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>