Btrfs: Throttle operations if the reference cache gets too large

A large reference cache is directly related to a lot of work pending
for the cleaner thread.  This throttles back new operations based on
the size of the reference cache so the cleaner thread will be able to keep
up.

Overall, this actually makes the FS faster because the cleaner thread will
be more likely to find things in cache.

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

7 files changed, 58 insertions, 22 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4eca0aa1ce7..5517dfc6f71 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -580,6 +580,7 @@ struct btrfs_fs_info {
 	int do_barriers;
 	int closing;
 	atomic_t throttles;
+	atomic_t throttle_gen;
 
 	u64 total_pinned;
 	struct list_head dirty_cowonly_roots;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index eccdf13a95a..27ffa9b7ddc 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1171,8 +1171,10 @@ static int transaction_kthread(void *arg)
 		vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);
 		mutex_lock(&root->fs_info->transaction_kthread_mutex);
 
-		printk("btrfs: total reference cache size %Lu\n",
-			root->fs_info->total_ref_cache_size);
+		if (root->fs_info->total_ref_cache_size > 20 * 1024 * 1024) {
+			printk("btrfs: total reference cache size %Lu\n",
+				root->fs_info->total_ref_cache_size);
+		}
 
 		mutex_lock(&root->fs_info->trans_mutex);
 		cur = root->fs_info->running_transaction;
@@ -1256,6 +1258,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	btrfs_mapping_init(&fs_info->mapping_tree);
 	atomic_set(&fs_info->nr_async_submits, 0);
 	atomic_set(&fs_info->throttles, 0);
+	atomic_set(&fs_info->throttle_gen, 0);
 	fs_info->sb = sb;
 	fs_info->max_extent = (u64)-1;
 	fs_info->max_inline = 8192 * 1024;
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0e294cfaa60..6290cf41d64 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2650,6 +2650,7 @@ int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 		}
 	}
 	while(1) {
+		atomic_inc(&root->fs_info->throttle_gen);
 		wret = walk_down_tree(trans, root, path, &level);
 		if (wret > 0)
 			break;
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 3efec25e34b..ded5281f846 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -974,6 +974,7 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
 		balance_dirty_pages_ratelimited_nr(inode->i_mapping, num_pages);
 		if (num_pages < (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
 			btrfs_btree_balance_dirty(root, 1);
+		btrfs_throttle(root);
 		cond_resched();
 	}
 out:
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4f977ea5497..7c87f863d6f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2482,7 +2482,7 @@ static int btrfs_create(struct inode *dir, struct dentry *dentry,
 	btrfs_update_inode_block_group(trans, dir);
 out_unlock:
 	nr = trans->blocks_used;
-	btrfs_end_transaction(trans, root);
+	btrfs_end_transaction_throttle(trans, root);
 fail:
 	if (drop_inode) {
 		inode_dec_link_count(inode);
@@ -2535,7 +2535,7 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
 		drop_inode = 1;
 
 	nr = trans->blocks_used;
-	btrfs_end_transaction(trans, root);
+	btrfs_end_transaction_throttle(trans, root);
 fail:
 	if (drop_inode) {
 		inode_dec_link_count(inode);
@@ -2609,7 +2609,7 @@ static int btrfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 
 out_fail:
 	nr = trans->blocks_used;
-	btrfs_end_transaction(trans, root);
+	btrfs_end_transaction_throttle(trans, root);
 
 out_unlock:
 	if (drop_on_err)
@@ -3434,7 +3434,7 @@ static int btrfs_rename(struct inode * old_dir, struct dentry *old_dentry,
 		goto out_fail;
 
 out_fail:
-	btrfs_end_transaction(trans, root);
+	btrfs_end_transaction_throttle(trans, root);
 out_unlock:
 	return ret;
 }
@@ -3548,7 +3548,7 @@ static int btrfs_symlink(struct inode *dir, struct dentry *dentry,
 
 out_unlock:
 	nr = trans->blocks_used;
-	btrfs_end_transaction(trans, root);
+	btrfs_end_transaction_throttle(trans, root);
 out_fail:
 	if (drop_inode) {
 		inode_dec_link_count(inode);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index fcef3cae0c9..b8be6703189 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -202,35 +202,64 @@ static noinline int wait_for_commit(struct btrfs_root *root,
 	return 0;
 }
 
+void btrfs_throttle(struct btrfs_root *root)
+{
+	struct btrfs_fs_info *info = root->fs_info;
+
+harder:
+	if (atomic_read(&info->throttles)) {
+		DEFINE_WAIT(wait);
+		int thr;
+		int harder_count = 0;
+		thr = atomic_read(&info->throttle_gen);
+
+		do {
+			prepare_to_wait(&info->transaction_throttle,
+					&wait, TASK_UNINTERRUPTIBLE);
+			if (!atomic_read(&info->throttles)) {
+				finish_wait(&info->transaction_throttle, &wait);
+				break;
+			}
+			schedule();
+			finish_wait(&info->transaction_throttle, &wait);
+		} while (thr == atomic_read(&info->throttle_gen));
+
+		if (harder_count < 5 &&
+		    info->total_ref_cache_size > 5 * 1024 * 1024) {
+			harder_count++;
+			goto harder;
+		}
+
+		if (harder_count < 10 &&
+		    info->total_ref_cache_size > 10 * 1024 * 1024) {
+			harder_count++;
+			goto harder;
+		}
+	}
+}
+
 static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 			  struct btrfs_root *root, int throttle)
 {
 	struct btrfs_transaction *cur_trans;
+	struct btrfs_fs_info *info = root->fs_info;
 
-	mutex_lock(&root->fs_info->trans_mutex);
-	cur_trans = root->fs_info->running_transaction;
+	mutex_lock(&info->trans_mutex);
+	cur_trans = info->running_transaction;
 	WARN_ON(cur_trans != trans->transaction);
 	WARN_ON(cur_trans->num_writers < 1);
 	cur_trans->num_writers--;
 
 	if (waitqueue_active(&cur_trans->writer_wait))
 		wake_up(&cur_trans->writer_wait);
-
-	if (throttle && atomic_read(&root->fs_info->throttles)) {
-		DEFINE_WAIT(wait);
-		mutex_unlock(&root->fs_info->trans_mutex);
-		prepare_to_wait(&root->fs_info->transaction_throttle, &wait,
-				TASK_UNINTERRUPTIBLE);
-		if (atomic_read(&root->fs_info->throttles))
-			schedule();
-		finish_wait(&root->fs_info->transaction_throttle, &wait);
-		mutex_lock(&root->fs_info->trans_mutex);
-	}
-
 	put_transaction(cur_trans);
-	mutex_unlock(&root->fs_info->trans_mutex);
+	mutex_unlock(&info->trans_mutex);
 	memset(trans, 0, sizeof(*trans));
 	kmem_cache_free(btrfs_trans_handle_cachep, trans);
+
+	if (throttle)
+		btrfs_throttle(root);
+
 	return 0;
 }
 
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 11fbdeceb26..df2ca2aad1c 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -91,4 +91,5 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root);
 int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
 				   struct btrfs_root *root);
+void btrfs_throttle(struct btrfs_root *root);
 #endif