[PATCH RFC 33/39] btrfs: qgroup: Introduce qgroup backref cache

[Qu Wenruo <wqu@xxxxxxxx>]

This adds two new members for btrfs_fs_info:
- struct backref_cache *qgroup_backref_cache
  Only get initialized at qgroup enable time.
  This is to avoid further bloating up fs_info structure.

- struct mutex qgroup_backref_lock
  This is initialized at fs_info initial time.

This patch only introduces the skeleton, just initialization and cleanup
for these newly introduced members, no usage of them yet.

Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
 fs/btrfs/ctree.h   |  2 ++
 fs/btrfs/disk-io.c |  1 +
 fs/btrfs/qgroup.c  | 51 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e45aad90b45e..6945754cca2a 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -889,6 +889,8 @@ struct btrfs_fs_info {
 	struct btrfs_workqueue *qgroup_rescan_workers;
 	struct completion qgroup_rescan_completion;
 	struct btrfs_work qgroup_rescan_work;
+	struct mutex qgroup_backref_lock;
+	struct backref_cache *qgroup_backref_cache;
 	bool qgroup_rescan_running;	/* protected by qgroup_rescan_lock */
 
 	/* filesystem state */
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 483b54077d01..67bb6fa5ab04 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2123,6 +2123,7 @@ static void btrfs_init_qgroup(struct btrfs_fs_info *fs_info)
 	fs_info->qgroup_ulist = NULL;
 	fs_info->qgroup_rescan_running = false;
 	mutex_init(&fs_info->qgroup_rescan_lock);
+	mutex_init(&fs_info->qgroup_backref_lock);
 }
 
 static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info,
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 75bc3b686498..3e628b5f1c39 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -339,6 +339,18 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
 	if (!test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags))
 		return 0;
 
+	mutex_lock(&fs_info->qgroup_backref_lock);
+	if (!fs_info->qgroup_backref_cache) {
+		fs_info->qgroup_backref_cache = kzalloc(
+				sizeof(struct backref_cache), GFP_KERNEL);
+		if (!fs_info->qgroup_backref_cache) {
+			mutex_unlock(&fs_info->qgroup_backref_lock);
+			return -ENOMEM;
+		}
+		backref_cache_init(fs_info, fs_info->qgroup_backref_cache, 0);
+	}
+	mutex_unlock(&fs_info->qgroup_backref_lock);
+
 	fs_info->qgroup_ulist = ulist_alloc(GFP_KERNEL);
 	if (!fs_info->qgroup_ulist) {
 		ret = -ENOMEM;
@@ -528,6 +540,14 @@ void btrfs_free_qgroup_config(struct btrfs_fs_info *fs_info)
 	 */
 	ulist_free(fs_info->qgroup_ulist);
 	fs_info->qgroup_ulist = NULL;
+
+	mutex_lock(&fs_info->qgroup_backref_lock);
+	if (fs_info->qgroup_backref_cache) {
+		backref_cache_release(fs_info->qgroup_backref_cache);
+		kfree(fs_info->qgroup_backref_cache);
+		fs_info->qgroup_backref_cache = NULL;
+	}
+	mutex_unlock(&fs_info->qgroup_backref_lock);
 }
 
 static int add_qgroup_relation_item(struct btrfs_trans_handle *trans, u64 src,
@@ -891,6 +911,19 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info)
 	int slot;
 
 	mutex_lock(&fs_info->qgroup_ioctl_lock);
+	mutex_lock(&fs_info->qgroup_backref_lock);
+	if (!fs_info->qgroup_backref_cache) {
+		fs_info->qgroup_backref_cache = kzalloc(
+				sizeof(struct backref_cache), GFP_KERNEL);
+		if (!fs_info->qgroup_backref_cache) {
+			mutex_unlock(&fs_info->qgroup_backref_lock);
+			ret = -ENOMEM;
+			goto out;
+		}
+		backref_cache_init(fs_info, fs_info->qgroup_backref_cache, 0);
+	}
+	mutex_unlock(&fs_info->qgroup_backref_lock);
+
 	if (fs_info->quota_root)
 		goto out;
 
@@ -1098,6 +1131,14 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info)
 		goto end_trans;
 	}
 
+	mutex_lock(&fs_info->qgroup_backref_lock);
+	if (fs_info->qgroup_backref_cache) {
+		backref_cache_release(fs_info->qgroup_backref_cache);
+		kfree(fs_info->qgroup_backref_cache);
+		fs_info->qgroup_backref_cache = NULL;
+	}
+	mutex_unlock(&fs_info->qgroup_backref_lock);
+
 	list_del(&quota_root->dirty_list);
 
 	btrfs_tree_lock(quota_root->node);
@@ -2566,6 +2607,16 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans)
 	}
 	trace_qgroup_num_dirty_extents(fs_info, trans->transid,
 				       num_dirty_extents);
+
+	/*
+	 * Qgroup accounting happens at commit transaction time, thus the
+	 * backref cache will no longer be valid in next trans.
+	 * Free it up.
+	 */
+	mutex_lock(&fs_info->qgroup_backref_lock);
+	if (fs_info->qgroup_backref_cache)
+		backref_cache_release(fs_info->qgroup_backref_cache);
+	mutex_unlock(&fs_info->qgroup_backref_lock);
 	return ret;
 }
 
-- 
2.25.1