[PATCH v4 04/20] jbd2: add fast commit block tracker variables

[Harshad Shirwadkar <harshadshirwadkar@gmail.com>]

Add j_first_fc, j_last_fc and j_fc_offset variables to track fast commit
area. j_first_fc and j_last_fc mark the start and the end of the area,
while j_fc_offset points to the last used block in the region.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
---
 fs/jbd2/journal.c    | 33 ++++++++++++++++++++++++++++-----
 include/linux/jbd2.h | 24 ++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index fa22bdb7d952..32f14be5065a 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1163,6 +1163,11 @@ static journal_t *journal_init_common(struct block_device *bdev,
 	if (!journal->j_wbuf)
 		goto err_cleanup;
 
+	if (journal->j_fc_wbufsize > 0) {
+		journal->j_wbufsize = n - journal->j_fc_wbufsize;
+		journal->j_fc_wbuf = &journal->j_wbuf[journal->j_wbufsize];
+	}
+
 	bh = getblk_unmovable(journal->j_dev, start, journal->j_blocksize);
 	if (!bh) {
 		pr_err("%s: Cannot get buffer for journal superblock\n",
@@ -1303,11 +1308,20 @@ static int journal_reset(journal_t *journal)
 	}
 
 	journal->j_first = first;
-	journal->j_last = last;
 
-	journal->j_head = first;
-	journal->j_tail = first;
-	journal->j_free = last - first;
+	if (jbd2_has_feature_fast_commit(journal) &&
+	    journal->j_fc_wbufsize > 0) {
+		journal->j_last_fc = last;
+		journal->j_last = last - journal->j_fc_wbufsize;
+		journal->j_first_fc = journal->j_last + 1;
+		journal->j_fc_off = 0;
+	} else {
+		journal->j_last = last;
+	}
+
+	journal->j_head = journal->j_first;
+	journal->j_tail = journal->j_first;
+	journal->j_free = journal->j_last - journal->j_first;
 
 	journal->j_tail_sequence = journal->j_transaction_sequence;
 	journal->j_commit_sequence = journal->j_transaction_sequence - 1;
@@ -1632,9 +1646,18 @@ static int load_superblock(journal_t *journal)
 	journal->j_tail_sequence = be32_to_cpu(sb->s_sequence);
 	journal->j_tail = be32_to_cpu(sb->s_start);
 	journal->j_first = be32_to_cpu(sb->s_first);
-	journal->j_last = be32_to_cpu(sb->s_maxlen);
 	journal->j_errno = be32_to_cpu(sb->s_errno);
 
+	if (jbd2_has_feature_fast_commit(journal) &&
+	    journal->j_fc_wbufsize > 0) {
+		journal->j_last_fc = be32_to_cpu(sb->s_maxlen);
+		journal->j_last = journal->j_last_fc - journal->j_fc_wbufsize;
+		journal->j_first_fc = journal->j_last + 1;
+		journal->j_fc_off = 0;
+	} else {
+		journal->j_last = be32_to_cpu(sb->s_maxlen);
+	}
+
 	return 0;
 }
 
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 3495fe1e2c36..7139626992f3 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -918,6 +918,30 @@ struct journal_s
 	 */
 	unsigned long		j_last;
 
+	/**
+	 * @j_first_fc:
+	 *
+	 * The block number of the first fast commit block in the journal
+	 * [j_state_lock].
+	 */
+	unsigned long		j_first_fc;
+
+	/**
+	 * @j_fc_off:
+	 *
+	 * Number of fast commit blocks currently allocated.
+	 * [j_state_lock].
+	 */
+	unsigned long		j_fc_off;
+
+	/**
+	 * @j_last_fc:
+	 *
+	 * The block number one beyond the last fast commit block in the journal
+	 * [j_state_lock].
+	 */
+	unsigned long		j_last_fc;
+
 	/**
 	 * @j_dev: Device where we store the journal.
 	 */
-- 
2.24.1.735.g03f4e72817-goog