better block swap batching and a different take on swap_ops v3

better block swap batching and a different take on swap_ops v3

[Christoph Hellwig]

Hi all,

this series makes use of the swap_iocb for block as well so that it
doesn't do inefficient single-bio I/O, and then rebases the swap_ops from
Baoquan on top of the now very different method structure.

When running doing kernels builds, which is a workload that doesn't
really do much THP anonymous memory it still gets 2x clustering for
writeout and 1.2x for reading back swap in.  The overall times do
not actually change, though.


Changes since v2:
 - rebased to 7.2-rc2
 - rename swap_add_page to swap_add_folio
 - rename SWAP_OPS_F_NOFS to SWAP_OPS_F_REQUIRE_NOFS and document it
 - improve various commit logs
 - spelling fixes

Changes since v1:
 - drop the memcg accounting for fs backed swap as it can't really
   work as-is
 - change the related refactoring to not create a bisection hazard or
   compile issue with the wrong set of cgroup config options enabled
 - remove a now dead function

Diffstat:
 Documentation/filesystems/locking.rst     |    5 
 Documentation/filesystems/vfs.rst         |    4 
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c |    2 
 drivers/gpu/drm/ttm/ttm_backup.c          |    2 
 fs/nfs/file.c                             |    4 
 fs/smb/client/file.c                      |    4 
 include/linux/shmem_fs.h                  |    5 
 include/linux/swap.h                      |    7 
 include/linux/vm_event_item.h             |    4 
 mm/madvise.c                              |   16 
 mm/page_io.c                              |  585 ++++++++++++++----------------
 mm/shmem.c                                |   18 
 mm/swap.h                                 |   67 +--
 mm/swap_state.c                           |   53 +-
 mm/swapfile.c                             |   11 
 mm/vmscan.c                               |   30 -
 mm/vmstat.c                               |    6 
 mm/zswap.c                                |    4 
 18 files changed, 431 insertions(+), 396 deletions(-)

better block swap batching and a different take on swap_ops v3

[Christoph Hellwig]

Hi all,

this series makes use of the swap_iocb for block as well so that it
doesn't do inefficient single-bio I/O, and then rebases the swap_ops from
Baoquan on top of the now very different method structure.

When running doing kernels builds, which is a workload that doesn't
really do much THP anonymous memory it still gets 2x clustering for
writeout and 1.2x for reading back swap in.  The overall times do
not actually change, though.


Changes since v2:
 - rebased to 7.2-rc2
 - rename swap_add_page to swap_add_folio
 - rename SWAP_OPS_F_NOFS to SWAP_OPS_F_REQUIRE_NOFS and document it
 - improve various commit logs
 - spelling fixes

Changes since v1:
 - drop the memcg accounting for fs backed swap as it can't really
   work as-is
 - change the related refactoring to not create a bisection hazard or
   compile issue with the wrong set of cgroup config options enabled
 - remove a now dead function

Diffstat:
 Documentation/filesystems/locking.rst     |    5 
 Documentation/filesystems/vfs.rst         |    4 
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c |    2 
 drivers/gpu/drm/ttm/ttm_backup.c          |    2 
 fs/nfs/file.c                             |    4 
 fs/smb/client/file.c                      |    4 
 include/linux/shmem_fs.h                  |    5 
 include/linux/swap.h                      |    7 
 include/linux/vm_event_item.h             |    4 
 mm/madvise.c                              |   16 
 mm/page_io.c                              |  585 ++++++++++++++----------------
 mm/shmem.c                                |   18 
 mm/swap.h                                 |   67 +--
 mm/swap_state.c                           |   53 +-
 mm/swapfile.c                             |   11 
 mm/vmscan.c                               |   30 -
 mm/vmstat.c                               |    6 
 mm/zswap.c                                |    4 
 18 files changed, 431 insertions(+), 396 deletions(-)

better block swap batching and a different take on swap_ops v3

[Christoph Hellwig]

Hi all,

this series makes use of the swap_iocb for block as well so that it
doesn't do inefficient single-bio I/O, and then rebases the swap_ops from
Baoquan on top of the now very different method structure.

When running doing kernels builds, which is a workload that doesn't
really do much THP anonymous memory it still gets 2x clustering for
writeout and 1.2x for reading back swap in.  The overall times do
not actually change, though.


Changes since v2:
 - rebased to 7.2-rc2
 - rename swap_add_page to swap_add_folio
 - rename SWAP_OPS_F_NOFS to SWAP_OPS_F_REQUIRE_NOFS and document it
 - improve various commit logs
 - spelling fixes

Changes since v1:
 - drop the memcg accounting for fs backed swap as it can't really
   work as-is
 - change the related refactoring to not create a bisection hazard or
   compile issue with the wrong set of cgroup config options enabled
 - remove a now dead function

Diffstat:
 Documentation/filesystems/locking.rst     |    5 
 Documentation/filesystems/vfs.rst         |    4 
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c |    2 
 drivers/gpu/drm/ttm/ttm_backup.c          |    2 
 fs/nfs/file.c                             |    4 
 fs/smb/client/file.c                      |    4 
 include/linux/shmem_fs.h                  |    5 
 include/linux/swap.h                      |    7 
 include/linux/vm_event_item.h             |    4 
 mm/madvise.c                              |   16 
 mm/page_io.c                              |  585 ++++++++++++++----------------
 mm/shmem.c                                |   18 
 mm/swap.h                                 |   67 +--
 mm/swap_state.c                           |   53 +-
 mm/swapfile.c                             |   11 
 mm/vmscan.c                               |   30 -
 mm/vmstat.c                               |    6 
 mm/zswap.c                                |    4 
 18 files changed, 431 insertions(+), 396 deletions(-)

[PATCH 1/7] shmem: provide a shmem_write_folio wrapper

[Christoph Hellwig]

Provide a wrapper for the shmem abuses in drm to prepare for swap I/O
refactoring by keeping swap_iocb handling entirely contained in mm/.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Chris Li <chrisl@kernel.org>
---
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 2 +-
 drivers/gpu/drm/ttm/ttm_backup.c          | 2 +-
 include/linux/shmem_fs.h                  | 5 +----
 mm/shmem.c                                | 7 ++++++-
 mm/swap.h                                 | 4 ++++
 5 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
index 06543ae60706..ef9440166295 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
@@ -325,7 +325,7 @@ void __shmem_writeback(size_t size, struct address_space *mapping)
 		if (folio_mapped(folio))
 			folio_redirty_for_writepage(&wbc, folio);
 		else
-			error = shmem_writeout(folio, NULL, NULL);
+			error = shmem_write_folio(folio);
 	}
 }
 
diff --git a/drivers/gpu/drm/ttm/ttm_backup.c b/drivers/gpu/drm/ttm/ttm_backup.c
index 81df4cb5606b..c5b813a563e7 100644
--- a/drivers/gpu/drm/ttm/ttm_backup.c
+++ b/drivers/gpu/drm/ttm/ttm_backup.c
@@ -117,7 +117,7 @@ ttm_backup_backup_page(struct file *backup, struct page *page,
 	if (writeback && !folio_mapped(to_folio) &&
 	    folio_clear_dirty_for_io(to_folio)) {
 		folio_set_reclaim(to_folio);
-		ret = shmem_writeout(to_folio, NULL, NULL);
+		ret = shmem_write_folio(to_folio);
 		if (!folio_test_writeback(to_folio))
 			folio_clear_reclaim(to_folio);
 		/*
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index e729b9b0e38d..5663dff53186 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -12,8 +12,6 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/bits.h>
 
-struct swap_iocb;
-
 /* inode in-kernel data */
 
 #ifdef CONFIG_TMPFS_QUOTA
@@ -123,8 +121,7 @@ static inline bool shmem_mapping(const struct address_space *mapping)
 void shmem_unlock_mapping(struct address_space *mapping);
 struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 					pgoff_t index, gfp_t gfp_mask);
-int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
-		struct list_head *folio_list);
+int shmem_write_folio(struct folio *folio);
 void shmem_truncate_range(struct inode *inode, loff_t start, uoff_t end);
 int shmem_unuse(unsigned int type);
 
diff --git a/mm/shmem.c b/mm/shmem.c
index b51f83c970bb..6011a7f729ae 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1736,7 +1736,12 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
 	folio_mark_dirty(folio);
 	return AOP_WRITEPAGE_ACTIVATE;	/* Return with folio locked */
 }
-EXPORT_SYMBOL_GPL(shmem_writeout);
+
+int shmem_write_folio(struct folio *folio)
+{
+	return shmem_writeout(folio, NULL, NULL);
+}
+EXPORT_SYMBOL_GPL(shmem_write_folio);
 
 #if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
 static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
diff --git a/mm/swap.h b/mm/swap.h
index 77d2d14eda42..4f86ef338a60 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -473,4 +473,8 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 }
 
 #endif /* CONFIG_SWAP */
+
+int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
+		struct list_head *folio_list);
+
 #endif /* _MM_SWAP_H */
-- 
2.53.0

[PATCH 2/7] mm/swap: introduce struct swap_io_ctx

[Christoph Hellwig]

Generalize the context currently provided by double pointers to struct
swap_iocb to an on-stack context.  This cleans up the code and prepares
for adding more fields and supporting batching multiple folios into a
single bio for block-based swap as well.

This new swap_io_ctx is required for all functions using it, the old
way of allowing a NULL iocb for some callers is removed to keep the
interface consistent.  To reduce code duplication caused by this, a
new swap_cache_read_folio_sync helper is added to consolidate the
code to call swap_cache_read_folio with a local swap_io_ctx.

The unpug helpers are renamed to use the submit wording as they
are generalized.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
---
 mm/madvise.c    | 16 ++++++-------
 mm/page_io.c    | 60 ++++++++++++++++++++++++++-----------------------
 mm/shmem.c      | 13 +++++++----
 mm/swap.h       | 36 +++++++++++++----------------
 mm/swap_state.c | 53 +++++++++++++++++++++++++------------------
 mm/vmscan.c     | 15 ++++++-------
 mm/zswap.c      |  4 +++-
 7 files changed, 106 insertions(+), 91 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index cd9bb077072c..cd84e993190a 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -188,7 +188,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
 		unsigned long end, struct mm_walk *walk)
 {
 	struct vm_area_struct *vma = walk->private;
-	struct swap_iocb *splug = NULL;
+	struct swap_io_ctx ctx = {};
 	pte_t *ptep = NULL;
 	spinlock_t *ptl;
 	unsigned long addr;
@@ -212,15 +212,15 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
 		pte_unmap_unlock(ptep, ptl);
 		ptep = NULL;
 
-		folio = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
-					     vma, addr, &splug);
+		folio = read_swap_cache_async(&ctx, entry, GFP_HIGHUSER_MOVABLE,
+					vma, addr);
 		if (folio)
 			folio_put(folio);
 	}
 
 	if (ptep)
 		pte_unmap_unlock(ptep, ptl);
-	swap_read_unplug(splug);
+	swap_read_submit(&ctx);
 	cond_resched();
 
 	return 0;
@@ -238,7 +238,7 @@ static void shmem_swapin_range(struct vm_area_struct *vma,
 	XA_STATE(xas, &mapping->i_pages, linear_page_index(vma, start));
 	pgoff_t end_index = linear_page_index(vma, end) - 1;
 	struct folio *folio;
-	struct swap_iocb *splug = NULL;
+	struct swap_io_ctx ctx = {};
 
 	rcu_read_lock();
 	xas_for_each(&xas, folio, end_index) {
@@ -257,15 +257,15 @@ static void shmem_swapin_range(struct vm_area_struct *vma,
 		xas_pause(&xas);
 		rcu_read_unlock();
 
-		folio = read_swap_cache_async(entry, mapping_gfp_mask(mapping),
-					     vma, addr, &splug);
+		folio = read_swap_cache_async(&ctx, entry,
+				mapping_gfp_mask(mapping), vma, addr);
 		if (folio)
 			folio_put(folio);
 
 		rcu_read_lock();
 	}
 	rcu_read_unlock();
-	swap_read_unplug(splug);
+	swap_read_submit(&ctx);
 }
 #endif		/* CONFIG_SWAP */
 
diff --git a/mm/page_io.c b/mm/page_io.c
index b23f494fcc83..fe24a49e034c 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -248,7 +248,7 @@ static void swap_zeromap_folio_clear(struct folio *folio)
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.
  */
-int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
+int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	int ret = 0;
 
@@ -295,7 +295,7 @@ int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug)
 	}
 	rcu_read_unlock();
 
-	__swap_writepage(folio, swap_plug);
+	__swap_writepage(ctx, folio);
 	return 0;
 out_unlock:
 	folio_unlock(folio);
@@ -390,9 +390,9 @@ 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_io_ctx *ctx, struct folio *folio)
 {
-	struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
+	struct swap_iocb *sio = ctx->sio;
 	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);
@@ -403,7 +403,7 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
 	if (sio) {
 		if (sio->iocb.ki_filp != swap_file ||
 		    sio->iocb.ki_pos + sio->len != pos) {
-			swap_write_unplug(sio);
+			swap_write_submit(ctx);
 			sio = NULL;
 		}
 	}
@@ -418,12 +418,11 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
 	sio->nr_bvecs += 1;
-	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) || !swap_plug) {
-		swap_write_unplug(sio);
+	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+		swap_write_submit(ctx);
 		sio = NULL;
 	}
-	if (swap_plug)
-		*swap_plug = sio;
+	ctx->sio = sio;
 }
 
 static void swap_writepage_bdev_sync(struct folio *folio,
@@ -463,7 +462,7 @@ static void swap_writepage_bdev_async(struct folio *folio,
 	submit_bio(bio);
 }
 
-void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
+void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 
@@ -474,7 +473,7 @@ void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
 	 * is safe.
 	 */
 	if (data_race(sis->flags & SWP_FS_OPS))
-		swap_writepage_fs(folio, swap_plug);
+		swap_writepage_fs(ctx, folio);
 	/*
 	 * ->flags can be updated non-atomically,
 	 * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race
@@ -486,16 +485,20 @@ void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
 		swap_writepage_bdev_async(folio, sis);
 }
 
-void swap_write_unplug(struct swap_iocb *sio)
+void swap_write_submit(struct swap_io_ctx *ctx)
 {
+	struct swap_iocb *sio = ctx->sio;
 	struct iov_iter from;
-	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
+	if (!sio)
+		return;
+
 	iov_iter_bvec(&from, ITER_SOURCE, sio->bvecs, sio->nr_bvecs, sio->len);
-	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
+	ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_write_complete(&sio->iocb, ret);
+	ctx->sio = NULL;
 }
 
 static void sio_read_complete(struct kiocb *iocb, long ret)
@@ -587,18 +590,16 @@ 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_io_ctx *ctx, struct folio *folio)
 {
 	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
-	struct swap_iocb *sio = NULL;
+	struct swap_iocb *sio = ctx->sio;
 	loff_t pos = swap_dev_pos(folio->swap);
 
-	if (plug)
-		sio = *plug;
 	if (sio) {
 		if (sio->iocb.ki_filp != sis->swap_file ||
 		    sio->iocb.ki_pos + sio->len != pos) {
-			swap_read_unplug(sio);
+			swap_read_submit(ctx);
 			sio = NULL;
 		}
 	}
@@ -613,12 +614,11 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
 	sio->nr_bvecs += 1;
-	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) || !plug) {
-		swap_read_unplug(sio);
+	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+		swap_read_submit(ctx);
 		sio = NULL;
 	}
-	if (plug)
-		*plug = sio;
+	ctx->sio = sio;
 }
 
 static void swap_read_folio_bdev_sync(struct folio *folio,
@@ -658,7 +658,7 @@ static void swap_read_folio_bdev_async(struct folio *folio,
 	submit_bio(bio);
 }
 
-void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
+void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
 	bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
@@ -693,7 +693,7 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 	zswap_folio_swapin(folio);
 
 	if (data_race(sis->flags & SWP_FS_OPS)) {
-		swap_read_folio_fs(folio, plug);
+		swap_read_folio_fs(ctx, folio);
 	} else if (synchronous) {
 		swap_read_folio_bdev_sync(folio, sis);
 	} else {
@@ -708,14 +708,18 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 	delayacct_swapin_end();
 }
 
-void __swap_read_unplug(struct swap_iocb *sio)
+void swap_read_submit(struct swap_io_ctx *ctx)
 {
+	struct swap_iocb *sio = ctx->sio;
 	struct iov_iter from;
-	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
 	int ret;
 
+	if (!sio)
+		return;
+
 	iov_iter_bvec(&from, ITER_DEST, sio->bvecs, sio->nr_bvecs, sio->len);
-	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
+	ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &from);
 	if (ret != -EIOCBQUEUED)
 		sio_read_complete(&sio->iocb, ret);
+	ctx->sio = NULL;
 }
diff --git a/mm/shmem.c b/mm/shmem.c
index 6011a7f729ae..ac68876cca08 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1582,13 +1582,13 @@ int shmem_unuse(unsigned int type)
 
 /**
  * shmem_writeout - Write the folio to swap
+ * @ctx: swap I/O context
  * @folio: The folio to write
- * @plug: swap plug
  * @folio_list: list to put back folios on split
  *
  * Move the folio from the page cache to the swap cache.
  */
-int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
+int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		struct list_head *folio_list)
 {
 	struct address_space *mapping = folio->mapping;
@@ -1700,7 +1700,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
 		shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));
 
 		BUG_ON(folio_mapped(folio));
-		error = swap_writeout(folio, plug);
+		error = swap_writeout(ctx, folio);
 		if (error != AOP_WRITEPAGE_ACTIVATE) {
 			/* folio has been unlocked */
 			return error;
@@ -1739,7 +1739,12 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
 
 int shmem_write_folio(struct folio *folio)
 {
-	return shmem_writeout(folio, NULL, NULL);
+	struct swap_io_ctx ctx = {};
+	int err;
+
+	err = shmem_writeout(&ctx, folio, NULL);
+	swap_write_submit(&ctx);
+	return err;
 }
 EXPORT_SYMBOL_GPL(shmem_write_folio);
 
diff --git a/mm/swap.h b/mm/swap.h
index 4f86ef338a60..79d66272dfd4 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -4,6 +4,7 @@
 
 #include <linux/atomic.h> /* for atomic_long_t */
 #include <linux/mm.h> /* for PAGE_SHIFT */
+
 struct mempolicy;
 struct swap_iocb;
 struct swap_memcg_table;
@@ -78,6 +79,10 @@ enum swap_cluster_flags {
 	CLUSTER_FLAG_MAX,
 };
 
+struct swap_io_ctx {
+	struct swap_iocb	*sio;
+};
+
 #ifdef CONFIG_SWAP
 #include <linux/swapops.h> /* for swp_offset */
 #include <linux/blk_types.h> /* for bio_end_io_t */
@@ -240,17 +245,11 @@ extern void __swap_cluster_free_entries(struct swap_info_struct *si,
 
 /* linux/mm/page_io.c */
 int sio_pool_init(void);
-struct swap_iocb;
-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)
-{
-	if (unlikely(plug))
-		__swap_read_unplug(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);
+void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio);
+void swap_read_submit(struct swap_io_ctx *ctx);
+void swap_write_submit(struct swap_io_ctx *ctx);
+int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio);
+void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio);
 
 /* linux/mm/swap_state.c */
 extern struct address_space swap_space __read_mostly;
@@ -317,9 +316,8 @@ void __swap_cache_replace_folio(struct swap_cluster_info *ci,
 
 void show_swap_cache_info(void);
 void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);
-struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
-		struct vm_area_struct *vma, unsigned long addr,
-		struct swap_iocb **plug);
+struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,
+		gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr);
 struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
 		struct mempolicy *mpol, pgoff_t ilx);
 struct folio *swapin_readahead(swp_entry_t entry, gfp_t flag,
@@ -335,7 +333,6 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 }
 
 #else /* CONFIG_SWAP */
-struct swap_iocb;
 static inline struct swap_cluster_info *swap_cluster_lock(
 	struct swap_info_struct *si, pgoff_t offset, bool irq)
 {
@@ -381,11 +378,11 @@ static inline void folio_put_swap(struct folio *folio, struct page *page)
 {
 }
 
-static inline void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
+static inline void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
 {
 }
 
-static inline void swap_write_unplug(struct swap_iocb *sio)
+static inline void swap_write_submit(struct swap_io_ctx *ctx)
 {
 }
 
@@ -427,8 +424,7 @@ static inline void swap_update_readahead(struct folio *folio,
 {
 }
 
-static inline int swap_writeout(struct folio *folio,
-		struct swap_iocb **swap_plug)
+static inline int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	return 0;
 }
@@ -474,7 +470,7 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
 
 #endif /* CONFIG_SWAP */
 
-int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
+int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		struct list_head *folio_list);
 
 #endif /* _MM_SWAP_H */
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 9c3a5cf99778..d8045db88057 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -633,9 +633,9 @@ void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma,
 	}
 }
 
-static struct folio *swap_cache_read_folio(swp_entry_t entry, gfp_t gfp,
-					   struct mempolicy *mpol, pgoff_t ilx,
-					   struct swap_iocb **plug, bool readahead)
+static struct folio *swap_cache_read_folio(struct swap_io_ctx *ctx,
+		swp_entry_t entry, gfp_t gfp, struct mempolicy *mpol,
+		pgoff_t ilx, bool readahead)
 {
 	struct folio *folio;
 
@@ -649,7 +649,7 @@ static struct folio *swap_cache_read_folio(swp_entry_t entry, gfp_t gfp,
 	if (IS_ERR_OR_NULL(folio))
 		return NULL;
 
-	swap_read_folio(folio, plug);
+	swap_read_folio(ctx, folio);
 	if (readahead) {
 		folio_set_readahead(folio);
 		count_vm_event(SWAP_RA);
@@ -677,6 +677,7 @@ static struct folio *swap_cache_read_folio(swp_entry_t entry, gfp_t gfp,
 struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders,
 			   struct vm_fault *vmf, struct mempolicy *mpol, pgoff_t ilx)
 {
+	struct swap_io_ctx ctx = {};
 	struct folio *folio;
 
 	do {
@@ -689,7 +690,8 @@ struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders,
 	if (IS_ERR(folio))
 		return folio;
 
-	swap_read_folio(folio, NULL);
+	swap_read_folio(&ctx, folio);
+	swap_read_submit(&ctx);
 	return folio;
 }
 
@@ -699,9 +701,8 @@ struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders,
  * A failure return means that either the page allocation failed or that
  * the swap entry is no longer in use.
  */
-struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
-		struct vm_area_struct *vma, unsigned long addr,
-		struct swap_iocb **plug)
+struct folio *read_swap_cache_async(struct swap_io_ctx *ctx, swp_entry_t entry,
+		gfp_t gfp_mask, struct vm_area_struct *vma, unsigned long addr)
 {
 	struct swap_info_struct *si;
 	struct mempolicy *mpol;
@@ -713,13 +714,24 @@ struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		return NULL;
 
 	mpol = get_vma_policy(vma, addr, 0, &ilx);
-	folio = swap_cache_read_folio(entry, gfp_mask, mpol, ilx, plug, false);
+	folio = swap_cache_read_folio(ctx, entry, gfp_mask, mpol, ilx, false);
 	mpol_cond_put(mpol);
 
 	put_swap_device(si);
 	return folio;
 }
 
+static struct folio *swap_cache_read_folio_sync(swp_entry_t entry, gfp_t gfp,
+		struct mempolicy *mpol, pgoff_t ilx)
+{
+	struct swap_io_ctx ctx = {};
+	struct folio *folio;
+
+	folio = swap_cache_read_folio(&ctx, entry, gfp, mpol, ilx, false);
+	swap_read_submit(&ctx);
+	return folio;
+}
+
 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
 				      unsigned long offset,
 				      int hits,
@@ -808,8 +820,8 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	unsigned long start_offset, end_offset;
 	unsigned long mask;
 	struct swap_info_struct *si = __swap_entry_to_info(entry);
+	struct swap_io_ctx ctx = {};
 	struct blk_plug plug;
-	struct swap_iocb *splug = NULL;
 	swp_entry_t ra_entry;
 
 	mask = swapin_nr_pages(offset) - 1;
@@ -828,18 +840,17 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	for (offset = start_offset; offset <= end_offset ; offset++) {
 		/* Ok, do the async read-ahead now */
 		ra_entry = swp_entry(swp_type(entry), offset);
-		folio = swap_cache_read_folio(ra_entry, gfp_mask, mpol, ilx,
-					      &splug, offset != entry_offset);
+		folio = swap_cache_read_folio(&ctx, ra_entry, gfp_mask, mpol,
+				ilx, offset != entry_offset);
 		if (!folio)
 			continue;
 		folio_put(folio);
 	}
 	blk_finish_plug(&plug);
-	swap_read_unplug(splug);
+	swap_read_submit(&ctx);
 	lru_add_drain();	/* Push any new pages onto the LRU now */
 skip:
-	/* The page was likely read above, so no need for plugging here */
-	return swap_cache_read_folio(entry, gfp_mask, mpol, ilx, NULL, false);
+	return swap_cache_read_folio_sync(entry, gfp_mask, mpol, ilx);
 }
 
 static int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,
@@ -899,8 +910,8 @@ static int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,
 static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 		struct mempolicy *mpol, pgoff_t targ_ilx, struct vm_fault *vmf)
 {
+	struct swap_io_ctx ctx = {};
 	struct blk_plug plug;
-	struct swap_iocb *splug = NULL;
 	struct folio *folio;
 	pte_t *pte = NULL, pentry;
 	int win;
@@ -939,8 +950,8 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 			if (!si)
 				continue;
 		}
-		folio = swap_cache_read_folio(entry, gfp_mask, mpol, ilx,
-					      &splug, addr != vmf->address);
+		folio = swap_cache_read_folio(&ctx, entry, gfp_mask, mpol, ilx,
+					      addr != vmf->address);
 		if (si)
 			put_swap_device(si);
 		if (!folio)
@@ -950,13 +961,11 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
 	if (pte)
 		pte_unmap(pte);
 	blk_finish_plug(&plug);
-	swap_read_unplug(splug);
+	swap_read_submit(&ctx);
 	lru_add_drain();
 skip:
 	/* The folio was likely read above, so no need for plugging here */
-	folio = swap_cache_read_folio(targ_entry, gfp_mask, mpol, targ_ilx,
-				      NULL, false);
-	return folio;
+	return swap_cache_read_folio_sync(targ_entry, gfp_mask, mpol, targ_ilx);
 }
 
 /**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 35c3bb15ae96..2747ee68d327 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -615,8 +615,8 @@ typedef enum {
 /*
  * pageout is called by shrink_folio_list() for each dirty folio.
  */
-static pageout_t pageout(struct folio *folio, struct address_space *mapping,
-			 struct swap_iocb **plug, struct list_head *folio_list)
+static pageout_t pageout(struct swap_io_ctx *ctx, struct address_space *mapping,
+		struct folio *folio, struct list_head *folio_list)
 {
 	int res;
 
@@ -652,9 +652,9 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping,
 	 * the split out folios get added back to folio_list.
 	 */
 	if (shmem_mapping(mapping))
-		res = shmem_writeout(folio, plug, folio_list);
+		res = shmem_writeout(ctx, folio, folio_list);
 	else
-		res = swap_writeout(folio, plug);
+		res = swap_writeout(ctx, folio);
 
 	if (res < 0)
 		handle_write_error(mapping, folio, res);
@@ -1063,7 +1063,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 	unsigned int nr_reclaimed = 0, nr_demoted = 0;
 	unsigned int pgactivate = 0;
 	bool do_demote_pass;
-	struct swap_iocb *plug = NULL;
+	struct swap_io_ctx ctx = {};
 
 	folio_batch_init(&free_folios);
 	memset(stat, 0, sizeof(*stat));
@@ -1394,7 +1394,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 			 * starts and then write it out here.
 			 */
 			try_to_unmap_flush_dirty();
-			switch (pageout(folio, mapping, &plug, folio_list)) {
+			switch (pageout(&ctx, mapping, folio, folio_list)) {
 			case PAGE_KEEP:
 				goto keep_locked;
 			case PAGE_ACTIVATE:
@@ -1584,8 +1584,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 	list_splice(&ret_folios, folio_list);
 	count_vm_events(PGACTIVATE, pgactivate);
 
-	if (plug)
-		swap_write_unplug(plug);
+	swap_write_submit(&ctx);
 	return nr_reclaimed;
 }
 
diff --git a/mm/zswap.c b/mm/zswap.c
index 761cd699e0a3..feed2557f6ed 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -992,6 +992,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	struct folio *folio;
 	struct mempolicy *mpol;
 	struct swap_info_struct *si;
+	struct swap_io_ctx ctx = {};
 	int ret = 0;
 
 	/* try to allocate swap cache folio */
@@ -1049,7 +1050,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	folio_set_reclaim(folio);
 
 	/* start writeback */
-	__swap_writepage(folio, NULL);
+	__swap_writepage(&ctx, folio);
+	swap_write_submit(&ctx);
 
 out:
 	if (ret) {
-- 
2.53.0

[PATCH 3/7] mm/swap: also use struct swap_iocb for block I/O

[Christoph Hellwig]

Block I/O benefits from batching just as much as remote file systems.
Extend struct swap_iocb to support building a bio on the fly as well,
and rewrite the block based swap code for it.  This especially benefits
submit_bio based drivers that do not have the block plugging available,
but also saves allocating extra bios for blk-mq drivers.

Add a pre-allocated bio to struct swap_iocb in a union with kiocb
used for file system based swap so that struct swap_iocb can be used
for all swap I/O, and initialize the pool for it unconditionally.

Various low-level bdev and fs functions are now replaced with a unified
can_merge/add/submit scheme.

Note that the block based swap code now uses the same memcg-based
check previously added for file system based swap as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/page_io.c  | 525 ++++++++++++++++++++++++--------------------------
 mm/swap.h     |   1 +
 mm/swapfile.c |   9 +-
 3 files changed, 253 insertions(+), 282 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index fe24a49e034c..f49e667c2b3a 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -28,54 +28,6 @@
 #include "swap.h"
 #include "swap_table.h"
 
-static void __end_swap_bio_write(struct bio *bio)
-{
-	struct folio *folio = bio_first_folio_all(bio);
-
-	if (bio->bi_status) {
-		/*
-		 * We failed to write the page out to swap-space.
-		 * Re-dirty the page in order to avoid it being reclaimed.
-		 * Also print a dire warning that things will go BAD (tm)
-		 * very quickly.
-		 *
-		 * Also clear PG_reclaim to avoid folio_rotate_reclaimable()
-		 */
-		folio_mark_dirty(folio);
-		pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
-				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
-				     (unsigned long long)bio->bi_iter.bi_sector);
-		folio_clear_reclaim(folio);
-	}
-	folio_end_writeback(folio);
-}
-
-static void end_swap_bio_write(struct bio *bio)
-{
-	__end_swap_bio_write(bio);
-	bio_put(bio);
-}
-
-static void __end_swap_bio_read(struct bio *bio)
-{
-	struct folio *folio = bio_first_folio_all(bio);
-
-	if (bio->bi_status) {
-		pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
-				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
-				     (unsigned long long)bio->bi_iter.bi_sector);
-	} else {
-		folio_mark_uptodate(folio);
-	}
-	folio_unlock(folio);
-}
-
-static void end_swap_bio_read(struct bio *bio)
-{
-	__end_swap_bio_read(bio);
-	bio_put(bio);
-}
-
 int generic_swapfile_activate(struct swap_info_struct *sis,
 				struct file *swap_file,
 				sector_t *span)
@@ -316,18 +268,35 @@ static inline void count_swpout_vm_event(struct folio *folio)
 }
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
+static struct cgroup_subsys_state *folio_memcg_blkg_css(struct folio *folio)
+{
+	return cgroup_e_css(folio_memcg(folio)->css.cgroup, &io_cgrp_subsys);
+}
+
+static bool folio_blkg_can_merge(struct folio *folio, struct folio *prev_folio)
+{
+	if (!folio_memcg_charged(folio) || !folio_memcg_charged(prev_folio))
+		return true;
+
+	rcu_read_lock();
+	if (folio_memcg_blkg_css(folio) != folio_memcg_blkg_css(prev_folio)) {
+		rcu_read_unlock();
+		return false;
+	}
+	rcu_read_unlock();
+
+	return true;
+}
+
 static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
 {
 	struct cgroup_subsys_state *css;
-	struct mem_cgroup *memcg;
 
 	if (!folio_memcg_charged(folio))
 		return;
-
 	rcu_read_lock();
-	memcg = folio_memcg(folio);
-	css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
-	if (!css || !css_tryget(css))
+	css = folio_memcg_blkg_css(folio);
+	if (css && !css_tryget(css))
 		css = NULL;
 	rcu_read_unlock();
 
@@ -336,11 +305,18 @@ static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
 		css_put(css);
 }
 #else
+static bool folio_blkg_can_merge(struct folio *folio, struct folio *prev_folio)
+{
+	return true;
+}
 #define bio_associate_blkg_from_page(bio, folio)		do { } while (0)
 #endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
 
 struct swap_iocb {
-	struct kiocb		iocb;
+	union {
+		struct kiocb	iocb;
+		struct bio	bio;
+	};
 	struct bio_vec		bvecs[SWAP_CLUSTER_MAX];
 	int			nr_bvecs;
 	int			len;
@@ -360,171 +336,70 @@ int sio_pool_init(void)
 	return 0;
 }
 
-static void sio_write_complete(struct kiocb *iocb, long ret)
+static bool swap_can_merge(struct swap_io_ctx *ctx, struct folio *folio,
+		int rw)
 {
-	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
-	struct page *page = sio->bvecs[0].bv_page;
-	int p;
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
+	struct bio_vec *last_bv = &ctx->sio->bvecs[ctx->sio->nr_bvecs - 1];
+	struct folio *prev_folio = bvec_folio(last_bv);
+	size_t prev_folio_size = folio_size(prev_folio);
 
-	if (ret != sio->len) {
-		/*
-		 * In the case of swap-over-nfs, this can be a
-		 * temporary failure if the system has limited
-		 * memory for allocating transmit buffers.
-		 * Mark the page dirty and avoid
-		 * folio_rotate_reclaimable but rate-limit the
-		 * messages.
-		 */
-		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
-				   ret, swap_dev_pos(page_swap_entry(page)));
-		for (p = 0; p < sio->nr_bvecs; p++) {
-			page = sio->bvecs[p].bv_page;
-			set_page_dirty(page);
-			ClearPageReclaim(page);
-		}
-	}
+	if (ctx->sis != sis)
+		return false;
 
-	for (p = 0; p < sio->nr_bvecs; p++)
-		end_page_writeback(sio->bvecs[p].bv_page);
+	if (sis->flags & SWP_FS_OPS) {
+		if (swap_dev_pos(folio->swap) !=
+		    swap_dev_pos(prev_folio->swap) + prev_folio_size)
+			return false;
+	} else {
+		if (swap_folio_sector(folio) !=
+		    swap_folio_sector(prev_folio) +
+		    (prev_folio_size >> SECTOR_SHIFT))
+			return false;
+		if (rw == WRITE && !folio_blkg_can_merge(folio, prev_folio))
+			return false;
+	}
 
-	mempool_free(sio, sio_pool);
+	return true;
 }
 
-static void swap_writepage_fs(struct swap_io_ctx *ctx, struct folio *folio)
+static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
 {
-	struct swap_iocb *sio = ctx->sio;
 	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);
+	struct swap_iocb *sio = ctx->sio;
 
-	count_swpout_vm_event(folio);
-	folio_start_writeback(folio);
-	folio_unlock(folio);
-	if (sio) {
-		if (sio->iocb.ki_filp != swap_file ||
-		    sio->iocb.ki_pos + sio->len != pos) {
+	if (sio && !swap_can_merge(ctx, folio, rw)) {
+		if (rw == WRITE)
 			swap_write_submit(ctx);
-			sio = NULL;
-		}
+		else
+			swap_read_submit(ctx);
+		sio = ctx->sio;
 	}
+
 	if (!sio) {
-		sio = mempool_alloc(sio_pool, GFP_NOIO);
-		init_sync_kiocb(&sio->iocb, swap_file);
-		sio->iocb.ki_complete = sio_write_complete;
-		sio->iocb.ki_pos = pos;
+		ctx->sis = sis;
+		ctx->sio = sio = mempool_alloc(sio_pool, GFP_NOIO);
 		sio->nr_bvecs = 0;
 		sio->len = 0;
 	}
 	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
 	sio->len += folio_size(folio);
-	sio->nr_bvecs += 1;
-	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
-		swap_write_submit(ctx);
-		sio = NULL;
+	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
+		if (rw == WRITE)
+			swap_write_submit(ctx);
+		else
+			swap_read_submit(ctx);
 	}
-	ctx->sio = sio;
-}
-
-static void swap_writepage_bdev_sync(struct folio *folio,
-		struct swap_info_struct *sis)
-{
-	struct bio_vec bv;
-	struct bio bio;
-
-	bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_WRITE | REQ_SWAP);
-	bio.bi_iter.bi_sector = swap_folio_sector(folio);
-	bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);
-
-	bio_associate_blkg_from_page(&bio, folio);
-	count_swpout_vm_event(folio);
-
-	folio_start_writeback(folio);
-	folio_unlock(folio);
-
-	submit_bio_wait(&bio);
-	__end_swap_bio_write(&bio);
 }
 
-static void swap_writepage_bdev_async(struct folio *folio,
-		struct swap_info_struct *sis)
+void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio)
 {
-	struct bio *bio;
-
-	bio = bio_alloc(sis->bdev, 1, REQ_OP_WRITE | REQ_SWAP, GFP_NOIO);
-	bio->bi_iter.bi_sector = swap_folio_sector(folio);
-	bio->bi_end_io = end_swap_bio_write;
-	bio_add_folio_nofail(bio, folio, folio_size(folio), 0);
+	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
 
-	bio_associate_blkg_from_page(bio, folio);
 	count_swpout_vm_event(folio);
 	folio_start_writeback(folio);
 	folio_unlock(folio);
-	submit_bio(bio);
-}
-
-void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio)
-{
-	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(ctx, folio);
-	/*
-	 * ->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_submit(struct swap_io_ctx *ctx)
-{
-	struct swap_iocb *sio = ctx->sio;
-	struct iov_iter from;
-	int ret;
-
-	if (!sio)
-		return;
-
-	iov_iter_bvec(&from, ITER_SOURCE, sio->bvecs, sio->nr_bvecs, sio->len);
-	ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &from);
-	if (ret != -EIOCBQUEUED)
-		sio_write_complete(&sio->iocb, ret);
-	ctx->sio = NULL;
-}
-
-static void sio_read_complete(struct kiocb *iocb, long ret)
-{
-	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
-	int p;
-
-	if (ret == sio->len) {
-		for (p = 0; p < sio->nr_bvecs; p++) {
-			struct folio *folio = bvec_folio(&sio->bvecs[p]);
-
-			count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
-			count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
-			folio_mark_uptodate(folio);
-			folio_unlock(folio);
-		}
-		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
-	} else {
-		for (p = 0; p < sio->nr_bvecs; p++) {
-			struct folio *folio = bvec_folio(&sio->bvecs[p]);
-
-			folio_unlock(folio);
-		}
-		pr_alert_ratelimited("Read-error on swap-device\n");
-	}
-	mempool_free(sio, sio_pool);
+	swap_add_folio(ctx, folio, WRITE);
 }
 
 /*
@@ -590,74 +465,6 @@ static bool swap_read_folio_zeromap(struct folio *folio)
 	return true;
 }
 
-static void swap_read_folio_fs(struct swap_io_ctx *ctx, struct folio *folio)
-{
-	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
-	struct swap_iocb *sio = ctx->sio;
-	loff_t pos = swap_dev_pos(folio->swap);
-
-	if (sio) {
-		if (sio->iocb.ki_filp != sis->swap_file ||
-		    sio->iocb.ki_pos + sio->len != pos) {
-			swap_read_submit(ctx);
-			sio = NULL;
-		}
-	}
-	if (!sio) {
-		sio = mempool_alloc(sio_pool, GFP_KERNEL);
-		init_sync_kiocb(&sio->iocb, sis->swap_file);
-		sio->iocb.ki_pos = pos;
-		sio->iocb.ki_complete = sio_read_complete;
-		sio->nr_bvecs = 0;
-		sio->len = 0;
-	}
-	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
-	sio->len += folio_size(folio);
-	sio->nr_bvecs += 1;
-	if (sio->nr_bvecs == ARRAY_SIZE(sio->bvecs)) {
-		swap_read_submit(ctx);
-		sio = NULL;
-	}
-	ctx->sio = sio;
-}
-
-static void swap_read_folio_bdev_sync(struct folio *folio,
-		struct swap_info_struct *sis)
-{
-	struct bio_vec bv;
-	struct bio bio;
-
-	bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_READ);
-	bio.bi_iter.bi_sector = swap_folio_sector(folio);
-	bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);
-	/*
-	 * Keep this task valid during swap readpage because the oom killer may
-	 * attempt to access it in the page fault retry time check.
-	 */
-	get_task_struct(current);
-	count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
-	count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
-	count_vm_events(PSWPIN, folio_nr_pages(folio));
-	submit_bio_wait(&bio);
-	__end_swap_bio_read(&bio);
-	put_task_struct(current);
-}
-
-static void swap_read_folio_bdev_async(struct folio *folio,
-		struct swap_info_struct *sis)
-{
-	struct bio *bio;
-
-	bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
-	bio->bi_iter.bi_sector = swap_folio_sector(folio);
-	bio->bi_end_io = end_swap_bio_read;
-	bio_add_folio_nofail(bio, folio, folio_size(folio), 0);
-	count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
-	count_memcg_folio_events(folio, PSWPIN, folio_nr_pages(folio));
-	count_vm_events(PSWPIN, folio_nr_pages(folio));
-	submit_bio(bio);
-}
-
 void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
@@ -691,14 +498,7 @@ void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
 
 	/* 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(ctx, folio);
-	} else if (synchronous) {
-		swap_read_folio_bdev_sync(folio, sis);
-	} else {
-		swap_read_folio_bdev_async(folio, sis);
-	}
+	swap_add_folio(ctx, folio, READ);
 
 finish:
 	if (workingset) {
@@ -708,18 +508,189 @@ void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
 	delayacct_swapin_end();
 }
 
-void swap_read_submit(struct swap_io_ctx *ctx)
+static void swap_write_end(struct swap_iocb *sio, bool failed)
+{
+	int p;
+
+	for (p = 0; p < sio->nr_bvecs; p++) {
+		struct page *page = sio->bvecs[p].bv_page;
+
+		if (failed) {
+			set_page_dirty(page);
+			ClearPageReclaim(page);
+		}
+		end_page_writeback(page);
+	}
+	mempool_free(sio, sio_pool);
+}
+
+static void swap_fs_write_complete(struct kiocb *iocb, long ret)
+{
+	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+	bool failed = ret != sio->len;
+
+	if (failed) {
+		struct page *page = sio->bvecs[0].bv_page;
+
+		/*
+		 * In the case of swap-over-nfs, this can be a temporary failure
+		 * if the system has limited memory for allocating transmit
+		 * buffers.  Mark the page dirty and avoid
+		 * folio_rotate_reclaimable but rate-limit the messages.
+		 */
+		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
+				   ret, swap_dev_pos(page_swap_entry(page)));
+	}
+
+	swap_write_end(sio, failed);
+}
+
+static void end_swap_bio_write(struct bio *bio)
+{
+	struct swap_iocb *sio = container_of(bio, struct swap_iocb, bio);
+	bool failed = !!bio->bi_status;
+
+	if (failed)
+		pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
+				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+				     (unsigned long long)bio->bi_iter.bi_sector);
+	bio_uninit(bio);
+	swap_write_end(sio, failed);
+}
+
+static void swap_read_end(struct swap_iocb *sio, bool failed)
+{
+	int p;
+
+	for (p = 0; p < sio->nr_bvecs; p++) {
+		struct folio *folio = bvec_folio(&sio->bvecs[p]);
+
+		if (!failed) {
+			count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
+			count_memcg_folio_events(folio, PSWPIN,
+					folio_nr_pages(folio));
+			folio_mark_uptodate(folio);
+		}
+		folio_unlock(folio);
+	}
+
+	if (!failed)
+		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
+
+	mempool_free(sio, sio_pool);
+}
+
+static void swap_fs_read_complete(struct kiocb *iocb, long ret)
+{
+	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+	bool failed = ret != sio->len;
+
+	if (failed)
+		pr_alert_ratelimited("Read-error on swap-device\n");
+	swap_read_end(sio, failed);
+}
+
+static void swap_bio_read_end_io(struct bio *bio)
+{
+	struct swap_iocb *sio = container_of(bio, struct swap_iocb, bio);
+	bool failed = !!bio->bi_status;
+
+	if (failed)
+		pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
+				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+				     (unsigned long long)bio->bi_iter.bi_sector);
+	bio_uninit(bio);
+	swap_read_end(sio, failed);
+}
+
+static void swap_bdev_submit_write(struct swap_io_ctx *ctx)
 {
 	struct swap_iocb *sio = ctx->sio;
-	struct iov_iter from;
+	struct bio *bio = &sio->bio;
+
+	bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs),
+			REQ_OP_WRITE | REQ_SWAP);
+	bio->bi_iter.bi_size = sio->len;
+	bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio));
+	bio_associate_blkg_from_page(bio, bio_first_folio_all(bio));
+
+	if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) {
+		submit_bio_wait(bio);
+		end_swap_bio_write(bio);
+	} else {
+		bio->bi_end_io = end_swap_bio_write;
+		submit_bio(bio);
+	}
+}
+
+static void swap_bdev_submit_read(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct bio *bio = &sio->bio;
+
+	bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs),
+			REQ_OP_READ);
+	bio->bi_iter.bi_size = sio->len;
+	bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio));
+
+	if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) {
+		/*
+		 * Keep this task valid during swap readpage because the oom
+		 * killer may attempt to access it in the page fault retry
+		 * time check.
+		 */
+		get_task_struct(current);
+		submit_bio_wait(bio);
+		swap_bio_read_end_io(bio);
+		put_task_struct(current);
+	} else {
+		bio->bi_end_io = swap_bio_read_end_io;
+		submit_bio(bio);
+	}
+}
+
+static void swap_fs_submit(struct swap_io_ctx *ctx, int rw)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct iov_iter iter;
 	int ret;
 
-	if (!sio)
-		return;
+	init_sync_kiocb(&sio->iocb, ctx->sis->swap_file);
+	sio->iocb.ki_pos = swap_dev_pos(bvec_folio(&sio->bvecs[0])->swap);
+	if (rw == WRITE)
+		sio->iocb.ki_complete = swap_fs_write_complete;
+	else
+		sio->iocb.ki_complete = swap_fs_read_complete;
 
-	iov_iter_bvec(&from, ITER_DEST, sio->bvecs, sio->nr_bvecs, sio->len);
-	ret = sio->iocb.ki_filp->f_mapping->a_ops->swap_rw(&sio->iocb, &from);
+	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_read_complete(&sio->iocb, ret);
+		sio->iocb.ki_complete(&sio->iocb, ret);
+}
+
+void swap_write_submit(struct swap_io_ctx *ctx)
+{
+	if (!ctx->sio)
+		return;
+
+	if (ctx->sis->flags & SWP_FS_OPS)
+		swap_fs_submit(ctx, WRITE);
+	else
+		swap_bdev_submit_write(ctx);
+	ctx->sio = NULL;
+	ctx->sis = NULL;
+}
+
+void swap_read_submit(struct swap_io_ctx *ctx)
+{
+	if (!ctx->sio)
+		return;
+
+	if (ctx->sis->flags & SWP_FS_OPS)
+		swap_fs_submit(ctx, READ);
+	else
+		swap_bdev_submit_read(ctx);
 	ctx->sio = NULL;
+	ctx->sis = NULL;
 }
diff --git a/mm/swap.h b/mm/swap.h
index 79d66272dfd4..b6ba80c2afb0 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -81,6 +81,7 @@ enum swap_cluster_flags {
 
 struct swap_io_ctx {
 	struct swap_iocb	*sio;
+	struct swap_info_struct	*sis;
 };
 
 #ifdef CONFIG_SWAP
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 78b49b0658ad..1887df22bd1e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2941,6 +2941,10 @@ static int setup_swap_extents(struct swap_info_struct *sis,
 	struct inode *inode = mapping->host;
 	int ret;
 
+	ret = sio_pool_init();
+	if (ret)
+		return ret;
+
 	if (S_ISBLK(inode->i_mode)) {
 		ret = add_swap_extent(sis, 0, sis->max, 0);
 		*span = sis->pages;
@@ -2952,11 +2956,6 @@ static int setup_swap_extents(struct swap_info_struct *sis,
 		if (ret < 0)
 			return ret;
 		sis->flags |= SWP_ACTIVATED;
-		if ((sis->flags & SWP_FS_OPS) &&
-		    sio_pool_init() != 0) {
-			destroy_swap_extents(sis, swap_file);
-			return -ENOMEM;
-		}
 		return ret;
 	}
 
-- 
2.53.0

[PATCH 4/7] mm/swap: remove count_swpout_vm_event

[Christoph Hellwig]

There is only one caller left, so merge it into that.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
---
 mm/page_io.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index f49e667c2b3a..6009f6991b73 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -254,19 +254,6 @@ int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio)
 	return ret;
 }
 
-static inline void count_swpout_vm_event(struct folio *folio)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (unlikely(folio_test_pmd_mappable(folio))) {
-		count_memcg_folio_events(folio, THP_SWPOUT, 1);
-		count_vm_event(THP_SWPOUT);
-	}
-#endif
-	count_mthp_stat(folio_order(folio), MTHP_STAT_SWPOUT);
-	count_memcg_folio_events(folio, PSWPOUT, folio_nr_pages(folio));
-	count_vm_events(PSWPOUT, folio_nr_pages(folio));
-}
-
 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
 static struct cgroup_subsys_state *folio_memcg_blkg_css(struct folio *folio)
 {
@@ -396,7 +383,16 @@ void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio)
 {
 	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
 
-	count_swpout_vm_event(folio);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (unlikely(folio_test_pmd_mappable(folio))) {
+		count_memcg_folio_events(folio, THP_SWPOUT, 1);
+		count_vm_event(THP_SWPOUT);
+	}
+#endif
+	count_mthp_stat(folio_order(folio), MTHP_STAT_SWPOUT);
+	count_memcg_folio_events(folio, PSWPOUT, folio_nr_pages(folio));
+	count_vm_events(PSWPOUT, folio_nr_pages(folio));
+
 	folio_start_writeback(folio);
 	folio_unlock(folio);
 	swap_add_folio(ctx, folio, WRITE);
-- 
2.53.0

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

[Christoph Hellwig]

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

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

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

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

[PATCH 6/7] mm/swap: remove SWP_FS_OPS

[Christoph Hellwig]

Provide a swap_fs_activate helper that directly sets up swap_fs_ops,
and a flag in struct swap_ops to indicate of NOFS swapping is allowed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 Documentation/filesystems/locking.rst |  5 +++--
 Documentation/filesystems/vfs.rst     |  4 ++--
 fs/nfs/file.c                         |  4 +---
 fs/smb/client/file.c                  |  4 +---
 include/linux/swap.h                  |  6 +++++-
 mm/page_io.c                          | 10 +++++++++-
 mm/swap.h                             | 22 ++++++++++------------
 mm/swapfile.c                         |  2 --
 mm/vmscan.c                           | 15 +++++++--------
 9 files changed, 38 insertions(+), 34 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 08d01bc62c31..1a50d41a39a1 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -355,13 +355,14 @@ 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 set SWP_FS_OPS, otherwise IO will be submitted
+->swap_rw(), 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 SWP_FS_OPS was set by ->swap_activate().
+->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 7c753148af88..e7677423a20f 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -977,7 +977,7 @@ 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 set SWP_FS_OPS, otherwise IO will
+	through ->swap_rw(), it should call swap_fs_activate, otherwise IO will
 	be submitted directly to the block device ``sis->bdev``.
 
 ``swap_deactivate``
@@ -985,7 +985,7 @@ cache in your filesystem.  The following members are defined:
 	successful.
 
 ``swap_rw``
-	Called to read or write swap pages when SWP_FS_OPS is set.
+	Called to read or write swap pages when swap_fs_activate was called.
 
 The File Object
 ===============
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index a0d8f1c1cf10..851d93a09988 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -597,7 +597,7 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 	ret = rpc_clnt_swap_activate(clnt);
 	if (ret)
 		return ret;
-	ret = add_swap_extent(sis, 0, sis->max, 0);
+	ret = swap_fs_activate(sis);
 	if (ret < 0) {
 		rpc_clnt_swap_deactivate(clnt);
 		return ret;
@@ -607,8 +607,6 @@ static int nfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 
 	if (cl->rpc_ops->enable_swap)
 		cl->rpc_ops->enable_swap(inode);
-
-	sis->flags |= SWP_FS_OPS;
 	return ret;
 }
 
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index 5a25635bc62a..4b1bc16b8f3f 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -3387,9 +3387,7 @@ 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
 	 */
-
-	sis->flags |= SWP_FS_OPS;
-	return add_swap_extent(sis, 0, sis->max, 0);
+	return swap_fs_activate(sis);
 }
 
 static void cifs_swap_deactivate(struct file *file)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 74ceb7a88fd5..bb53601e05b3 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -208,7 +208,6 @@ enum {
 	SWP_SOLIDSTATE	= (1 << 4),	/* blkdev seeks are cheap */
 	SWP_BLKDEV	= (1 << 6),	/* its a block device */
 	SWP_ACTIVATED	= (1 << 7),	/* set after swap_activate success */
-	SWP_FS_OPS	= (1 << 8),	/* swapfile operations go through fs */
 	SWP_AREA_DISCARD = (1 << 9),	/* single-time swap area discards */
 	SWP_PAGE_DISCARD = (1 << 10),	/* freed swap page-cluster discards */
 	SWP_STABLE_WRITES = (1 << 11),	/* no overwrite PG_writeback pages */
@@ -404,6 +403,7 @@ 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 *,
@@ -530,6 +530,10 @@ 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/mm/page_io.c b/mm/page_io.c
index d2b11db1a57f..1e29b36cec07 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -685,12 +685,20 @@ static bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio,
 		swap_dev_pos(prev_folio->swap) + prev_folio_size;
 }
 
-const struct swap_ops swap_fs_ops = {
+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)
+{
+	sis->ops = &swap_fs_ops;
+	return add_swap_extent(sis, 0, sis->max, 0);
+}
+EXPORT_SYMBOL_GPL(swap_fs_activate);
+
 void swap_write_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
diff --git a/mm/swap.h b/mm/swap.h
index 5119feff0e93..0ff2f82eced3 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -84,7 +84,17 @@ struct swap_io_ctx {
 	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);
@@ -335,11 +345,6 @@ struct folio *swapin_sync(swp_entry_t entry, gfp_t flag, unsigned long orders,
 void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma,
 			   unsigned long addr);
 
-static inline unsigned int folio_swap_flags(struct folio *folio)
-{
-	return __swap_entry_to_info(folio->swap)->flags;
-}
-
 #else /* CONFIG_SWAP */
 static inline struct swap_cluster_info *swap_cluster_lock(
 	struct swap_info_struct *si, pgoff_t offset, bool irq)
@@ -470,16 +475,9 @@ static inline void __swap_cache_replace_folio(struct swap_cluster_info *ci,
 		struct folio *old, struct folio *new)
 {
 }
-
-static inline unsigned int folio_swap_flags(struct folio *folio)
-{
-	return 0;
-}
-
 #endif /* CONFIG_SWAP */
 
 extern const struct swap_ops swap_bdev_ops;
-extern const struct swap_ops swap_fs_ops;
 
 int shmem_writeout(struct swap_io_ctx *ctx, struct folio *folio,
 		struct list_head *folio_list);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index b291510813a6..b0b843372f67 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2957,8 +2957,6 @@ static int setup_swap_extents(struct swap_info_struct *sis,
 		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
 		if (ret < 0)
 			return ret;
-		if (sis->flags & SWP_FS_OPS)
-			sis->ops = &swap_fs_ops;
 		sis->flags |= SWP_ACTIVATED;
 		return ret;
 	}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2747ee68d327..ef280a24454f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1037,16 +1037,15 @@ static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)
 {
 	if (gfp_mask & __GFP_FS)
 		return true;
-	if (!folio_test_swapcache(folio) || !(gfp_mask & __GFP_IO))
-		return false;
 	/*
-	 * We can "enter_fs" for swap-cache with only __GFP_IO
-	 * providing this isn't SWP_FS_OPS.
-	 * ->flags can be updated non-atomically,
-	 * but that will never affect SWP_FS_OPS, so the data_race
-	 * is safe.
+	 * We can "enter_fs" for swap-cache with only __GFP_IO unless backed by
+	 * a swapfile that requires GFP_NOFS I/O.
 	 */
-	return !data_race(folio_swap_flags(folio) & SWP_FS_OPS);
+	if (folio_test_swapcache(folio) && (gfp_mask & __GFP_IO) &&
+	    !(__swap_entry_to_info(folio->swap)->ops->flags &
+			SWAP_OPS_F_REQUIRE_NOFS))
+		return true;
+	return false;
 }
 
 /*
-- 
2.53.0

[PATCH 7/7] mm/vmstat: add NRSWP{IN,OUT} counters

[Christoph Hellwig]

Count how many swap I/Os we cause.  Due to batching this can be different
than the current counter number of pages written/read, and tracking this
information is useful to see how efficient the batching is.

The counters are added at the end of enum vm_event_item and the
vmstat_text array under the assumption that the order of fields in
/proc/vmstat is an ABI.  If that is not the case, they could be grouped
with the other swap counters.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/vm_event_item.h | 4 ++++
 mm/page_io.c                  | 2 ++
 mm/vmstat.c                   | 6 +++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 03fe95f5a020..2628ccda076a 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -175,6 +175,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		KSTACK_REST,
 #endif
 #endif /* CONFIG_DEBUG_STACK_USAGE */
+#ifdef CONFIG_SWAP
+		NRSWPIN,
+		NRSWPOUT,
+#endif /* CONFIG_SWAP */
 		NR_VM_EVENT_ITEMS
 };
 
diff --git a/mm/page_io.c b/mm/page_io.c
index 1e29b36cec07..c7681dbcfc76 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -703,6 +703,7 @@ void swap_write_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
+	count_vm_events(NRSWPOUT, 1);
 	ctx->sis->ops->submit_write(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
@@ -712,6 +713,7 @@ void swap_read_submit(struct swap_io_ctx *ctx)
 {
 	if (!ctx->sio)
 		return;
+	count_vm_events(NRSWPIN, 1);
 	ctx->sis->ops->submit_read(ctx);
 	ctx->sio = NULL;
 	ctx->sis = NULL;
diff --git a/mm/vmstat.c b/mm/vmstat.c
index f534972f517d..9559f3c95735 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1488,7 +1488,11 @@ const char * const vmstat_text[] = {
 #if THREAD_SIZE > 65536
 	[I(KSTACK_REST)]			= "kstack_rest",
 #endif
-#endif
+#endif /* CONFIG_DEBUG_STACK_USAGE */
+#ifdef CONFIG_SWAP
+	[I(NRSWPIN)]				= "nrswpin",
+	[I(NRSWPOUT)]				= "nrswpout",
+#endif /* CONFIG_SWAP */
 #undef I
 #endif /* CONFIG_VM_EVENT_COUNTERS */
 };
-- 
2.53.0

Re: better block swap batching and a different take on swap_ops v3

[Andrew Morton]

On Mon,  6 Jul 2026 15:21:52 +0200 Christoph Hellwig <hch@lst.de> wrote:

> this series makes use of the swap_iocb for block as well so that it
> doesn't do inefficient single-bio I/O, and then rebases the swap_ops from
> Baoquan on top of the now very different method structure.
> 
> When running doing kernels builds, which is a workload that doesn't
> really do much THP anonymous memory it still gets 2x clustering for
> writeout and 1.2x for reading back swap in.  The overall times do
> not actually change, though.

Thanks.

AI review might have found some pre-existing bugs in 
drivers/gpu/drm/i915/gem/i915_gem_shmem.c
drivers/gpu/drm/ttm/ttm_backup.c

	https://sashiko.dev/#/patchset/20260706132206.935272-1-hch@lst.de

Re: [PATCH 1/7] shmem: provide a shmem_write_folio wrapper

[Baolin Wang]

On 7/6/26 9:21 PM, Christoph Hellwig wrote:
> Provide a wrapper for the shmem abuses in drm to prepare for swap I/O
> refactoring by keeping swap_iocb handling entirely contained in mm/.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Baoquan He <baoquan.he@linux.dev>
> Reviewed-by: Nhat Pham <nphamcs@gmail.com>
> Acked-by: Chris Li <chrisl@kernel.org>
> ---

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>

Re: better block swap batching and a different take on swap_ops v3

[Christoph Hellwig]

On Mon, Jul 06, 2026 at 10:21:18AM -0700, Andrew Morton wrote:
> On Mon,  6 Jul 2026 15:21:52 +0200 Christoph Hellwig <hch@lst.de> wrote:
> 
> > this series makes use of the swap_iocb for block as well so that it
> > doesn't do inefficient single-bio I/O, and then rebases the swap_ops from
> > Baoquan on top of the now very different method structure.
> > 
> > When running doing kernels builds, which is a workload that doesn't
> > really do much THP anonymous memory it still gets 2x clustering for
> > writeout and 1.2x for reading back swap in.  The overall times do
> > not actually change, though.
> 
> Thanks.
> 
> AI review might have found some pre-existing bugs in 
> drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> drivers/gpu/drm/ttm/ttm_backup.c
> 
> 	https://sashiko.dev/#/patchset/20260706132206.935272-1-hch@lst.de

I know, but it's not really relevant to this series, and the drm
folks keep ignoring it.  See also:

https://lore.kernel.org/all/20260609085534.GA12980@lst.de/