ext4: add fast commit stats in procfs

This commit adds a file in procfs that tracks fast commit related
statistics.

root@kvm-xfstests:/mnt# cat /proc/fs/ext4/vdc/fc_info
fc stats:
7772 commits
15 ineligible
4083 numblks
2242us avg_commit_time
Ineligible reasons:
"Extended attributes changed":  0
"Cross rename": 0
"Journal flag changed": 0
"Insufficient memory":  0
"Swap boot":    0
"Resize":       0
"Dir renamed":  0
"Falloc range op":      0
"FC Commit Failed":     15
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201015203802.3597742-10-harshadshirwadkar@gmail.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2740,7 +2740,7 @@ extern int ext4_init_inode_table(struct super_block *sb,
 extern void ext4_end_bitmap_read(struct buffer_head *bh, int uptodate);
 
 /* fast_commit.c */
-
+int ext4_fc_info_show(struct seq_file *seq, void *v);
 void ext4_fc_init(struct super_block *sb, journal_t *journal);
 void ext4_fc_init_inode(struct inode *inode);
 void ext4_fc_track_range(struct inode *inode, ext4_lblk_t start,

fs/ext4/fast_commit.c

@@ -2093,6 +2093,40 @@ void ext4_fc_init(struct super_block *sb, journal_t *journal)
 	}
 }
 
+const char *fc_ineligible_reasons[] = {
+	"Extended attributes changed",
+	"Cross rename",
+	"Journal flag changed",
+	"Insufficient memory",
+	"Swap boot",
+	"Resize",
+	"Dir renamed",
+	"Falloc range op",
+	"FC Commit Failed"
+};
+
+int ext4_fc_info_show(struct seq_file *seq, void *v)
+{
+	struct ext4_sb_info *sbi = EXT4_SB((struct super_block *)seq->private);
+	struct ext4_fc_stats *stats = &sbi->s_fc_stats;
+	int i;
+
+	if (v != SEQ_START_TOKEN)
+		return 0;
+
+	seq_printf(seq,
+		"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));
+	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],
+			stats->fc_ineligible_reason_count[i]);
+
+	return 0;
+}
+
 int __init ext4_fc_init_dentry_cache(void)
 {
 	ext4_fc_dentry_cachep = KMEM_CACHE(ext4_fc_dentry_update,

fs/ext4/sysfs.c

@@ -521,6 +521,8 @@ int ext4_register_sysfs(struct super_block *sb)
 		proc_create_single_data("es_shrinker_info", S_IRUGO,
 				sbi->s_proc, ext4_seq_es_shrinker_info_show,
 				sb);
+		proc_create_single_data("fc_info", 0444, sbi->s_proc,
+					ext4_fc_info_show, sb);
 		proc_create_seq_data("mb_groups", S_IRUGO, sbi->s_proc,
 				&ext4_mb_seq_groups_ops, sb);
 	}