[PATCH v2] btrfs: qgroup: use xarray to track dirty extents in transaction.

[Junchao Sun <sunjunchao2870@gmail.com>]

Changes since v1:
 - Use xa_load() to update existing entry instead of double
   xa_store().
 - Rename goto lables.
 - Remove unnecessary calls to xa_init().

Using xarray to track dirty extents can reduce the size of the
struct btrfs_qgroup_extent_record from 64 bytes to 40 bytes.
And xarray is more cache line friendly, it also reduces the
complexity of insertion and search code compared to rb tree.

Another change introduced is about error handling.
Before this patch, the result of btrfs_qgroup_trace_extent_nolock()
is always a success. In this patch, because of this function calls
the function xa_store() which has the possibility to fail, so mark
qgroup as inconsistent if error happened and then free preallocated
memory. Also we preallocate memory before spin_lock(), if memory
preallcation failed, error handling is the same the existing code.

This patch passed the check -g qgroup tests using xfstests and
checkpatch tests.

Suggested-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Junchao Sun <sunjunchao2870@gmail.com>
---
 fs/btrfs/delayed-ref.c | 57 ++++++++++++++++++++--------------
 fs/btrfs/delayed-ref.h |  2 +-
 fs/btrfs/qgroup.c      | 69 +++++++++++++++++++++---------------------
 fs/btrfs/qgroup.h      |  1 -
 fs/btrfs/transaction.c |  6 ++--
 5 files changed, 73 insertions(+), 62 deletions(-)

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index 891ea2fa263c..e5cbc91e9864 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -915,8 +915,11 @@ add_delayed_ref_head(struct btrfs_trans_handle *trans,
 	/* Record qgroup extent info if provided */
 	if (qrecord) {
 		if (btrfs_qgroup_trace_extent_nolock(trans->fs_info,
-					delayed_refs, qrecord))
+					delayed_refs, qrecord)) {
+			/* If insertion failed, free preallocated memory */
+			xa_release(&delayed_refs->dirty_extents, qrecord->bytenr);
 			kfree(qrecord);
+		}
 		else
 			qrecord_inserted = true;
 	}
@@ -1029,6 +1032,7 @@ int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
 	u8 ref_type;
 
 	is_system = (generic_ref->tree_ref.ref_root == BTRFS_CHUNK_TREE_OBJECTID);
+	delayed_refs = &trans->transaction->delayed_refs;
 
 	ASSERT(generic_ref->type == BTRFS_REF_METADATA && generic_ref->action);
 	ref = kmem_cache_alloc(btrfs_delayed_tree_ref_cachep, GFP_NOFS);
@@ -1036,18 +1040,15 @@ int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 
 	head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep, GFP_NOFS);
-	if (!head_ref) {
-		kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
-		return -ENOMEM;
-	}
+	if (!head_ref)
+		goto free_ref;
 
 	if (btrfs_qgroup_full_accounting(fs_info) && !generic_ref->skip_qgroup) {
 		record = kzalloc(sizeof(*record), GFP_NOFS);
-		if (!record) {
-			kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
-			kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
-			return -ENOMEM;
-		}
+		if (!record)
+			goto free_head_ref;
+		if (xa_reserve(&delayed_refs->dirty_extents, bytenr, GFP_NOFS))
+			goto free_record;
 	}
 
 	if (parent)
@@ -1067,7 +1068,6 @@ int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
 			      false, is_system, generic_ref->owning_root);
 	head_ref->extent_op = extent_op;
 
-	delayed_refs = &trans->transaction->delayed_refs;
 	spin_lock(&delayed_refs->lock);
 
 	/*
@@ -1096,6 +1096,14 @@ int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
 		btrfs_qgroup_trace_extent_post(trans, record);
 
 	return 0;
+
+free_record:
+	kfree(record);
+free_head_ref:
+	kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
+free_ref:
+	kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
+	return -ENOMEM;
 }
 
 /*
@@ -1137,28 +1145,23 @@ int btrfs_add_delayed_data_ref(struct btrfs_trans_handle *trans,
 	ref->objectid = owner;
 	ref->offset = offset;
 
-
+	delayed_refs = &trans->transaction->delayed_refs;
 	head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep, GFP_NOFS);
-	if (!head_ref) {
-		kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
-		return -ENOMEM;
-	}
+	if (!head_ref)
+		goto free_ref;
 
 	if (btrfs_qgroup_full_accounting(fs_info) && !generic_ref->skip_qgroup) {
 		record = kzalloc(sizeof(*record), GFP_NOFS);
-		if (!record) {
-			kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
-			kmem_cache_free(btrfs_delayed_ref_head_cachep,
-					head_ref);
-			return -ENOMEM;
-		}
+		if (!record)
+			goto free_head_ref;
+		if (xa_reserve(&delayed_refs->dirty_extents, bytenr, GFP_NOFS))
+			goto free_record;
 	}
 
 	init_delayed_ref_head(head_ref, record, bytenr, num_bytes, ref_root,
 			      reserved, action, true, false, generic_ref->owning_root);
 	head_ref->extent_op = NULL;
 
-	delayed_refs = &trans->transaction->delayed_refs;
 	spin_lock(&delayed_refs->lock);
 
 	/*
@@ -1187,6 +1190,14 @@ int btrfs_add_delayed_data_ref(struct btrfs_trans_handle *trans,
 	if (qrecord_inserted)
 		return btrfs_qgroup_trace_extent_post(trans, record);
 	return 0;
+
+free_record:
+	kfree(record);
+free_head_ref:
+	kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
+free_ref:
+	kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
+	return -ENOMEM;
 }
 
 int btrfs_add_delayed_extent_op(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index 62d679d40f4f..f9b20c0671c7 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -166,7 +166,7 @@ struct btrfs_delayed_ref_root {
 	struct rb_root_cached href_root;
 
 	/* dirty extent records */
-	struct rb_root dirty_extent_root;
+	struct xarray dirty_extents;
 
 	/* this spin lock protects the rbtree and the entries inside */
 	spinlock_t lock;
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 5470e1cdf10c..717e16da9679 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1890,16 +1890,13 @@ int btrfs_limit_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid,
  *
  * Return 0 for success insert
  * Return >0 for existing record, caller can free @record safely.
- * Error is not possible
  */
 int btrfs_qgroup_trace_extent_nolock(struct btrfs_fs_info *fs_info,
 				struct btrfs_delayed_ref_root *delayed_refs,
 				struct btrfs_qgroup_extent_record *record)
 {
-	struct rb_node **p = &delayed_refs->dirty_extent_root.rb_node;
-	struct rb_node *parent_node = NULL;
-	struct btrfs_qgroup_extent_record *entry;
-	u64 bytenr = record->bytenr;
+	struct btrfs_qgroup_extent_record *existing, *ret;
+	unsigned long bytenr = record->bytenr;
 
 	if (!btrfs_qgroup_full_accounting(fs_info))
 		return 1;
@@ -1907,26 +1904,27 @@ int btrfs_qgroup_trace_extent_nolock(struct btrfs_fs_info *fs_info,
 	lockdep_assert_held(&delayed_refs->lock);
 	trace_btrfs_qgroup_trace_extent(fs_info, record);
 
-	while (*p) {
-		parent_node = *p;
-		entry = rb_entry(parent_node, struct btrfs_qgroup_extent_record,
-				 node);
-		if (bytenr < entry->bytenr) {
-			p = &(*p)->rb_left;
-		} else if (bytenr > entry->bytenr) {
-			p = &(*p)->rb_right;
-		} else {
-			if (record->data_rsv && !entry->data_rsv) {
-				entry->data_rsv = record->data_rsv;
-				entry->data_rsv_refroot =
-					record->data_rsv_refroot;
-			}
-			return 1;
+	xa_lock(&delayed_refs->dirty_extents);
+	existing = xa_load(&delayed_refs->dirty_extents, bytenr);
+	if (existing) {
+		if (record->data_rsv && !existing->data_rsv) {
+			existing->data_rsv = record->data_rsv;
+			existing->data_rsv_refroot = record->data_rsv_refroot;
 		}
+		xa_unlock(&delayed_refs->dirty_extents);
+		return 1;
+	}
+
+	ret = __xa_store(&delayed_refs->dirty_extents, record->bytenr, record, GFP_ATOMIC);
+	xa_unlock(&delayed_refs->dirty_extents);
+	if (xa_is_err(ret)) {
+		spin_lock(&fs_info->qgroup_lock);
+		fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
+		spin_unlock(&fs_info->qgroup_lock);
+
+		return 1;
 	}
 
-	rb_link_node(&record->node, parent_node, p);
-	rb_insert_color(&record->node, &delayed_refs->dirty_extent_root);
 	return 0;
 }
 
@@ -2027,13 +2025,18 @@ int btrfs_qgroup_trace_extent(struct btrfs_trans_handle *trans, u64 bytenr,
 	struct btrfs_delayed_ref_root *delayed_refs;
 	int ret;
 
+	delayed_refs = &trans->transaction->delayed_refs;
 	if (!btrfs_qgroup_full_accounting(fs_info) || bytenr == 0 || num_bytes == 0)
 		return 0;
 	record = kzalloc(sizeof(*record), GFP_NOFS);
 	if (!record)
 		return -ENOMEM;
 
-	delayed_refs = &trans->transaction->delayed_refs;
+	if (xa_reserve(&delayed_refs->dirty_extents, bytenr, GFP_NOFS)) {
+		kfree(record);
+		return -ENOMEM;
+	}
+
 	record->bytenr = bytenr;
 	record->num_bytes = num_bytes;
 	record->old_roots = NULL;
@@ -2042,9 +2045,12 @@ int btrfs_qgroup_trace_extent(struct btrfs_trans_handle *trans, u64 bytenr,
 	ret = btrfs_qgroup_trace_extent_nolock(fs_info, delayed_refs, record);
 	spin_unlock(&delayed_refs->lock);
 	if (ret > 0) {
+		/* If insertion failed, free preallocated memory */
+		xa_release(&delayed_refs->dirty_extents, record->bytenr);
 		kfree(record);
 		return 0;
 	}
+
 	return btrfs_qgroup_trace_extent_post(trans, record);
 }
 
@@ -2912,7 +2918,7 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans)
 	struct btrfs_qgroup_extent_record *record;
 	struct btrfs_delayed_ref_root *delayed_refs;
 	struct ulist *new_roots = NULL;
-	struct rb_node *node;
+	unsigned long index;
 	u64 num_dirty_extents = 0;
 	u64 qgroup_to_skip;
 	int ret = 0;
@@ -2922,10 +2928,7 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans)
 
 	delayed_refs = &trans->transaction->delayed_refs;
 	qgroup_to_skip = delayed_refs->qgroup_to_skip;
-	while ((node = rb_first(&delayed_refs->dirty_extent_root))) {
-		record = rb_entry(node, struct btrfs_qgroup_extent_record,
-				  node);
-
+	xa_for_each(&delayed_refs->dirty_extents, index, record) {
 		num_dirty_extents++;
 		trace_btrfs_qgroup_account_extents(fs_info, record);
 
@@ -2991,7 +2994,7 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans)
 		ulist_free(record->old_roots);
 		ulist_free(new_roots);
 		new_roots = NULL;
-		rb_erase(node, &delayed_refs->dirty_extent_root);
+		xa_erase(&delayed_refs->dirty_extents, index);
 		kfree(record);
 
 	}
@@ -4664,15 +4667,13 @@ int btrfs_qgroup_trace_subtree_after_cow(struct btrfs_trans_handle *trans,
 void btrfs_qgroup_destroy_extent_records(struct btrfs_transaction *trans)
 {
 	struct btrfs_qgroup_extent_record *entry;
-	struct btrfs_qgroup_extent_record *next;
-	struct rb_root *root;
+	unsigned long index;
 
-	root = &trans->delayed_refs.dirty_extent_root;
-	rbtree_postorder_for_each_entry_safe(entry, next, root, node) {
+	xa_for_each(&trans->delayed_refs.dirty_extents, index, entry) {
 		ulist_free(entry->old_roots);
 		kfree(entry);
 	}
-	*root = RB_ROOT;
+	xa_destroy(&trans->delayed_refs.dirty_extents);
 }
 
 void btrfs_free_squota_rsv(struct btrfs_fs_info *fs_info, u64 root, u64 rsv_bytes)
diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
index be18c862e64e..f8165a27b885 100644
--- a/fs/btrfs/qgroup.h
+++ b/fs/btrfs/qgroup.h
@@ -116,7 +116,6 @@
  * TODO: Use kmem cache to alloc it.
  */
 struct btrfs_qgroup_extent_record {
-	struct rb_node node;
 	u64 bytenr;
 	u64 num_bytes;
 
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index bf8e64c766b6..22e917f47452 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -145,8 +145,8 @@ void btrfs_put_transaction(struct btrfs_transaction *transaction)
 		BUG_ON(!list_empty(&transaction->list));
 		WARN_ON(!RB_EMPTY_ROOT(
 				&transaction->delayed_refs.href_root.rb_root));
-		WARN_ON(!RB_EMPTY_ROOT(
-				&transaction->delayed_refs.dirty_extent_root));
+		WARN_ON(!xa_empty(
+				&transaction->delayed_refs.dirty_extents));
 		if (transaction->delayed_refs.pending_csums)
 			btrfs_err(transaction->fs_info,
 				  "pending csums is %llu",
@@ -353,7 +353,7 @@ static noinline int join_transaction(struct btrfs_fs_info *fs_info,
 	memset(&cur_trans->delayed_refs, 0, sizeof(cur_trans->delayed_refs));
 
 	cur_trans->delayed_refs.href_root = RB_ROOT_CACHED;
-	cur_trans->delayed_refs.dirty_extent_root = RB_ROOT;
+	xa_init(&cur_trans->delayed_refs.dirty_extents);
 	atomic_set(&cur_trans->delayed_refs.num_entries, 0);
 
 	/*
-- 
2.39.2