ext4: simplify updating of fast commit stats

Move fast commit stats updating logic to a separate function from
ext4_fc_commit(). This significantly improves readability of
ext4_fc_commit().

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223202140.2061101-4-harshads@google.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1747,7 +1747,6 @@ struct ext4_sb_info {
 	spinlock_t s_fc_lock;
 	struct buffer_head *s_fc_bh;
 	struct ext4_fc_stats s_fc_stats;
-	u64 s_fc_avg_commit_time;
 #ifdef CONFIG_EXT4_DEBUG
 	int s_fc_debug_max_replay;
 #endif

fs/ext4/fast_commit.c

@@ -1075,6 +1075,32 @@ static int ext4_fc_perform_commit(journal_t *journal)
 	return ret;
 }
 
+static void ext4_fc_update_stats(struct super_block *sb, int status,
+				 u64 commit_time, int nblks)
+{
+	struct ext4_fc_stats *stats = &EXT4_SB(sb)->s_fc_stats;
+
+	jbd_debug(1, "Fast commit ended with status = %d", status);
+	if (status == EXT4_FC_STATUS_OK) {
+		stats->fc_num_commits++;
+		stats->fc_numblks += nblks;
+		if (likely(stats->s_fc_avg_commit_time))
+			stats->s_fc_avg_commit_time =
+				(commit_time +
+				 stats->s_fc_avg_commit_time * 3) / 4;
+		else
+			stats->s_fc_avg_commit_time = commit_time;
+	} else if (status == EXT4_FC_STATUS_FAILED ||
+		   status == EXT4_FC_STATUS_INELIGIBLE) {
+		if (status == EXT4_FC_STATUS_FAILED)
+			stats->fc_failed_commits++;
+		stats->fc_ineligible_commits++;
+	} else {
+		stats->fc_skipped_commits++;
+	}
+	trace_ext4_fc_commit_stop(sb, nblks, status);
+}
+
 /*
  * The main commit entry point. Performs a fast commit for transaction
  * commit_tid if needed. If it's not possible to perform a fast commit
@@ -1087,7 +1113,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	int nblks = 0, ret, bsize = journal->j_blocksize;
 	int subtid = atomic_read(&sbi->s_fc_subtid);
-	int reason = EXT4_FC_REASON_OK, fc_bufs_before = 0;
+	int status = EXT4_FC_STATUS_OK, fc_bufs_before = 0;
 	ktime_t start_time, commit_time;
 
 	trace_ext4_fc_commit_start(sb);
@@ -1104,69 +1130,52 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
 		if (atomic_read(&sbi->s_fc_subtid) <= subtid &&
 			commit_tid > journal->j_commit_sequence)
 			goto restart_fc;
-		reason = EXT4_FC_REASON_ALREADY_COMMITTED;
-		goto out;
+		ext4_fc_update_stats(sb, EXT4_FC_STATUS_SKIPPED, 0, 0);
+		return 0;
 	} else if (ret) {
-		sbi->s_fc_stats.fc_ineligible_reason_count[EXT4_FC_COMMIT_FAILED]++;
-		reason = EXT4_FC_REASON_FC_START_FAILED;
-		goto out;
+		/*
+		 * Commit couldn't start. Just update stats and perform a
+		 * full commit.
+		 */
+		ext4_fc_update_stats(sb, EXT4_FC_STATUS_FAILED, 0, 0);
+		return jbd2_complete_transaction(journal, commit_tid);
 	}
+
 	/*
 	 * After establishing journal barrier via jbd2_fc_begin_commit(), check
 	 * if we are fast commit ineligible.
 	 */
 	if (ext4_test_mount_flag(sb, EXT4_MF_FC_INELIGIBLE)) {
-		reason = EXT4_FC_REASON_INELIGIBLE;
-		goto out;
+		status = EXT4_FC_STATUS_INELIGIBLE;
+		goto fallback;
 	}
 
 	fc_bufs_before = (sbi->s_fc_bytes + bsize - 1) / bsize;
 	ret = ext4_fc_perform_commit(journal);
 	if (ret < 0) {
-		sbi->s_fc_stats.fc_ineligible_reason_count[EXT4_FC_COMMIT_FAILED]++;
-		reason = EXT4_FC_REASON_FC_FAILED;
-		goto out;
+		status = EXT4_FC_STATUS_FAILED;
+		goto fallback;
 	}
 	nblks = (sbi->s_fc_bytes + bsize - 1) / bsize - fc_bufs_before;
 	ret = jbd2_fc_wait_bufs(journal, nblks);
 	if (ret < 0) {
-		sbi->s_fc_stats.fc_ineligible_reason_count[EXT4_FC_COMMIT_FAILED]++;
-		reason = EXT4_FC_REASON_FC_FAILED;
-		goto out;
+		status = EXT4_FC_STATUS_FAILED;
+		goto fallback;
 	}
 	atomic_inc(&sbi->s_fc_subtid);
-	jbd2_fc_end_commit(journal);
-out:
-	spin_lock(&sbi->s_fc_lock);
-	if (reason != EXT4_FC_REASON_OK &&
-		reason != EXT4_FC_REASON_ALREADY_COMMITTED) {
-		sbi->s_fc_stats.fc_ineligible_commits++;
-	} else {
-		sbi->s_fc_stats.fc_num_commits++;
-		sbi->s_fc_stats.fc_numblks += nblks;
-	}
-	spin_unlock(&sbi->s_fc_lock);
-	nblks = (reason == EXT4_FC_REASON_OK) ? nblks : 0;
-	trace_ext4_fc_commit_stop(sb, nblks, reason);
-	commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
+	ret = jbd2_fc_end_commit(journal);
 	/*
-	 * weight the commit time higher than the average time so we don't
-	 * react too strongly to vast changes in the commit time
+	 * weight the commit time higher than the average time so we
+	 * don't react too strongly to vast changes in the commit time
 	 */
-	if (likely(sbi->s_fc_avg_commit_time))
-		sbi->s_fc_avg_commit_time = (commit_time +
-				sbi->s_fc_avg_commit_time * 3) / 4;
-	else
-		sbi->s_fc_avg_commit_time = commit_time;
-	jbd_debug(1,
-		"Fast commit ended with blks = %d, reason = %d, subtid - %d",
-		nblks, reason, subtid);
-	if (reason == EXT4_FC_REASON_FC_FAILED)
-		return jbd2_fc_end_commit_fallback(journal);
-	if (reason == EXT4_FC_REASON_FC_START_FAILED ||
-		reason == EXT4_FC_REASON_INELIGIBLE)
-		return jbd2_complete_transaction(journal, commit_tid);
-	return 0;
+	commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
+	ext4_fc_update_stats(sb, status, commit_time, nblks);
+	return ret;
+
+fallback:
+	ret = jbd2_fc_end_commit_fallback(journal);
+	ext4_fc_update_stats(sb, status, 0, 0);
+	return ret;
 }
 
 /*
@@ -2124,7 +2133,7 @@ int ext4_fc_info_show(struct seq_file *seq, void *v)
 		"fc stats:\n%ld commits\n%ld ineligible\n%ld numblks\n%lluus avg_commit_time\n",
 		   stats->fc_num_commits, stats->fc_ineligible_commits,
 		   stats->fc_numblks,
-		   div_u64(sbi->s_fc_avg_commit_time, 1000));
+		   div_u64(stats->s_fc_avg_commit_time, 1000));
 	seq_puts(seq, "Ineligible reasons:\n");
 	for (i = 0; i < EXT4_FC_REASON_MAX; i++)
 		seq_printf(seq, "\"%s\":\t%d\n", fc_ineligible_reasons[i],

fs/ext4/fast_commit.h

@@ -71,21 +71,19 @@ struct ext4_fc_tail {
 };
 
 /*
- * Fast commit reason codes
+ * Fast commit status codes
+ */
+enum {
+	EXT4_FC_STATUS_OK = 0,
+	EXT4_FC_STATUS_INELIGIBLE,
+	EXT4_FC_STATUS_SKIPPED,
+	EXT4_FC_STATUS_FAILED,
+};
+
+/*
+ * Fast commit ineligiblity reasons:
  */
 enum {
-	/*
-	 * Commit status codes:
-	 */
-	EXT4_FC_REASON_OK = 0,
-	EXT4_FC_REASON_INELIGIBLE,
-	EXT4_FC_REASON_ALREADY_COMMITTED,
-	EXT4_FC_REASON_FC_START_FAILED,
-	EXT4_FC_REASON_FC_FAILED,
-
-	/*
-	 * Fast commit ineligiblity reasons:
-	 */
 	EXT4_FC_REASON_XATTR = 0,
 	EXT4_FC_REASON_CROSS_RENAME,
 	EXT4_FC_REASON_JOURNAL_FLAG_CHANGE,
@@ -117,7 +115,10 @@ struct ext4_fc_stats {
 	unsigned int fc_ineligible_reason_count[EXT4_FC_REASON_MAX];
 	unsigned long fc_num_commits;
 	unsigned long fc_ineligible_commits;
+	unsigned long fc_failed_commits;
+	unsigned long fc_skipped_commits;
 	unsigned long fc_numblks;
+	u64 s_fc_avg_commit_time;
 };
 
 #define EXT4_FC_REPLAY_REALLOC_INCREMENT	4