Commit 80db4e47 authored by Coly Li's avatar Coly Li Committed by Jens Axboe
Browse files

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: default avatarColy Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-4-colyli@suse.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4dc34ae1

drivers/md/bcache/writeback.c

+13 −28
Original line number Diff line number Diff line
@@ -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;

	}