Merge patch series "Remove b_end_io from struct buffer_head"

Matthew Wilcox (Oracle) <willy@infradead.org> says:

There are four benefits to this patchset.  First, it removes an
indirect function call from the completion path.  Instead of setting
bio->bi_end_io to end_bio_bh_io_sync() which then calls bh->b_end_io(),
we set bio->bi_end_io to the appropriate completion handler, replacing
two indirect function calls with one.

Second, there is a slight security advantage to this.  It is one fewer
function pointer in the middle of a writable data structure that can
be corrupted.  Third, it shrinks struct buffer_head from 104 bytes to 96
bytes, allowing for appropriximately 7% reduction in the amount of memory
used by buffer_heads (or, alternatively, allows 7% more buffer_heads to
be cached in the same amount of memory).  Fourth, it removes some
atomic operations as the buffer refcount is no longer incremented before
calling the end_io handler.

I've run ext4 through its paces, and everything seems OK.  I've only
compiled ocfs2/gfs2/nilfs/md-bitmap.  Hopefully the maintainers can give
this series a try.  I'm sending the entire series to linux-fsdevel
and cc'ing the fs-specific mailing lists for the fs-specific patches.

* patches from https://patch.msgid.link/20260528173150.1093780-1-willy@infradead.org: (34 commits)
  buffer: Remove end_buffer_write_sync()
  buffer: Change calling convention for end_buffer_read_sync()
  buffer: Remove b_end_io
  buffer: Remove submit_bh()
  md-bitmap: Convert read_file_page and write_file_page to bh_submit()
  nilfs2: Convert nilfs_mdt_submit_block to bh_submit()
  nilfs2: Convert nilfs_gccache_submit_read_data to bh_submit()
  nilfs2: Convert nilfs_btnode_submit_block to bh_submit()
  buffer: Remove mark_buffer_async_write()
  gfs2: Convert gfs2_aspace_write_folio to bh_submit()
  gfs2: Remove use of b_end_io in gfs2_meta_read_endio()
  gfs2: Convert gfs2_dir_readahead to bh_submit()
  gfs2: Convert gfs2_metapath_ra to bh_submit()
  ocfs2: Convert ocfs2_write_super_or_backup to bh_submit()
  ocfs2: Convert ocfs2_read_blocks to bh_submit()
  ocfs2: Convert ocfs2_read_block to bh_submit()
  ocfs2: Convert ocfs2_write_block to bh_submit()
  jbd2: Convert jbd2_write_superblock() to bh_submit()
  jbd2: Convert journal commit to bh_submit()
  ext4: Convert ext4_commit_super() to bh_submit()
  ...

Link: https://patch.msgid.link/20260528173150.1093780-1-willy@infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 9 insertions, 7 deletions

diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index e4939e33b4b5..8b23bc9a244c 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -46,7 +46,6 @@ enum bh_state_bits {
 struct page;
 struct buffer_head;
 struct address_space;
-typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);
 
 /*
  * Historically, a buffer_head was used to map a single block
@@ -55,7 +54,7 @@ typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);
  * is the bio, and buffer_heads are used for extracting block
  * mappings (via a get_block_t call), for tracking state within
  * a folio (via a folio_mapping) and for wrapping bio submission
- * for backward compatibility reasons (e.g. submit_bh).
+ * for backward compatibility reasons (e.g. bh_submit).
  */
 struct buffer_head {
 	unsigned long b_state;		/* buffer state bitmap (see above) */
@@ -70,8 +69,7 @@ struct buffer_head {
 	char *b_data;			/* pointer to data within the page */
 
 	struct block_device *b_bdev;
-	bh_end_io_t *b_end_io;		/* I/O completion */
- 	void *b_private;		/* reserved for b_end_io */
+	void *b_private;		/* reserved for bio_end_io */
 	struct list_head b_assoc_buffers; /* associated with another mapping */
 	struct mapping_metadata_bhs *b_mmb; /* head of the list of metadata bhs
 					     * this buffer is associated with */
@@ -203,7 +201,12 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size);
 struct buffer_head *create_empty_buffers(struct folio *folio,
 		unsigned long blocksize, unsigned long b_state);
 void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
-void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
+bool bio_endio_bh(struct bio *bio, struct buffer_head **bhp);
+
+/* Completion routines suitable for passing to bh_submit() */
+void bh_end_read(struct bio *bio);
+void bh_end_write(struct bio *bio);
+void bh_end_async_write(struct bio *bio);
 
 /* Things to do with metadata buffers list */
 void mmb_mark_buffer_dirty(struct buffer_head *bh, struct mapping_metadata_bhs *mmb);
@@ -218,7 +221,6 @@ static inline void clean_bdev_bh_alias(struct buffer_head *bh)
 	clean_bdev_aliases(bh->b_bdev, bh->b_blocknr, 1);
 }
 
-void mark_buffer_async_write(struct buffer_head *bh);
 void __wait_on_buffer(struct buffer_head *);
 wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
 struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
@@ -239,7 +241,7 @@ void __lock_buffer(struct buffer_head *bh);
 int sync_dirty_buffer(struct buffer_head *bh);
 int __sync_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
 void write_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
-void submit_bh(blk_opf_t, struct buffer_head *);
+void bh_submit(struct buffer_head *, blk_opf_t, bio_end_io_t);
 void write_boundary_block(struct block_device *bdev,
 			sector_t bblock, unsigned blocksize);
 int bh_uptodate_or_lock(struct buffer_head *bh);