bcachefs: Include average write size in sysfs journal_debug

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/journal.c

@@ -1262,6 +1262,7 @@ void __bch2_journal_debug_to_text(struct printbuf *out, struct journal *j)
 	union journal_res_state s;
 	struct bch_dev *ca;
 	unsigned long now = jiffies;
+	u64 nr_writes = j->nr_flush_writes + j->nr_noflush_writes;
 	u64 seq;
 	unsigned i;
 
@@ -1282,6 +1283,9 @@ void __bch2_journal_debug_to_text(struct printbuf *out, struct journal *j)
 	prt_printf(out, "each entry reserved:\t%u\n",		j->entry_u64s_reserved);
 	prt_printf(out, "nr flush writes:\t%llu\n",		j->nr_flush_writes);
 	prt_printf(out, "nr noflush writes:\t%llu\n",		j->nr_noflush_writes);
+	prt_printf(out, "average write size:\t");
+	prt_human_readable_u64(out, nr_writes ? div64_u64(j->entry_bytes_written, nr_writes) : 0);
+	prt_newline(out);
 	prt_printf(out, "nr direct reclaim:\t%llu\n",		j->nr_direct_reclaim);
 	prt_printf(out, "nr background reclaim:\t%llu\n",	j->nr_background_reclaim);
 	prt_printf(out, "reclaim kicked:\t\t%u\n",		j->reclaim_kicked);

fs/bcachefs/journal_io.c

@@ -1890,6 +1890,8 @@ CLOSURE_CALLBACK(bch2_journal_write)
 	if (ret)
 		goto err;
 
+	j->entry_bytes_written += vstruct_bytes(w->data);
+
 	while (1) {
 		spin_lock(&j->lock);
 		ret = journal_write_alloc(j, w);

fs/bcachefs/journal_types.h

@@ -267,6 +267,7 @@ struct journal {
 
 	u64			nr_flush_writes;
 	u64			nr_noflush_writes;
+	u64			entry_bytes_written;
 
 	struct bch2_time_stats	*flush_write_time;
 	struct bch2_time_stats	*noflush_write_time;