bcachefs: Ensure copygc does not spin

If copygc does no work - finds no fragmented buckets - wait for a bit of
IO to happen.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/alloc_background.c

@@ -2085,6 +2085,17 @@ void bch2_recalc_capacity(struct bch_fs *c)
 	closure_wake_up(&c->freelist_wait);
 }
 
+u64 bch2_min_rw_member_capacity(struct bch_fs *c)
+{
+	struct bch_dev *ca;
+	unsigned i;
+	u64 ret = U64_MAX;
+
+	for_each_rw_member(ca, c, i)
+		ret = min(ret, ca->mi.nbuckets * ca->mi.bucket_size);
+	return ret;
+}
+
 static bool bch2_dev_has_open_write_point(struct bch_fs *c, struct bch_dev *ca)
 {
 	struct open_bucket *ob;

fs/bcachefs/alloc_background.h

@@ -249,6 +249,7 @@ int bch2_dev_freespace_init(struct bch_fs *, struct bch_dev *, u64, u64);
 int bch2_fs_freespace_init(struct bch_fs *);
 
 void bch2_recalc_capacity(struct bch_fs *);
+u64 bch2_min_rw_member_capacity(struct bch_fs *);
 
 void bch2_dev_allocator_remove(struct bch_fs *, struct bch_dev *);
 void bch2_dev_allocator_add(struct bch_fs *, struct bch_dev *);

fs/bcachefs/movinggc.c

@@ -188,7 +188,8 @@ static int bch2_copygc_get_buckets(struct moving_context *ctxt,
 
 noinline
 static int bch2_copygc(struct moving_context *ctxt,
-		       struct buckets_in_flight *buckets_in_flight)
+		       struct buckets_in_flight *buckets_in_flight,
+		       bool *did_work)
 {
 	struct btree_trans *trans = ctxt->trans;
 	struct bch_fs *c = trans->c;
@@ -224,6 +225,8 @@ static int bch2_copygc(struct moving_context *ctxt,
 					     f->bucket.k.gen, data_opts);
 		if (ret)
 			goto err;
+
+		*did_work = true;
 	}
 err:
 	darray_exit(&buckets);
@@ -322,6 +325,8 @@ static int bch2_copygc_thread(void *arg)
 			      false);
 
 	while (!ret && !kthread_should_stop()) {
+		bool did_work = false;
+
 		bch2_trans_unlock(ctxt.trans);
 		cond_resched();
 
@@ -352,10 +357,21 @@ static int bch2_copygc_thread(void *arg)
 		c->copygc_wait = 0;
 
 		c->copygc_running = true;
-		ret = bch2_copygc(&ctxt, &buckets);
+		ret = bch2_copygc(&ctxt, &buckets, &did_work);
 		c->copygc_running = false;
 
 		wake_up(&c->copygc_running_wq);
+
+		if (!wait && !did_work) {
+			u64 min_member_capacity = bch2_min_rw_member_capacity(c);
+
+			if (min_member_capacity == U64_MAX)
+				min_member_capacity = 128 * 2048;
+
+			bch2_trans_unlock_long(ctxt.trans);
+			bch2_kthread_io_clock_wait(clock, last + (min_member_capacity >> 6),
+					MAX_SCHEDULE_TIMEOUT);
+		}
 	}
 
 	move_buckets_wait(&ctxt, &buckets, true);

fs/bcachefs/rebalance.c

 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "alloc_background.h"
 #include "alloc_foreground.h"
 #include "btree_iter.h"
 #include "btree_update.h"
@@ -282,15 +283,12 @@ static int do_rebalance_scan(struct moving_context *ctxt, u64 inum, u64 cookie)
 static void rebalance_wait(struct bch_fs *c)
 {
 	struct bch_fs_rebalance *r = &c->rebalance;
-	struct bch_dev *ca;
 	struct io_clock *clock = &c->io_clock[WRITE];
 	u64 now = atomic64_read(&clock->now);
-	u64 min_member_capacity = 128 * 2048;
-	unsigned i;
+	u64 min_member_capacity = bch2_min_rw_member_capacity(c);
 
-	for_each_rw_member(ca, c, i)
-		min_member_capacity = min(min_member_capacity,
-					  ca->mi.nbuckets * ca->mi.bucket_size);
+	if (min_member_capacity == U64_MAX)
+		min_member_capacity = 128 * 2048;
 
 	r->wait_iotime_end		= now + (min_member_capacity >> 6);