Btrfs: Switch the extent buffer rbtree into a radix tree
This patch reduces the CPU time spent in the extent buffer search by using the
radix tree instead of the rbtree and using the rcu lock instead of the spin
lock.
I did a quick test by the benchmark tool[1] and found the patch improve the
file creation/deletion performance problem that I have reported[2].
Before applying this patch:
Create files:
Total files: 50000
Total time: 0.971531
Average time: 0.000019
Delete files:
Total files: 50000
Total time: 1.366761
Average time: 0.000027
After applying this patch:
Create files:
Total files: 50000
Total time: 0.927455
Average time: 0.000019
Delete files:
Total files: 50000
Total time: 1.292280
Average time: 0.000026
[1] http://marc.info/?l=linux-btrfs&m=128212635122920&q=p3
[2] http://marc.info/?l=linux-btrfs&m=128212635122920&w=2
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 6e3b326..4c639e1 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -104,7 +104,7 @@
struct address_space *mapping, gfp_t mask)
{
tree->state = RB_ROOT;
- tree->buffer = RB_ROOT;
+ INIT_RADIX_TREE(&tree->buffer, GFP_ATOMIC);
tree->ops = NULL;
tree->dirty_bytes = 0;
spin_lock_init(&tree->lock);
@@ -235,50 +235,6 @@
return ret;
}
-static struct extent_buffer *buffer_tree_insert(struct extent_io_tree *tree,
- u64 offset, struct rb_node *node)
-{
- struct rb_root *root = &tree->buffer;
- struct rb_node **p = &root->rb_node;
- struct rb_node *parent = NULL;
- struct extent_buffer *eb;
-
- while (*p) {
- parent = *p;
- eb = rb_entry(parent, struct extent_buffer, rb_node);
-
- if (offset < eb->start)
- p = &(*p)->rb_left;
- else if (offset > eb->start)
- p = &(*p)->rb_right;
- else
- return eb;
- }
-
- rb_link_node(node, parent, p);
- rb_insert_color(node, root);
- return NULL;
-}
-
-static struct extent_buffer *buffer_search(struct extent_io_tree *tree,
- u64 offset)
-{
- struct rb_root *root = &tree->buffer;
- struct rb_node *n = root->rb_node;
- struct extent_buffer *eb;
-
- while (n) {
- eb = rb_entry(n, struct extent_buffer, rb_node);
- if (offset < eb->start)
- n = n->rb_left;
- else if (offset > eb->start)
- n = n->rb_right;
- else
- return eb;
- }
- return NULL;
-}
-
static void merge_cb(struct extent_io_tree *tree, struct extent_state *new,
struct extent_state *other)
{
@@ -3082,6 +3038,7 @@
eb->len = len;
spin_lock_init(&eb->lock);
init_waitqueue_head(&eb->lock_wq);
+ INIT_RCU_HEAD(&eb->rcu_head);
#if LEAK_DEBUG
spin_lock_irqsave(&leak_lock, flags);
@@ -3150,16 +3107,16 @@
struct page *p;
struct address_space *mapping = tree->mapping;
int uptodate = 1;
+ int ret;
- spin_lock(&tree->buffer_lock);
- eb = buffer_search(tree, start);
- if (eb) {
- atomic_inc(&eb->refs);
- spin_unlock(&tree->buffer_lock);
+ rcu_read_lock();
+ eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+ if (eb && atomic_inc_not_zero(&eb->refs)) {
+ rcu_read_unlock();
mark_page_accessed(eb->first_page);
return eb;
}
- spin_unlock(&tree->buffer_lock);
+ rcu_read_unlock();
eb = __alloc_extent_buffer(tree, start, len, mask);
if (!eb)
@@ -3198,17 +3155,25 @@
if (uptodate)
set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+ ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
+ if (ret)
+ goto free_eb;
+
spin_lock(&tree->buffer_lock);
- exists = buffer_tree_insert(tree, start, &eb->rb_node);
- if (exists) {
+ ret = radix_tree_insert(&tree->buffer, start >> PAGE_CACHE_SHIFT, eb);
+ if (ret == -EEXIST) {
+ exists = radix_tree_lookup(&tree->buffer,
+ start >> PAGE_CACHE_SHIFT);
/* add one reference for the caller */
atomic_inc(&exists->refs);
spin_unlock(&tree->buffer_lock);
+ radix_tree_preload_end();
goto free_eb;
}
/* add one reference for the tree */
atomic_inc(&eb->refs);
spin_unlock(&tree->buffer_lock);
+ radix_tree_preload_end();
return eb;
free_eb:
@@ -3224,16 +3189,16 @@
{
struct extent_buffer *eb;
- spin_lock(&tree->buffer_lock);
- eb = buffer_search(tree, start);
- if (eb)
- atomic_inc(&eb->refs);
- spin_unlock(&tree->buffer_lock);
-
- if (eb)
+ rcu_read_lock();
+ eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
+ if (eb && atomic_inc_not_zero(&eb->refs)) {
+ rcu_read_unlock();
mark_page_accessed(eb->first_page);
+ return eb;
+ }
+ rcu_read_unlock();
- return eb;
+ return NULL;
}
void free_extent_buffer(struct extent_buffer *eb)
@@ -3863,6 +3828,14 @@
}
}
+static inline void btrfs_release_extent_buffer_rcu(struct rcu_head *head)
+{
+ struct extent_buffer *eb =
+ container_of(head, struct extent_buffer, rcu_head);
+
+ btrfs_release_extent_buffer(eb);
+}
+
int try_release_extent_buffer(struct extent_io_tree *tree, struct page *page)
{
u64 start = page_offset(page);
@@ -3870,23 +3843,30 @@
int ret = 1;
spin_lock(&tree->buffer_lock);
- eb = buffer_search(tree, start);
+ eb = radix_tree_lookup(&tree->buffer, start >> PAGE_CACHE_SHIFT);
if (!eb)
goto out;
- if (atomic_read(&eb->refs) > 1) {
- ret = 0;
- goto out;
- }
if (test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) {
ret = 0;
goto out;
}
- rb_erase(&eb->rb_node, &tree->buffer);
- /* at this point we can safely release the extent buffer */
- btrfs_release_extent_buffer(eb);
+ /*
+ * set @eb->refs to 0 if it is already 1, and then release the @eb.
+ * Or go back.
+ */
+ if (atomic_cmpxchg(&eb->refs, 1, 0) != 1) {
+ ret = 0;
+ goto out;
+ }
+
+ radix_tree_delete(&tree->buffer, start >> PAGE_CACHE_SHIFT);
out:
spin_unlock(&tree->buffer_lock);
+
+ /* at this point we can safely release the extent buffer */
+ if (atomic_read(&eb->refs) == 0)
+ call_rcu(&eb->rcu_head, btrfs_release_extent_buffer_rcu);
return ret;
}