jbd2: don't create journal_head for temporary journal buffers

When writing metadata to the journal, we create temporary buffer heads
for that task.  We also attach journal heads to these buffer heads but
the only purpose of the journal heads is to keep buffers linked in
transaction's BJ_IO list.  We remove the need for journal heads by
reusing buffer_head's b_assoc_buffers list for that purpose.  Also
since BJ_IO list is just a temporary list for transaction commit, we
use a private list in jbd2_journal_commit_transaction() for that thus
removing BJ_IO list from transaction completely.

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 14 insertions, 22 deletions

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 3cdd285df204f..45cdc080e4668 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -310,14 +310,12 @@ static void journal_kill_thread(journal_t *journal)
  *
  * If the source buffer has already been modified by a new transaction
  * since we took the last commit snapshot, we use the frozen copy of
- * that data for IO.  If we end up using the existing buffer_head's data
- * for the write, then we *have* to lock the buffer to prevent anyone
- * else from using and possibly modifying it while the IO is in
- * progress.
+ * that data for IO. If we end up using the existing buffer_head's data
+ * for the write, then we have to make sure nobody modifies it while the
+ * IO is in progress. do_get_write_access() handles this.
  *
- * The function returns a pointer to the buffer_heads to be used for IO.
- *
- * We assume that the journal has already been locked in this function.
+ * The function returns a pointer to the buffer_head to be used for IO.
+ * 
  *
  * Return value:
  *  <0: Error
@@ -330,15 +328,14 @@ static void journal_kill_thread(journal_t *journal)
 
 int jbd2_journal_write_metadata_buffer(transaction_t *transaction,
 				  struct journal_head  *jh_in,
-				  struct journal_head **jh_out,
-				  unsigned long long blocknr)
+				  struct buffer_head **bh_out,
+				  sector_t blocknr)
 {
 	int need_copy_out = 0;
 	int done_copy_out = 0;
 	int do_escape = 0;
 	char *mapped_data;
 	struct buffer_head *new_bh;
-	struct journal_head *new_jh;
 	struct page *new_page;
 	unsigned int new_offset;
 	struct buffer_head *bh_in = jh2bh(jh_in);
@@ -368,14 +365,13 @@ retry_alloc:
 
 	/* keep subsequent assertions sane */
 	atomic_set(&new_bh->b_count, 1);
-	new_jh = jbd2_journal_add_journal_head(new_bh);	/* This sleeps */
 
+	jbd_lock_bh_state(bh_in);
+repeat:
 	/*
 	 * If a new transaction has already done a buffer copy-out, then
 	 * we use that version of the data for the commit.
 	 */
-	jbd_lock_bh_state(bh_in);
-repeat:
 	if (jh_in->b_frozen_data) {
 		done_copy_out = 1;
 		new_page = virt_to_page(jh_in->b_frozen_data);
@@ -415,7 +411,7 @@ repeat:
 		jbd_unlock_bh_state(bh_in);
 		tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
 		if (!tmp) {
-			jbd2_journal_put_journal_head(new_jh);
+			brelse(new_bh);
 			return -ENOMEM;
 		}
 		jbd_lock_bh_state(bh_in);
@@ -426,7 +422,7 @@ repeat:
 
 		jh_in->b_frozen_data = tmp;
 		mapped_data = kmap_atomic(new_page);
-		memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
+		memcpy(tmp, mapped_data + new_offset, bh_in->b_size);
 		kunmap_atomic(mapped_data);
 
 		new_page = virt_to_page(tmp);
@@ -452,14 +448,13 @@ repeat:
 	}
 
 	set_bh_page(new_bh, new_page, new_offset);
-	new_jh->b_transaction = NULL;
-	new_bh->b_size = jh2bh(jh_in)->b_size;
-	new_bh->b_bdev = transaction->t_journal->j_dev;
+	new_bh->b_size = bh_in->b_size;
+	new_bh->b_bdev = journal->j_dev;
 	new_bh->b_blocknr = blocknr;
 	set_buffer_mapped(new_bh);
 	set_buffer_dirty(new_bh);
 
-	*jh_out = new_jh;
+	*bh_out = new_bh;
 
 	/*
 	 * The to-be-written buffer needs to get moved to the io queue,
@@ -472,9 +467,6 @@ repeat:
 	spin_unlock(&journal->j_list_lock);
 	jbd_unlock_bh_state(bh_in);
 
-	JBUFFER_TRACE(new_jh, "file as BJ_IO");
-	jbd2_journal_file_buffer(new_jh, transaction, BJ_IO);
-
 	return do_escape | (done_copy_out << 1);
 }