complete before enable_swap_info()
+ * exposes the device.
+ */
+ error = init_swap_ops(si);
+ if (error)
+ goto bad_swap_unlock_inode;
+
error = zswap_swapon(si->type, maxpages);
if (error)
goto bad_swap_unlock_inode;
diff --git a/mm/zswap.c b/mm/zswap.c
index 4b5149173b0e..192401f46de4 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1054,7 +1054,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
folio_set_reclaim(folio);
/* start writeback */
- __swap_writepage(folio, NULL);
+ si->ops->write_folio(si, folio, NULL);
out:
if (ret && ret != -EEXIST) {
--
2.52.0
next prev parent reply other threads:[~2026-05-15 1:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-15 1:57 [PATCH v7 0/3] [PATCH v7 0/3] mm/swap: use swap_ops to register swap device's methods Baoquan He
2026-05-15 1:57 ` Baoquan He [this message]
2026-05-15 1:57 ` [PATCH v7 2/3] mm/page_io.c: rename page_io functions to consistent naming Baoquan He
2026-05-15 1:57 ` [PATCH v7 3/3] mm/swap: add unplug callback to swap_ops to fix leaky abstraction Baoquan He
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260515015737.890994-2-baoquan.he@linux.dev \
--to=baoquan.he@linux.dev \
--cc=akpm@linux-foundation.org \
--cc=baohua@kernel.org \
--cc=chrisl@kernel.org \
--cc=hch@infradead.org \
--cc=kasong@tencent.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=nphamcs@gmail.com \
--cc=shikemeng@huaweicloud.com \
--cc=usama.arif@linux.dev \
--cc=youngjun.park@lge.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox