ext4: add proc files to monitor new structures

This patch adds a new file "mb_structs_summary" which allows us to see
the summary of the new allocator structures added in this
series. Here's the sample output of file:

optimize_scan: 1
max_free_order_lists:
        list_order_0_groups: 0
        list_order_1_groups: 0
        list_order_2_groups: 0
        list_order_3_groups: 0
        list_order_4_groups: 0
        list_order_5_groups: 0
        list_order_6_groups: 0
        list_order_7_groups: 0
        list_order_8_groups: 0
        list_order_9_groups: 0
        list_order_10_groups: 0
        list_order_11_groups: 0
        list_order_12_groups: 0
        list_order_13_groups: 40
fragment_size_tree:
        tree_min: 16384
        tree_max: 32768
        tree_nodes: 40

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20210401172129.189766-7-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2872,6 +2872,7 @@ int __init ext4_fc_init_dentry_cache(void);
 
 /* mballoc.c */
 extern const struct seq_operations ext4_mb_seq_groups_ops;
+extern const struct seq_operations ext4_mb_seq_structs_summary_ops;
 extern long ext4_mb_stats;
 extern long ext4_mb_max_to_scan;
 extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);

fs/ext4/mballoc.c

@@ -2963,6 +2963,92 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 	return 0;
 }
 
+static void *ext4_mb_seq_structs_summary_start(struct seq_file *seq, loff_t *pos)
+{
+	struct super_block *sb = PDE_DATA(file_inode(seq->file));
+	unsigned long position;
+
+	read_lock(&EXT4_SB(sb)->s_mb_rb_lock);
+
+	if (*pos < 0 || *pos >= MB_NUM_ORDERS(sb) + 1)
+		return NULL;
+	position = *pos + 1;
+	return (void *) ((unsigned long) position);
+}
+
+static void *ext4_mb_seq_structs_summary_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct super_block *sb = PDE_DATA(file_inode(seq->file));
+	unsigned long position;
+
+	++*pos;
+	if (*pos < 0 || *pos >= MB_NUM_ORDERS(sb) + 1)
+		return NULL;
+	position = *pos + 1;
+	return (void *) ((unsigned long) position);
+}
+
+static int ext4_mb_seq_structs_summary_show(struct seq_file *seq, void *v)
+{
+	struct super_block *sb = PDE_DATA(file_inode(seq->file));
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	unsigned long position = ((unsigned long) v);
+	struct ext4_group_info *grp;
+	struct rb_node *n;
+	unsigned int count, min, max;
+
+	position--;
+	if (position >= MB_NUM_ORDERS(sb)) {
+		seq_puts(seq, "fragment_size_tree:\n");
+		n = rb_first(&sbi->s_mb_avg_fragment_size_root);
+		if (!n) {
+			seq_puts(seq, "\ttree_min: 0\n\ttree_max: 0\n\ttree_nodes: 0\n");
+			return 0;
+		}
+		grp = rb_entry(n, struct ext4_group_info, bb_avg_fragment_size_rb);
+		min = grp->bb_fragments ? grp->bb_free / grp->bb_fragments : 0;
+		count = 1;
+		while (rb_next(n)) {
+			count++;
+			n = rb_next(n);
+		}
+		grp = rb_entry(n, struct ext4_group_info, bb_avg_fragment_size_rb);
+		max = grp->bb_fragments ? grp->bb_free / grp->bb_fragments : 0;
+
+		seq_printf(seq, "\ttree_min: %u\n\ttree_max: %u\n\ttree_nodes: %u\n",
+			   min, max, count);
+		return 0;
+	}
+
+	if (position == 0) {
+		seq_printf(seq, "optimize_scan: %d\n",
+			   test_opt2(sb, MB_OPTIMIZE_SCAN) ? 1 : 0);
+		seq_puts(seq, "max_free_order_lists:\n");
+	}
+	count = 0;
+	list_for_each_entry(grp, &sbi->s_mb_largest_free_orders[position],
+			    bb_largest_free_order_node)
+		count++;
+	seq_printf(seq, "\tlist_order_%u_groups: %u\n",
+		   (unsigned int)position, count);
+
+	return 0;
+}
+
+static void ext4_mb_seq_structs_summary_stop(struct seq_file *seq, void *v)
+{
+	struct super_block *sb = PDE_DATA(file_inode(seq->file));
+
+	read_unlock(&EXT4_SB(sb)->s_mb_rb_lock);
+}
+
+const struct seq_operations ext4_mb_seq_structs_summary_ops = {
+	.start  = ext4_mb_seq_structs_summary_start,
+	.next   = ext4_mb_seq_structs_summary_next,
+	.stop   = ext4_mb_seq_structs_summary_stop,
+	.show   = ext4_mb_seq_structs_summary_show,
+};
+
 static struct kmem_cache *get_groupinfo_cache(int blocksize_bits)
 {
 	int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;

fs/ext4/sysfs.c

@@ -534,6 +534,8 @@ int ext4_register_sysfs(struct super_block *sb)
 				&ext4_mb_seq_groups_ops, sb);
 		proc_create_single_data("mb_stats", 0444, sbi->s_proc,
 				ext4_seq_mb_stats_show, sb);
+		proc_create_seq_data("mb_structs_summary", 0444, sbi->s_proc,
+				&ext4_mb_seq_structs_summary_ops, sb);
 	}
 	return 0;
 }