bcache: remove incremental dirty sector counting for bch_sectors_dirty_init()

After making bch_sectors_dirty_init() being multithreaded, the existing
incremental dirty sector counting in bch_root_node_dirty_init() doesn't
release btree occupation after iterating 500000 (INIT_KEYS_EACH_TIME)
bkeys. Because a read lock is added on btree root node to prevent the
btree to be split during the dirty sectors counting, other I/O requester
has no chance to gain the write lock even restart bcache_btree().

That is to say, the incremental dirty sectors counting is incompatible
to the multhreaded bch_sectors_dirty_init(). We have to choose one and
drop another one.

In my testing, with 512 bytes random writes, I generate 1.2T dirty data
and a btree with 400K nodes. With single thread and incremental dirty
sectors counting, it takes 30+ minites to register the backing device.
And with multithreaded dirty sectors counting, the backing device
registration can be accomplished within 2 minutes.

The 30+ minutes V.S. 2- minutes difference makes me decide to keep
multithreaded bch_sectors_dirty_init() and drop the incremental dirty
sectors counting. This is what this patch does.

But INIT_KEYS_EACH_TIME is kept, in sectors_dirty_init_fn() the CPU
will be released by cond_resched() after every INIT_KEYS_EACH_TIME keys
iterated. This is to avoid the watchdog reports a bogus soft lockup
warning.

Fixes: b144e45f ("bcache: make bch_sectors_dirty_init() to be multithreaded")
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-4-colyli@suse.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/writeback.c

@@ -805,13 +805,11 @@ static int bch_writeback_thread(void *arg)
 
 /* Init */
 #define INIT_KEYS_EACH_TIME	500000
-#define INIT_KEYS_SLEEP_MS	100
 
 struct sectors_dirty_init {
 	struct btree_op	op;
 	unsigned int	inode;
 	size_t		count;
-	struct bkey	start;
 };
 
 static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
@@ -827,11 +825,8 @@ static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
 					     KEY_START(k), KEY_SIZE(k));
 
 	op->count++;
-	if (atomic_read(&b->c->search_inflight) &&
-	    !(op->count % INIT_KEYS_EACH_TIME)) {
-		bkey_copy_key(&op->start, k);
-		return -EAGAIN;
-	}
+	if (!(op->count % INIT_KEYS_EACH_TIME))
+		cond_resched();
 
 	return MAP_CONTINUE;
 }
@@ -846,24 +841,16 @@ static int bch_root_node_dirty_init(struct cache_set *c,
 	bch_btree_op_init(&op.op, -1);
 	op.inode = d->id;
 	op.count = 0;
-	op.start = KEY(op.inode, 0, 0);
 
-	do {
 	ret = bcache_btree(map_keys_recurse,
 			   k,
 			   c->root,
 			   &op.op,
-				   &op.start,
+			   &KEY(op.inode, 0, 0),
 			   sectors_dirty_init_fn,
 			   0);
-		if (ret == -EAGAIN)
-			schedule_timeout_interruptible(
-				msecs_to_jiffies(INIT_KEYS_SLEEP_MS));
-		else if (ret < 0) {
+	if (ret < 0)
 		pr_warn("sectors dirty init failed, ret=%d!\n", ret);
-			break;
-		}
-	} while (ret == -EAGAIN);
 
 	return ret;
 }
@@ -907,7 +894,6 @@ static int bch_dirty_init_thread(void *arg)
 				goto out;
 			}
 			skip_nr--;
-			cond_resched();
 		}
 
 		if (p) {
@@ -917,7 +903,6 @@ static int bch_dirty_init_thread(void *arg)
 
 		p = NULL;
 		prev_idx = cur_idx;
-		cond_resched();
 	}
 
 out:
@@ -956,11 +941,11 @@ void bch_sectors_dirty_init(struct bcache_device *d)
 		bch_btree_op_init(&op.op, -1);
 		op.inode = d->id;
 		op.count = 0;
-		op.start = KEY(op.inode, 0, 0);
 
 		for_each_key_filter(&c->root->keys,
 				    k, &iter, bch_ptr_invalid)
 			sectors_dirty_init_fn(&op.op, c->root, k);
+
 		rw_unlock(0, c->root);
 		return;
 	}