btrfs: track refs in a rb_tree instead of a list
If we get a significant amount of delayed refs for a single block (think
modifying multiple snapshots) we can end up spending an ungodly amount
of time looping through all of the entries trying to see if they can be
merged. This is because we only add them to a list, so we have O(2n)
for every ref head. This doesn't make any sense as we likely have refs
for different roots, and so they cannot be merged. Tracking in a tree
will allow us to break as soon as we hit an entry that doesn't match,
making our worst case O(n).
With this we can also merge entries more easily. Before we had to hope
that matching refs were on the ends of our list, but with the tree we
can search down to exact matches and merge them at insert time.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 523d2db..7d0dc10 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -773,6 +773,7 @@
struct btrfs_key key;
struct btrfs_key tmp_op_key;
struct btrfs_key *op_key = NULL;
+ struct rb_node *n;
int count;
int ret = 0;
@@ -782,7 +783,9 @@
}
spin_lock(&head->lock);
- list_for_each_entry(node, &head->ref_list, list) {
+ for (n = rb_first(&head->ref_tree); n; n = rb_next(n)) {
+ node = rb_entry(n, struct btrfs_delayed_ref_node,
+ ref_node);
if (node->seq > seq)
continue;
diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index 8c7d7db..83be8f9 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -143,6 +143,34 @@
return NULL;
}
+static struct btrfs_delayed_ref_node* tree_insert(struct rb_root *root,
+ struct btrfs_delayed_ref_node *ins)
+{
+ struct rb_node **p = &root->rb_node;
+ struct rb_node *node = &ins->ref_node;
+ struct rb_node *parent_node = NULL;
+ struct btrfs_delayed_ref_node *entry;
+
+ while (*p) {
+ int comp;
+
+ parent_node = *p;
+ entry = rb_entry(parent_node, struct btrfs_delayed_ref_node,
+ ref_node);
+ comp = comp_refs(ins, entry, true);
+ if (comp < 0)
+ p = &(*p)->rb_left;
+ else if (comp > 0)
+ p = &(*p)->rb_right;
+ else
+ return entry;
+ }
+
+ rb_link_node(node, parent_node, p);
+ rb_insert_color(node, root);
+ return NULL;
+}
+
/*
* find an head entry based on bytenr. This returns the delayed ref
* head if it was able to find one, or NULL if nothing was in that spot.
@@ -212,7 +240,8 @@
struct btrfs_delayed_ref_node *ref)
{
assert_spin_locked(&head->lock);
- list_del(&ref->list);
+ rb_erase(&ref->ref_node, &head->ref_tree);
+ RB_CLEAR_NODE(&ref->ref_node);
if (!list_empty(&ref->add_list))
list_del(&ref->add_list);
ref->in_tree = 0;
@@ -229,24 +258,18 @@
u64 seq)
{
struct btrfs_delayed_ref_node *next;
+ struct rb_node *node = rb_next(&ref->ref_node);
bool done = false;
- next = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node,
- list);
- while (!done && &next->list != &head->ref_list) {
+ while (!done && node) {
int mod;
- struct btrfs_delayed_ref_node *next2;
- next2 = list_next_entry(next, list);
-
- if (next == ref)
- goto next;
-
+ next = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
+ node = rb_next(node);
if (seq && next->seq >= seq)
- goto next;
-
+ break;
if (comp_refs(ref, next, false))
- goto next;
+ break;
if (ref->action == next->action) {
mod = next->ref_mod;
@@ -270,8 +293,6 @@
WARN_ON(ref->type == BTRFS_TREE_BLOCK_REF_KEY ||
ref->type == BTRFS_SHARED_BLOCK_REF_KEY);
}
-next:
- next = next2;
}
return done;
@@ -283,11 +304,12 @@
struct btrfs_delayed_ref_head *head)
{
struct btrfs_delayed_ref_node *ref;
+ struct rb_node *node;
u64 seq = 0;
assert_spin_locked(&head->lock);
- if (list_empty(&head->ref_list))
+ if (RB_EMPTY_ROOT(&head->ref_tree))
return;
/* We don't have too many refs to merge for data. */
@@ -304,22 +326,13 @@
}
spin_unlock(&fs_info->tree_mod_seq_lock);
- ref = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node,
- list);
- while (&ref->list != &head->ref_list) {
+again:
+ for (node = rb_first(&head->ref_tree); node; node = rb_next(node)) {
+ ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
if (seq && ref->seq >= seq)
- goto next;
-
- if (merge_ref(trans, delayed_refs, head, ref, seq)) {
- if (list_empty(&head->ref_list))
- break;
- ref = list_first_entry(&head->ref_list,
- struct btrfs_delayed_ref_node,
- list);
continue;
- }
-next:
- ref = list_next_entry(ref, list);
+ if (merge_ref(trans, delayed_refs, head, ref, seq))
+ goto again;
}
}
@@ -402,25 +415,19 @@
* Return 0 for insert.
* Return >0 for merge.
*/
-static int
-add_delayed_ref_tail_merge(struct btrfs_trans_handle *trans,
- struct btrfs_delayed_ref_root *root,
- struct btrfs_delayed_ref_head *href,
- struct btrfs_delayed_ref_node *ref)
+static int insert_delayed_ref(struct btrfs_trans_handle *trans,
+ struct btrfs_delayed_ref_root *root,
+ struct btrfs_delayed_ref_head *href,
+ struct btrfs_delayed_ref_node *ref)
{
struct btrfs_delayed_ref_node *exist;
int mod;
int ret = 0;
spin_lock(&href->lock);
- /* Check whether we can merge the tail node with ref */
- if (list_empty(&href->ref_list))
- goto add_tail;
- exist = list_entry(href->ref_list.prev, struct btrfs_delayed_ref_node,
- list);
- /* No need to compare bytenr nor is_head */
- if (comp_refs(exist, ref, true))
- goto add_tail;
+ exist = tree_insert(&href->ref_tree, ref);
+ if (!exist)
+ goto inserted;
/* Now we are sure we can merge */
ret = 1;
@@ -451,9 +458,7 @@
drop_delayed_ref(trans, root, href, exist);
spin_unlock(&href->lock);
return ret;
-
-add_tail:
- list_add_tail(&ref->list, &href->ref_list);
+inserted:
if (ref->action == BTRFS_ADD_DELAYED_REF)
list_add_tail(&ref->add_list, &href->ref_add_list);
atomic_inc(&root->num_entries);
@@ -593,7 +598,7 @@
head_ref->ref_mod = count_mod;
head_ref->must_insert_reserved = must_insert_reserved;
head_ref->is_data = is_data;
- INIT_LIST_HEAD(&head_ref->ref_list);
+ head_ref->ref_tree = RB_ROOT;
INIT_LIST_HEAD(&head_ref->ref_add_list);
RB_CLEAR_NODE(&head_ref->href_node);
head_ref->processing = 0;
@@ -685,7 +690,7 @@
ref->is_head = 0;
ref->in_tree = 1;
ref->seq = seq;
- INIT_LIST_HEAD(&ref->list);
+ RB_CLEAR_NODE(&ref->ref_node);
INIT_LIST_HEAD(&ref->add_list);
full_ref = btrfs_delayed_node_to_tree_ref(ref);
@@ -699,7 +704,7 @@
trace_add_delayed_tree_ref(fs_info, ref, full_ref, action);
- ret = add_delayed_ref_tail_merge(trans, delayed_refs, head_ref, ref);
+ ret = insert_delayed_ref(trans, delayed_refs, head_ref, ref);
/*
* XXX: memory should be freed at the same level allocated.
@@ -742,7 +747,7 @@
ref->is_head = 0;
ref->in_tree = 1;
ref->seq = seq;
- INIT_LIST_HEAD(&ref->list);
+ RB_CLEAR_NODE(&ref->ref_node);
INIT_LIST_HEAD(&ref->add_list);
full_ref = btrfs_delayed_node_to_data_ref(ref);
@@ -758,8 +763,7 @@
trace_add_delayed_data_ref(fs_info, ref, full_ref, action);
- ret = add_delayed_ref_tail_merge(trans, delayed_refs, head_ref, ref);
-
+ ret = insert_delayed_ref(trans, delayed_refs, head_ref, ref);
if (ret > 0)
kmem_cache_free(btrfs_delayed_data_ref_cachep, full_ref);
}
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index 1ce1185..a43af43 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -27,8 +27,7 @@
#define BTRFS_UPDATE_DELAYED_HEAD 4 /* not changing ref count on head ref */
struct btrfs_delayed_ref_node {
- /*data/tree ref use list, stored in ref_head->ref_list. */
- struct list_head list;
+ struct rb_node ref_node;
/*
* If action is BTRFS_ADD_DELAYED_REF, also link this node to
* ref_head->ref_add_list, then we do not need to iterate the
@@ -92,7 +91,7 @@
struct mutex mutex;
spinlock_t lock;
- struct list_head ref_list;
+ struct rb_root ref_tree;
/* accumulate add BTRFS_ADD_DELAYED_REF nodes to this ref_add_list. */
struct list_head ref_add_list;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d1f396f..efce9a2 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -4113,7 +4113,7 @@
while ((node = rb_first(&delayed_refs->href_root)) != NULL) {
struct btrfs_delayed_ref_head *head;
- struct btrfs_delayed_ref_node *tmp;
+ struct rb_node *n;
bool pin_bytes = false;
head = rb_entry(node, struct btrfs_delayed_ref_head,
@@ -4129,10 +4129,12 @@
continue;
}
spin_lock(&head->lock);
- list_for_each_entry_safe_reverse(ref, tmp, &head->ref_list,
- list) {
+ while ((n = rb_first(&head->ref_tree)) != NULL) {
+ ref = rb_entry(n, struct btrfs_delayed_ref_node,
+ ref_node);
ref->in_tree = 0;
- list_del(&ref->list);
+ rb_erase(&ref->ref_node, &head->ref_tree);
+ RB_CLEAR_NODE(&ref->ref_node);
if (!list_empty(&ref->add_list))
list_del(&ref->add_list);
atomic_dec(&delayed_refs->num_entries);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index fc9720e..673ac4e 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2519,7 +2519,7 @@
{
struct btrfs_delayed_ref_node *ref;
- if (list_empty(&head->ref_list))
+ if (RB_EMPTY_ROOT(&head->ref_tree))
return NULL;
/*
@@ -2532,8 +2532,8 @@
return list_first_entry(&head->ref_add_list,
struct btrfs_delayed_ref_node, add_list);
- ref = list_first_entry(&head->ref_list, struct btrfs_delayed_ref_node,
- list);
+ ref = rb_entry(rb_first(&head->ref_tree),
+ struct btrfs_delayed_ref_node, ref_node);
ASSERT(list_empty(&ref->add_list));
return ref;
}
@@ -2593,7 +2593,7 @@
spin_unlock(&head->lock);
spin_lock(&delayed_refs->lock);
spin_lock(&head->lock);
- if (!list_empty(&head->ref_list) || head->extent_op) {
+ if (!RB_EMPTY_ROOT(&head->ref_tree) || head->extent_op) {
spin_unlock(&head->lock);
spin_unlock(&delayed_refs->lock);
return 1;
@@ -2740,7 +2740,8 @@
actual_count++;
ref->in_tree = 0;
- list_del(&ref->list);
+ rb_erase(&ref->ref_node, &locked_ref->ref_tree);
+ RB_CLEAR_NODE(&ref->ref_node);
if (!list_empty(&ref->add_list))
list_del(&ref->add_list);
/*
@@ -3138,6 +3139,7 @@
struct btrfs_delayed_data_ref *data_ref;
struct btrfs_delayed_ref_root *delayed_refs;
struct btrfs_transaction *cur_trans;
+ struct rb_node *node;
int ret = 0;
cur_trans = root->fs_info->running_transaction;
@@ -3170,7 +3172,12 @@
spin_unlock(&delayed_refs->lock);
spin_lock(&head->lock);
- list_for_each_entry(ref, &head->ref_list, list) {
+ /*
+ * XXX: We should replace this with a proper search function in the
+ * future.
+ */
+ for (node = rb_first(&head->ref_tree); node; node = rb_next(node)) {
+ ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
/* If it's a shared ref we know a cross reference exists */
if (ref->type != BTRFS_EXTENT_DATA_REF_KEY) {
ret = 1;
@@ -7141,7 +7148,7 @@
goto out_delayed_unlock;
spin_lock(&head->lock);
- if (!list_empty(&head->ref_list))
+ if (!RB_EMPTY_ROOT(&head->ref_tree))
goto out;
if (head->extent_op) {