bcachefs: Add copygc wait to sysfs

Currently debugging an issue with copygc not running when it's supposed
to, and this is an obvious first step.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -773,6 +773,7 @@ mempool_t		bio_bounce_pages;
 	copygc_heap		copygc_heap;
 	struct bch_pd_controller copygc_pd;
 	struct write_point	copygc_write_point;
+	s64			copygc_wait;
 
 	/* STRIPES: */
 	GENRADIX(struct stripe) stripes[2];

fs/bcachefs/movinggc.c

@@ -311,11 +311,14 @@ static int bch2_copygc_thread(void *arg)
 		wait = bch2_copygc_wait_amount(c);
 
 		if (wait > clock->max_slop) {
+			c->copygc_wait = last + wait;
 			bch2_kthread_io_clock_wait(clock, last + wait,
 					MAX_SCHEDULE_TIMEOUT);
 			continue;
 		}
 
+		c->copygc_wait = 0;
+
 		if (bch2_copygc(c))
 			break;
 	}

fs/bcachefs/sysfs.c

@@ -188,6 +188,7 @@ rw_attribute(cache_replacement_policy);
 rw_attribute(label);
 
 rw_attribute(copy_gc_enabled);
+read_attribute(copy_gc_wait);
 sysfs_pd_controller_attribute(copy_gc);
 
 rw_attribute(rebalance_enabled);
@@ -336,6 +337,9 @@ SHOW(bch2_fs)
 	sysfs_printf(rebalance_enabled,		"%i", c->rebalance.enabled);
 	sysfs_pd_controller_show(rebalance,	&c->rebalance.pd); /* XXX */
 	sysfs_pd_controller_show(copy_gc,	&c->copygc_pd);
+	sysfs_hprint(copy_gc_wait,
+		     max(0LL, c->copygc_wait -
+			 atomic64_read(&c->io_clock[WRITE].now)) << 9);
 
 	if (attr == &sysfs_rebalance_work) {
 		bch2_rebalance_work_to_text(&out, c);
@@ -563,6 +567,7 @@ struct attribute *bch2_fs_internal_files[] = {
 	&sysfs_prune_cache,
 
 	&sysfs_copy_gc_enabled,
+	&sysfs_copy_gc_wait,
 
 	&sysfs_rebalance_enabled,
 	&sysfs_rebalance_work,