Btrfs: Change the congestion functions to meter the number of async submits as well

The async submit workqueue was absorbing too many requests, leading to long
stalls where the async submitters were stalling.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 264f297..3733743 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -453,6 +453,7 @@ int btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct inode *inode,
 
 	spin_lock(&fs_info->async_submit_work_lock);
 	list_add_tail(&async->list, &fs_info->async_submit_work_list);
+	atomic_inc(&fs_info->nr_async_submits);
 	spin_unlock(&fs_info->async_submit_work_lock);
 
 	queue_work(async_submit_workqueue, &fs_info->async_submit_work);
@@ -906,10 +907,16 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits)
 {
 	struct btrfs_fs_info *info = (struct btrfs_fs_info *)congested_data;
 	int ret = 0;
+	int limit = 256 * info->fs_devices->open_devices;
 	struct list_head *cur;
 	struct btrfs_device *device;
 	struct backing_dev_info *bdi;
 
+	if ((bdi_bits & (1 << BDI_write_congested)) &&
+	    atomic_read(&info->nr_async_submits) > limit) {
+		return 1;
+	}
+
 	list_for_each(cur, &info->fs_devices->devices) {
 		device = list_entry(cur, struct btrfs_device, dev_list);
 		if (!device->bdev)
@@ -1117,6 +1124,7 @@ static void btrfs_async_submit_work(struct work_struct *work)
 		}
 		next = fs_info->async_submit_work_list.next;
 		list_del(next);
+		atomic_dec(&fs_info->nr_async_submits);
 		spin_unlock(&fs_info->async_submit_work_lock);
 
 		async = list_entry(next, struct async_submit_bio, list);
@@ -1179,6 +1187,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
 	INIT_LIST_HEAD(&fs_info->space_info);
 	btrfs_mapping_init(&fs_info->mapping_tree);
+	atomic_set(&fs_info->nr_async_submits, 0);
 	fs_info->sb = sb;
 	fs_info->max_extent = (u64)-1;
 	fs_info->max_inline = 8192 * 1024;