[PATCH 0/2] btrfs: rename btrfs_subpage to btrfs_folio_state

[PATCH 0/2] btrfs: rename btrfs_subpage to btrfs_folio_state

[Qu Wenruo]

This migration is mostly to align the naming to iomap, so btrfs_subpage
is renamed to btrfs_folio_state.

But before the rename, explain why btrfs needs the following extra
sub-bitmaps in the first patch.

Qu Wenruo (2):
  btrfs: add comments on the extra btrfs specific subpage bitmaps
  btrfs: rename btrfs_subpage structure

 fs/btrfs/extent_io.c |  29 +++---
 fs/btrfs/inode.c     |   8 +-
 fs/btrfs/subpage.c   | 239 +++++++++++++++++++++----------------------
 fs/btrfs/subpage.h   |  46 +++++++--
 4 files changed, 172 insertions(+), 150 deletions(-)

-- 
2.49.0

[PATCH 1/2] btrfs: add comments on the extra btrfs specific subpage bitmaps

[Qu Wenruo]

Unlike the iomap_folio_state structure, the btrfs_subpage structure has a
lot of extra sub-bitmaps, namingly:

- writeback sub-bitmap
- locked sub-bitmap
  iomap_folio_state uses an atomic for writeback tracking, meanwhile has
  no per-block locked tracking.

  This is because iomap always lock a single folio, and submit dirty
  blocks with that folio locked.

  But btrfs has async delalloc ranges (for compression), which are queued
  with their range locked, until the compression is done, then mark the
  involved range writeback and unlocked.

  This means a range can be unlocked and marked writeback at seemingly
  random timing, thus needs the extra tracking.

  This needs a huge rework on the lifespan of async delalloc range
  before we can remove/simplify those two sub-bitmaps.

- ordered sub-bitmap
- checked sub-bitmap
  These are for COW-fixup, but as I mentioned in the past, the COW-fixup
  is not really needed and those two flags are already marked
  deprecated, and will be removed in the near-future after comprehensive
  tests.

Add related comments to indicate we're actively trying to align the
sub-bitmaps to the iomap ones.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/subpage.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 3042c5ea840a..52546e0e97ce 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -33,8 +33,22 @@ enum {
 	btrfs_bitmap_nr_uptodate = 0,
 	btrfs_bitmap_nr_dirty,
 	btrfs_bitmap_nr_writeback,
+	/*
+	 * The ordered and checked flags are for COW fixup, already marked
+	 * deprecated, and will be removed eventually.
+	 */
 	btrfs_bitmap_nr_ordered,
 	btrfs_bitmap_nr_checked,
+
+	/*
+	 * The locked bit is for async delalloc range (compression), currently
+	 * async extent is queued with the range locked, until the compression
+	 * is done.
+	 * So an async extent can unlock the range at any random timing.
+	 *
+	 * This will need a rework on the async extent lifespan (mark writeback
+	 * and do compression) before deprecating this flag.
+	 */
 	btrfs_bitmap_nr_locked,
 	btrfs_bitmap_nr_max
 };
-- 
2.49.0

[PATCH 2/2] btrfs: rename btrfs_subpage structure

[Qu Wenruo]

With the incoming large data folios support, the structure name
btrfs_subpage is no longer correct, as for we can have multiple blocks
inside a large folio, and the block size is still page size.

So to follow the schema of iomap, rename btrfs_subpage to
btrfs_folio_state, along with involved enums.

There are still exported functions with "btrfs_subpage_" prefix, and I
believe for metadata the name "subpage" will stay forever as we will
never allocate a folio larger than nodesize anyway.

The full cleanup of the word "subpage" will happen in much smaller steps
in the future.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c |  29 +++---
 fs/btrfs/inode.c     |   8 +-
 fs/btrfs/subpage.c   | 239 +++++++++++++++++++++----------------------
 fs/btrfs/subpage.h   |  32 ++++--
 4 files changed, 158 insertions(+), 150 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 849199768664..c562b589876e 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -782,7 +782,7 @@ static void submit_extent_folio(struct btrfs_bio_ctrl *bio_ctrl,
 
 static int attach_extent_buffer_folio(struct extent_buffer *eb,
 				      struct folio *folio,
-				      struct btrfs_subpage *prealloc)
+				      struct btrfs_folio_state *prealloc)
 {
 	struct btrfs_fs_info *fs_info = eb->fs_info;
 	int ret = 0;
@@ -806,7 +806,7 @@ static int attach_extent_buffer_folio(struct extent_buffer *eb,
 
 	/* Already mapped, just free prealloc */
 	if (folio_test_private(folio)) {
-		btrfs_free_subpage(prealloc);
+		btrfs_free_folio_state(prealloc);
 		return 0;
 	}
 
@@ -815,7 +815,7 @@ static int attach_extent_buffer_folio(struct extent_buffer *eb,
 		folio_attach_private(folio, prealloc);
 	else
 		/* Do new allocation to attach subpage */
-		ret = btrfs_attach_subpage(fs_info, folio, BTRFS_SUBPAGE_METADATA);
+		ret = btrfs_attach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);
 	return ret;
 }
 
@@ -831,7 +831,7 @@ int set_folio_extent_mapped(struct folio *folio)
 	fs_info = folio_to_fs_info(folio);
 
 	if (btrfs_is_subpage(fs_info, folio))
-		return btrfs_attach_subpage(fs_info, folio, BTRFS_SUBPAGE_DATA);
+		return btrfs_attach_folio_state(fs_info, folio, BTRFS_SUBPAGE_DATA);
 
 	folio_attach_private(folio, (void *)EXTENT_FOLIO_PRIVATE);
 	return 0;
@@ -848,7 +848,7 @@ void clear_folio_extent_mapped(struct folio *folio)
 
 	fs_info = folio_to_fs_info(folio);
 	if (btrfs_is_subpage(fs_info, folio))
-		return btrfs_detach_subpage(fs_info, folio, BTRFS_SUBPAGE_DATA);
+		return btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_DATA);
 
 	folio_detach_private(folio);
 }
@@ -2731,13 +2731,13 @@ static int extent_buffer_under_io(const struct extent_buffer *eb)
 
 static bool folio_range_has_eb(struct folio *folio)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	lockdep_assert_held(&folio->mapping->i_private_lock);
 
 	if (folio_test_private(folio)) {
-		subpage = folio_get_private(folio);
-		if (atomic_read(&subpage->eb_refs))
+		bfs = folio_get_private(folio);
+		if (atomic_read(&bfs->eb_refs))
 			return true;
 	}
 	return false;
@@ -2787,7 +2787,7 @@ static void detach_extent_buffer_folio(const struct extent_buffer *eb, struct fo
 	 * attached to one dummy eb, no sharing.
 	 */
 	if (!mapped) {
-		btrfs_detach_subpage(fs_info, folio, BTRFS_SUBPAGE_METADATA);
+		btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);
 		return;
 	}
 
@@ -2798,7 +2798,7 @@ static void detach_extent_buffer_folio(const struct extent_buffer *eb, struct fo
 	 * page range and no unfinished IO.
 	 */
 	if (!folio_range_has_eb(folio))
-		btrfs_detach_subpage(fs_info, folio, BTRFS_SUBPAGE_METADATA);
+		btrfs_detach_folio_state(fs_info, folio, BTRFS_SUBPAGE_METADATA);
 
 	spin_unlock(&mapping->i_private_lock);
 }
@@ -3141,7 +3141,7 @@ static bool check_eb_alignment(struct btrfs_fs_info *fs_info, u64 start)
  * The caller needs to free the existing folios and retry using the same order.
  */
 static int attach_eb_folio_to_filemap(struct extent_buffer *eb, int i,
-				      struct btrfs_subpage *prealloc,
+				      struct btrfs_folio_state *prealloc,
 				      struct extent_buffer **found_eb_ret)
 {
 
@@ -3224,7 +3224,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	int attached = 0;
 	struct extent_buffer *eb;
 	struct extent_buffer *existing_eb = NULL;
-	struct btrfs_subpage *prealloc = NULL;
+	struct btrfs_folio_state *prealloc = NULL;
 	u64 lockdep_owner = owner_root;
 	bool page_contig = true;
 	int uptodate = 1;
@@ -3269,7 +3269,8 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	 * manually if we exit earlier.
 	 */
 	if (btrfs_meta_is_subpage(fs_info)) {
-		prealloc = btrfs_alloc_subpage(fs_info, PAGE_SIZE, BTRFS_SUBPAGE_METADATA);
+		prealloc = btrfs_alloc_folio_state(fs_info, PAGE_SIZE,
+						   BTRFS_SUBPAGE_METADATA);
 		if (IS_ERR(prealloc)) {
 			ret = PTR_ERR(prealloc);
 			goto out;
@@ -3280,7 +3281,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	/* Allocate all pages first. */
 	ret = alloc_eb_folio_array(eb, true);
 	if (ret < 0) {
-		btrfs_free_subpage(prealloc);
+		btrfs_free_folio_state(prealloc);
 		goto out;
 	}
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7074f975c033..a1516615c335 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7368,13 +7368,13 @@ struct extent_map *btrfs_create_io_em(struct btrfs_inode *inode, u64 start,
 static void wait_subpage_spinlock(struct folio *folio)
 {
 	struct btrfs_fs_info *fs_info = folio_to_fs_info(folio);
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	if (!btrfs_is_subpage(fs_info, folio))
 		return;
 
 	ASSERT(folio_test_private(folio) && folio_get_private(folio));
-	subpage = folio_get_private(folio);
+	bfs = folio_get_private(folio);
 
 	/*
 	 * This may look insane as we just acquire the spinlock and release it,
@@ -7387,8 +7387,8 @@ static void wait_subpage_spinlock(struct folio *folio)
 	 * Here we just acquire the spinlock so that all existing callers
 	 * should exit and we're safe to release/invalidate the page.
 	 */
-	spin_lock_irq(&subpage->lock);
-	spin_unlock_irq(&subpage->lock);
+	spin_lock_irq(&bfs->lock);
+	spin_unlock_irq(&bfs->lock);
 }
 
 static int btrfs_launder_folio(struct folio *folio)
diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index d4f019233493..9b63a4d1c989 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -49,7 +49,7 @@
  * Implementation:
  *
  * - Common
- *   Both metadata and data will use a new structure, btrfs_subpage, to
+ *   Both metadata and data will use a new structure, btrfs_folio_state, to
  *   record the status of each sector inside a page.  This provides the extra
  *   granularity needed.
  *
@@ -63,10 +63,10 @@
  *   This means a slightly higher tree locking latency.
  */
 
-int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
-			 struct folio *folio, enum btrfs_subpage_type type)
+int btrfs_attach_folio_state(const struct btrfs_fs_info *fs_info,
+			     struct folio *folio, enum btrfs_folio_type type)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	/* For metadata we don't support large folio yet. */
 	if (type == BTRFS_SUBPAGE_METADATA)
@@ -87,18 +87,18 @@ int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
 	if (type == BTRFS_SUBPAGE_DATA && !btrfs_is_subpage(fs_info, folio))
 		return 0;
 
-	subpage = btrfs_alloc_subpage(fs_info, folio_size(folio), type);
-	if (IS_ERR(subpage))
-		return  PTR_ERR(subpage);
+	bfs = btrfs_alloc_folio_state(fs_info, folio_size(folio), type);
+	if (IS_ERR(bfs))
+		return PTR_ERR(bfs);
 
-	folio_attach_private(folio, subpage);
+	folio_attach_private(folio, bfs);
 	return 0;
 }
 
-void btrfs_detach_subpage(const struct btrfs_fs_info *fs_info, struct folio *folio,
-			  enum btrfs_subpage_type type)
+void btrfs_detach_folio_state(const struct btrfs_fs_info *fs_info, struct folio *folio,
+			      enum btrfs_folio_type type)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	/* Either not subpage, or the folio already has private attached. */
 	if (!folio_test_private(folio))
@@ -108,15 +108,15 @@ void btrfs_detach_subpage(const struct btrfs_fs_info *fs_info, struct folio *fol
 	if (type == BTRFS_SUBPAGE_DATA && !btrfs_is_subpage(fs_info, folio))
 		return;
 
-	subpage = folio_detach_private(folio);
-	ASSERT(subpage);
-	btrfs_free_subpage(subpage);
+	bfs = folio_detach_private(folio);
+	ASSERT(bfs);
+	btrfs_free_folio_state(bfs);
 }
 
-struct btrfs_subpage *btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
-				size_t fsize, enum btrfs_subpage_type type)
+struct btrfs_folio_state *btrfs_alloc_folio_state(const struct btrfs_fs_info *fs_info,
+						  size_t fsize, enum btrfs_folio_type type)
 {
-	struct btrfs_subpage *ret;
+	struct btrfs_folio_state *ret;
 	unsigned int real_size;
 
 	ASSERT(fs_info->sectorsize < fsize);
@@ -136,11 +136,6 @@ struct btrfs_subpage *btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
-void btrfs_free_subpage(struct btrfs_subpage *subpage)
-{
-	kfree(subpage);
-}
-
 /*
  * Increase the eb_refs of current subpage.
  *
@@ -152,7 +147,7 @@ void btrfs_free_subpage(struct btrfs_subpage *subpage)
  */
 void btrfs_folio_inc_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	if (!btrfs_meta_is_subpage(fs_info))
 		return;
@@ -160,13 +155,13 @@ void btrfs_folio_inc_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *
 	ASSERT(folio_test_private(folio) && folio->mapping);
 	lockdep_assert_held(&folio->mapping->i_private_lock);
 
-	subpage = folio_get_private(folio);
-	atomic_inc(&subpage->eb_refs);
+	bfs = folio_get_private(folio);
+	atomic_inc(&bfs->eb_refs);
 }
 
 void btrfs_folio_dec_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 
 	if (!btrfs_meta_is_subpage(fs_info))
 		return;
@@ -174,9 +169,9 @@ void btrfs_folio_dec_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *
 	ASSERT(folio_test_private(folio) && folio->mapping);
 	lockdep_assert_held(&folio->mapping->i_private_lock);
 
-	subpage = folio_get_private(folio);
-	ASSERT(atomic_read(&subpage->eb_refs));
-	atomic_dec(&subpage->eb_refs);
+	bfs = folio_get_private(folio);
+	ASSERT(atomic_read(&bfs->eb_refs));
+	atomic_dec(&bfs->eb_refs);
 }
 
 static void btrfs_subpage_assert(const struct btrfs_fs_info *fs_info,
@@ -228,7 +223,7 @@ static void btrfs_subpage_clamp_range(struct folio *folio, u64 *start, u32 *len)
 static bool btrfs_subpage_end_and_test_lock(const struct btrfs_fs_info *fs_info,
 					    struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
 	const int nbits = (len >> fs_info->sectorsize_bits);
 	unsigned long flags;
@@ -238,7 +233,7 @@ static bool btrfs_subpage_end_and_test_lock(const struct btrfs_fs_info *fs_info,
 
 	btrfs_subpage_assert(fs_info, folio, start, len);
 
-	spin_lock_irqsave(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
 	/*
 	 * We have call sites passing @lock_page into
 	 * extent_clear_unlock_delalloc() for compression path.
@@ -246,18 +241,18 @@ static bool btrfs_subpage_end_and_test_lock(const struct btrfs_fs_info *fs_info,
 	 * This @locked_page is locked by plain lock_page(), thus its
 	 * subpage::locked is 0.  Handle them in a special way.
 	 */
-	if (atomic_read(&subpage->nr_locked) == 0) {
-		spin_unlock_irqrestore(&subpage->lock, flags);
+	if (atomic_read(&bfs->nr_locked) == 0) {
+		spin_unlock_irqrestore(&bfs->lock, flags);
 		return true;
 	}
 
-	for_each_set_bit_from(bit, subpage->bitmaps, start_bit + nbits) {
-		clear_bit(bit, subpage->bitmaps);
+	for_each_set_bit_from(bit, bfs->bitmaps, start_bit + nbits) {
+		clear_bit(bit, bfs->bitmaps);
 		cleared++;
 	}
-	ASSERT(atomic_read(&subpage->nr_locked) >= cleared);
-	last = atomic_sub_and_test(cleared, &subpage->nr_locked);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	ASSERT(atomic_read(&bfs->nr_locked) >= cleared);
+	last = atomic_sub_and_test(cleared, &bfs->nr_locked);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 	return last;
 }
 
@@ -280,7 +275,7 @@ static bool btrfs_subpage_end_and_test_lock(const struct btrfs_fs_info *fs_info,
 void btrfs_folio_end_lock(const struct btrfs_fs_info *fs_info,
 			  struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 
 	ASSERT(folio_test_locked(folio));
 
@@ -296,7 +291,7 @@ void btrfs_folio_end_lock(const struct btrfs_fs_info *fs_info,
 	 * Since we own the page lock, no one else could touch subpage::locked
 	 * and we are safe to do several atomic operations without spinlock.
 	 */
-	if (atomic_read(&subpage->nr_locked) == 0) {
+	if (atomic_read(&bfs->nr_locked) == 0) {
 		/* No subpage lock, locked by plain lock_page(). */
 		folio_unlock(folio);
 		return;
@@ -310,7 +305,7 @@ void btrfs_folio_end_lock(const struct btrfs_fs_info *fs_info,
 void btrfs_folio_end_lock_bitmap(const struct btrfs_fs_info *fs_info,
 				 struct folio *folio, unsigned long bitmap)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	const unsigned int blocks_per_folio = btrfs_blocks_per_folio(fs_info, folio);
 	const int start_bit = blocks_per_folio * btrfs_bitmap_nr_locked;
 	unsigned long flags;
@@ -323,42 +318,42 @@ void btrfs_folio_end_lock_bitmap(const struct btrfs_fs_info *fs_info,
 		return;
 	}
 
-	if (atomic_read(&subpage->nr_locked) == 0) {
+	if (atomic_read(&bfs->nr_locked) == 0) {
 		/* No subpage lock, locked by plain lock_page(). */
 		folio_unlock(folio);
 		return;
 	}
 
-	spin_lock_irqsave(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
 	for_each_set_bit(bit, &bitmap, blocks_per_folio) {
-		if (test_and_clear_bit(bit + start_bit, subpage->bitmaps))
+		if (test_and_clear_bit(bit + start_bit, bfs->bitmaps))
 			cleared++;
 	}
-	ASSERT(atomic_read(&subpage->nr_locked) >= cleared);
-	last = atomic_sub_and_test(cleared, &subpage->nr_locked);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	ASSERT(atomic_read(&bfs->nr_locked) >= cleared);
+	last = atomic_sub_and_test(cleared, &bfs->nr_locked);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 	if (last)
 		folio_unlock(folio);
 }
 
 #define subpage_test_bitmap_all_set(fs_info, folio, name)		\
 ({									\
-	struct btrfs_subpage *subpage = folio_get_private(folio);	\
+	struct btrfs_folio_state *bfs = folio_get_private(folio);	\
 	const unsigned int blocks_per_folio =				\
 				btrfs_blocks_per_folio(fs_info, folio); \
 									\
-	bitmap_test_range_all_set(subpage->bitmaps,			\
+	bitmap_test_range_all_set(bfs->bitmaps,				\
 			blocks_per_folio * btrfs_bitmap_nr_##name,	\
 			blocks_per_folio);				\
 })
 
 #define subpage_test_bitmap_all_zero(fs_info, folio, name)		\
 ({									\
-	struct btrfs_subpage *subpage = folio_get_private(folio);	\
+	struct btrfs_folio_state *bfs = folio_get_private(folio);	\
 	const unsigned int blocks_per_folio =				\
 				btrfs_blocks_per_folio(fs_info, folio); \
 									\
-	bitmap_test_range_all_zero(subpage->bitmaps,			\
+	bitmap_test_range_all_zero(bfs->bitmaps,			\
 			blocks_per_folio * btrfs_bitmap_nr_##name,	\
 			blocks_per_folio);				\
 })
@@ -366,43 +361,43 @@ void btrfs_folio_end_lock_bitmap(const struct btrfs_fs_info *fs_info,
 void btrfs_subpage_set_uptodate(const struct btrfs_fs_info *fs_info,
 				struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							uptodate, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_set(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (subpage_test_bitmap_all_set(fs_info, folio, uptodate))
 		folio_mark_uptodate(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_clear_uptodate(const struct btrfs_fs_info *fs_info,
 				  struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							uptodate, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_clear(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_clear(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	folio_clear_uptodate(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_set_dirty(const struct btrfs_fs_info *fs_info,
 			     struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							dirty, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_set(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 	folio_mark_dirty(folio);
 }
 
@@ -419,17 +414,17 @@ void btrfs_subpage_set_dirty(const struct btrfs_fs_info *fs_info,
 bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info,
 					struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							dirty, start, len);
 	unsigned long flags;
 	bool last = false;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_clear(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_clear(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (subpage_test_bitmap_all_zero(fs_info, folio, dirty))
 		last = true;
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 	return last;
 }
 
@@ -446,91 +441,91 @@ void btrfs_subpage_clear_dirty(const struct btrfs_fs_info *fs_info,
 void btrfs_subpage_set_writeback(const struct btrfs_fs_info *fs_info,
 				 struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							writeback, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_set(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (!folio_test_writeback(folio))
 		folio_start_writeback(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_clear_writeback(const struct btrfs_fs_info *fs_info,
 				   struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							writeback, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_clear(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_clear(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (subpage_test_bitmap_all_zero(fs_info, folio, writeback)) {
 		ASSERT(folio_test_writeback(folio));
 		folio_end_writeback(folio);
 	}
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_set_ordered(const struct btrfs_fs_info *fs_info,
 			       struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							ordered, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_set(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	folio_set_ordered(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_clear_ordered(const struct btrfs_fs_info *fs_info,
 				 struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							ordered, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_clear(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_clear(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (subpage_test_bitmap_all_zero(fs_info, folio, ordered))
 		folio_clear_ordered(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_set_checked(const struct btrfs_fs_info *fs_info,
 			       struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							checked, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_set(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_set(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	if (subpage_test_bitmap_all_set(fs_info, folio, checked))
 		folio_set_checked(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 void btrfs_subpage_clear_checked(const struct btrfs_fs_info *fs_info,
 				 struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage = folio_get_private(folio);
+	struct btrfs_folio_state *bfs = folio_get_private(folio);
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,
 							checked, start, len);
 	unsigned long flags;
 
-	spin_lock_irqsave(&subpage->lock, flags);
-	bitmap_clear(subpage->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
+	spin_lock_irqsave(&bfs->lock, flags);
+	bitmap_clear(bfs->bitmaps, start_bit, len >> fs_info->sectorsize_bits);
 	folio_clear_checked(folio);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 /*
@@ -541,16 +536,16 @@ void btrfs_subpage_clear_checked(const struct btrfs_fs_info *fs_info,
 bool btrfs_subpage_test_##name(const struct btrfs_fs_info *fs_info,	\
 			       struct folio *folio, u64 start, u32 len)	\
 {									\
-	struct btrfs_subpage *subpage = folio_get_private(folio);	\
+	struct btrfs_folio_state *bfs = folio_get_private(folio);	\
 	unsigned int start_bit = subpage_calc_start_bit(fs_info, folio,	\
 						name, start, len);	\
 	unsigned long flags;						\
 	bool ret;							\
 									\
-	spin_lock_irqsave(&subpage->lock, flags);			\
-	ret = bitmap_test_range_all_set(subpage->bitmaps, start_bit,	\
+	spin_lock_irqsave(&bfs->lock, flags);			\
+	ret = bitmap_test_range_all_set(bfs->bitmaps, start_bit,	\
 				len >> fs_info->sectorsize_bits);	\
-	spin_unlock_irqrestore(&subpage->lock, flags);			\
+	spin_unlock_irqrestore(&bfs->lock, flags);			\
 	return ret;							\
 }
 IMPLEMENT_BTRFS_SUBPAGE_TEST_OP(uptodate);
@@ -662,10 +657,10 @@ IMPLEMENT_BTRFS_PAGE_OPS(checked, folio_set_checked, folio_clear_checked,
 {									\
 	const unsigned int blocks_per_folio =				\
 				btrfs_blocks_per_folio(fs_info, folio);	\
-	const struct btrfs_subpage *subpage = folio_get_private(folio);	\
+	const struct btrfs_folio_state *bfs = folio_get_private(folio);	\
 									\
 	ASSERT(blocks_per_folio <= BITS_PER_LONG);			\
-	*dst = bitmap_read(subpage->bitmaps,				\
+	*dst = bitmap_read(bfs->bitmaps,				\
 			   blocks_per_folio * btrfs_bitmap_nr_##name,	\
 			   blocks_per_folio);				\
 }
@@ -690,7 +685,7 @@ IMPLEMENT_BTRFS_PAGE_OPS(checked, folio_set_checked, folio_clear_checked,
 void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
 				  struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 	unsigned int start_bit;
 	unsigned int nbits;
 	unsigned long flags;
@@ -705,15 +700,15 @@ void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
 
 	start_bit = subpage_calc_start_bit(fs_info, folio, dirty, start, len);
 	nbits = len >> fs_info->sectorsize_bits;
-	subpage = folio_get_private(folio);
-	ASSERT(subpage);
-	spin_lock_irqsave(&subpage->lock, flags);
-	if (unlikely(!bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits))) {
+	bfs = folio_get_private(folio);
+	ASSERT(bfs);
+	spin_lock_irqsave(&bfs->lock, flags);
+	if (unlikely(!bitmap_test_range_all_zero(bfs->bitmaps, start_bit, nbits))) {
 		SUBPAGE_DUMP_BITMAP(fs_info, folio, dirty, start, len);
-		ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+		ASSERT(bitmap_test_range_all_zero(bfs->bitmaps, start_bit, nbits));
 	}
-	ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	ASSERT(bitmap_test_range_all_zero(bfs->bitmaps, start_bit, nbits));
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 /*
@@ -726,7 +721,7 @@ void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
 void btrfs_folio_set_lock(const struct btrfs_fs_info *fs_info,
 			  struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 	unsigned long flags;
 	unsigned int start_bit;
 	unsigned int nbits;
@@ -736,19 +731,19 @@ void btrfs_folio_set_lock(const struct btrfs_fs_info *fs_info,
 	if (unlikely(!fs_info) || !btrfs_is_subpage(fs_info, folio))
 		return;
 
-	subpage = folio_get_private(folio);
+	bfs = folio_get_private(folio);
 	start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
 	nbits = len >> fs_info->sectorsize_bits;
-	spin_lock_irqsave(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
 	/* Target range should not yet be locked. */
-	if (unlikely(!bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits))) {
+	if (unlikely(!bitmap_test_range_all_zero(bfs->bitmaps, start_bit, nbits))) {
 		SUBPAGE_DUMP_BITMAP(fs_info, folio, locked, start, len);
-		ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+		ASSERT(bitmap_test_range_all_zero(bfs->bitmaps, start_bit, nbits));
 	}
-	bitmap_set(subpage->bitmaps, start_bit, nbits);
-	ret = atomic_add_return(nbits, &subpage->nr_locked);
+	bitmap_set(bfs->bitmaps, start_bit, nbits);
+	ret = atomic_add_return(nbits, &bfs->nr_locked);
 	ASSERT(ret <= btrfs_blocks_per_folio(fs_info, folio));
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
 
 /*
@@ -776,7 +771,7 @@ bool btrfs_meta_folio_clear_and_test_dirty(struct folio *folio, const struct ext
 void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
 				      struct folio *folio, u64 start, u32 len)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 	const unsigned int blocks_per_folio = btrfs_blocks_per_folio(fs_info, folio);
 	unsigned long uptodate_bitmap;
 	unsigned long dirty_bitmap;
@@ -788,18 +783,18 @@ void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
 
 	ASSERT(folio_test_private(folio) && folio_get_private(folio));
 	ASSERT(blocks_per_folio > 1);
-	subpage = folio_get_private(folio);
+	bfs = folio_get_private(folio);
 
-	spin_lock_irqsave(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
 	GET_SUBPAGE_BITMAP(fs_info, folio, uptodate, &uptodate_bitmap);
 	GET_SUBPAGE_BITMAP(fs_info, folio, dirty, &dirty_bitmap);
 	GET_SUBPAGE_BITMAP(fs_info, folio, writeback, &writeback_bitmap);
 	GET_SUBPAGE_BITMAP(fs_info, folio, ordered, &ordered_bitmap);
 	GET_SUBPAGE_BITMAP(fs_info, folio, checked, &checked_bitmap);
 	GET_SUBPAGE_BITMAP(fs_info, folio, locked, &locked_bitmap);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 
-	dump_page(folio_page(folio, 0), "btrfs subpage dump");
+	dump_page(folio_page(folio, 0), "btrfs folio state dump");
 	btrfs_warn(fs_info,
 "start=%llu len=%u page=%llu, bitmaps uptodate=%*pbl dirty=%*pbl locked=%*pbl writeback=%*pbl ordered=%*pbl checked=%*pbl",
 		    start, len, folio_pos(folio),
@@ -815,14 +810,14 @@ void btrfs_get_subpage_dirty_bitmap(struct btrfs_fs_info *fs_info,
 				    struct folio *folio,
 				    unsigned long *ret_bitmap)
 {
-	struct btrfs_subpage *subpage;
+	struct btrfs_folio_state *bfs;
 	unsigned long flags;
 
 	ASSERT(folio_test_private(folio) && folio_get_private(folio));
 	ASSERT(btrfs_blocks_per_folio(fs_info, folio) > 1);
-	subpage = folio_get_private(folio);
+	bfs = folio_get_private(folio);
 
-	spin_lock_irqsave(&subpage->lock, flags);
+	spin_lock_irqsave(&bfs->lock, flags);
 	GET_SUBPAGE_BITMAP(fs_info, folio, dirty, ret_bitmap);
-	spin_unlock_irqrestore(&subpage->lock, flags);
+	spin_unlock_irqrestore(&bfs->lock, flags);
 }
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 52546e0e97ce..7889a97365f0 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -32,7 +32,16 @@ struct folio;
 enum {
 	btrfs_bitmap_nr_uptodate = 0,
 	btrfs_bitmap_nr_dirty,
+
+	/*
+	 * This can be changed to atomic eventually.
+	 * But this change will rely on the async delalloc range rework for
+	 * locked bitmap.
+	 * As async delalloc can unlock its range and mark blocks writeback
+	 * at random timing.
+	 */
 	btrfs_bitmap_nr_writeback,
+
 	/*
 	 * The ordered and checked flags are for COW fixup, already marked
 	 * deprecated, and will be removed eventually.
@@ -57,7 +66,7 @@ enum {
  * Structure to trace status of each sector inside a page, attached to
  * page::private for both data and metadata inodes.
  */
-struct btrfs_subpage {
+struct btrfs_folio_state {
 	/* Common members for both data and metadata pages */
 	spinlock_t lock;
 	union {
@@ -65,7 +74,7 @@ struct btrfs_subpage {
 		 * Structures only used by metadata
 		 *
 		 * @eb_refs should only be operated under private_lock, as it
-		 * manages whether the subpage can be detached.
+		 * manages whether the btrfs_folio_state can be detached.
 		 */
 		atomic_t eb_refs;
 
@@ -79,7 +88,7 @@ struct btrfs_subpage {
 	unsigned long bitmaps[];
 };
 
-enum btrfs_subpage_type {
+enum btrfs_folio_type {
 	BTRFS_SUBPAGE_METADATA,
 	BTRFS_SUBPAGE_DATA,
 };
@@ -119,15 +128,18 @@ static inline bool btrfs_is_subpage(const struct btrfs_fs_info *fs_info,
 }
 #endif
 
-int btrfs_attach_subpage(const struct btrfs_fs_info *fs_info,
-			 struct folio *folio, enum btrfs_subpage_type type);
-void btrfs_detach_subpage(const struct btrfs_fs_info *fs_info, struct folio *folio,
-			  enum btrfs_subpage_type type);
+int btrfs_attach_folio_state(const struct btrfs_fs_info *fs_info,
+			     struct folio *folio, enum btrfs_folio_type type);
+void btrfs_detach_folio_state(const struct btrfs_fs_info *fs_info, struct folio *folio,
+			      enum btrfs_folio_type type);
 
 /* Allocate additional data where page represents more than one sector */
-struct btrfs_subpage *btrfs_alloc_subpage(const struct btrfs_fs_info *fs_info,
-				size_t fsize, enum btrfs_subpage_type type);
-void btrfs_free_subpage(struct btrfs_subpage *subpage);
+struct btrfs_folio_state *btrfs_alloc_folio_state(const struct btrfs_fs_info *fs_info,
+						  size_t fsize, enum btrfs_folio_type type);
+static inline void btrfs_free_folio_state(struct btrfs_folio_state *bfs)
+{
+	kfree(bfs);
+}
 
 void btrfs_folio_inc_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio);
 void btrfs_folio_dec_eb_refs(const struct btrfs_fs_info *fs_info, struct folio *folio);
-- 
2.49.0

Re: [PATCH 2/2] btrfs: rename btrfs_subpage structure

[David Sterba]

On Mon, Jun 02, 2025 at 10:08:53AM +0930, Qu Wenruo wrote:
> With the incoming large data folios support, the structure name
> btrfs_subpage is no longer correct, as for we can have multiple blocks
> inside a large folio, and the block size is still page size.
> 
> So to follow the schema of iomap, rename btrfs_subpage to
> btrfs_folio_state, along with involved enums.
> 
> There are still exported functions with "btrfs_subpage_" prefix, and I
> believe for metadata the name "subpage" will stay forever as we will
> never allocate a folio larger than nodesize anyway.
> 
> The full cleanup of the word "subpage" will happen in much smaller steps
> in the future.

That's a good plan. We still have some mentions of 'page' in the context
of folios too, so we'll be clening that up for some time.

Re: [PATCH 0/2] btrfs: rename btrfs_subpage to btrfs_folio_state

[David Sterba]

On Mon, Jun 02, 2025 at 10:08:51AM +0930, Qu Wenruo wrote:
> This migration is mostly to align the naming to iomap, so btrfs_subpage
> is renamed to btrfs_folio_state.
> 
> But before the rename, explain why btrfs needs the following extra
> sub-bitmaps in the first patch.
> 
> Qu Wenruo (2):
>   btrfs: add comments on the extra btrfs specific subpage bitmaps
>   btrfs: rename btrfs_subpage structure

Reviewed-by: David Sterba <dsterba@suse.com>