ext4: Add per CR extent scanned counter

This gives better visibility into the number of extents scanned in each
particular CR. For example, this information can be used to see how out
block group scanning logic is performing when the BG is fragmented.

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/55bb6d80f6e22ed2a5a830aa045572bdffc8b1b9.1685449706.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1555,6 +1555,7 @@ struct ext4_sb_info {
 	atomic_t s_bal_success;	/* we found long enough chunks */
 	atomic_t s_bal_allocated;	/* in blocks */
 	atomic_t s_bal_ex_scanned;	/* total extents scanned */
+	atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS];	/* total extents scanned */
 	atomic_t s_bal_groups_scanned;	/* number of groups scanned */
 	atomic_t s_bal_goals;	/* goal hits */
 	atomic_t s_bal_breaks;	/* too long searches */

fs/ext4/mballoc.c

@@ -2104,6 +2104,7 @@ static void ext4_mb_measure_extent(struct ext4_allocation_context *ac,
 	BUG_ON(ac->ac_status != AC_STATUS_CONTINUE);
 
 	ac->ac_found++;
+	ac->ac_cX_found[ac->ac_criteria]++;
 
 	/*
 	 * The special case - take what you catch first
@@ -2278,6 +2279,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
 			break;
 		}
 		ac->ac_found++;
+		ac->ac_cX_found[ac->ac_criteria]++;
 
 		ac->ac_b_ex.fe_len = 1 << i;
 		ac->ac_b_ex.fe_start = k << i;
@@ -2393,6 +2395,7 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
 			max = mb_find_extent(e4b, i, stripe, &ex);
 			if (max >= stripe) {
 				ac->ac_found++;
+				ac->ac_cX_found[ac->ac_criteria]++;
 				ex.fe_logical = 0xDEADF00D; /* debug value */
 				ac->ac_b_ex = ex;
 				ext4_mb_use_best_found(ac, e4b);
@@ -2930,6 +2933,7 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR0]));
 	seq_printf(seq, "\t\tgroups_considered: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[CR0]));
+	seq_printf(seq, "\t\textents_scanned: %u\n", atomic_read(&sbi->s_bal_cX_ex_scanned[CR0]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[CR0]));
 	seq_printf(seq, "\t\tbad_suggestions: %u\n",
@@ -2939,6 +2943,7 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR1]));
 	seq_printf(seq, "\t\tgroups_considered: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[CR1]));
+	seq_printf(seq, "\t\textents_scanned: %u\n", atomic_read(&sbi->s_bal_cX_ex_scanned[CR1]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[CR1]));
 	seq_printf(seq, "\t\tbad_suggestions: %u\n",
@@ -2948,13 +2953,15 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR2]));
 	seq_printf(seq, "\t\tgroups_considered: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[CR2]));
+	seq_printf(seq, "\t\textents_scanned: %u\n", atomic_read(&sbi->s_bal_cX_ex_scanned[CR2]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[CR2]));
 
 	seq_puts(seq, "\tcr3_stats:\n");
 	seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR3]));
 	seq_printf(seq, "\t\tgroups_considered: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_groups_considered[CR3]));
+	seq_printf(seq, "\t\textents_scanned: %u\n", atomic_read(&sbi->s_bal_cX_ex_scanned[CR3]));
 	seq_printf(seq, "\t\tuseless_loops: %llu\n",
 		   atomic64_read(&sbi->s_bal_cX_failed[CR3]));
 	seq_printf(seq, "\textents_scanned: %u\n", atomic_read(&sbi->s_bal_ex_scanned));
@@ -4403,7 +4410,12 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
 		atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
 		if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
 			atomic_inc(&sbi->s_bal_success);
+
 		atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
+		for (int i=0; i<EXT4_MB_NUM_CRS; i++) {
+			atomic_add(ac->ac_cX_found[i], &sbi->s_bal_cX_ex_scanned[i]);
+		}
+
 		atomic_add(ac->ac_groups_scanned, &sbi->s_bal_groups_scanned);
 		if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
 				ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)

fs/ext4/mballoc.h

@@ -184,6 +184,7 @@ struct ext4_allocation_context {
 	__u16 ac_groups_scanned;
 	__u16 ac_groups_linear_remaining;
 	__u16 ac_found;
+	__u16 ac_cX_found[EXT4_MB_NUM_CRS];
 	__u16 ac_tail;
 	__u16 ac_buddy;
 	__u8 ac_status;