Btrfs: more efficient extent state insertions
Currently we do 2 traversals of an inode's extent_io_tree
before inserting an extent state structure: 1 to see if a
matching extent state already exists and 1 to do the insertion
if the fist traversal didn't found such extent state.
This change just combines those tree traversals into a single one.
While running sysbench tests (random writes) I captured the number
of elements in extent_io_tree trees for a while (into a procfs file
backed by a seq_list from seq_file module) and got this histogram:
Count: 9310
Range: 51.000 - 21386.000; Mean: 11785.243; Median: 18743.500; Stddev: 8923.688
Percentiles: 90th: 20985.000; 95th: 21155.000; 99th: 21369.000
51.000 - 93.933: 693 ########
93.933 - 172.314: 938 ##########
172.314 - 315.408: 856 #########
315.408 - 576.646: 95 #
576.646 - 6415.830: 888 ##########
6415.830 - 11713.809: 1024 ###########
11713.809 - 21386.000: 4816 #####################################################
So traversing such trees can take some significant time that can
easily be avoided.
Ran the following sysbench tests, 5 times each, for sequential and
random writes, and got the following results:
sysbench --test=fileio --file-num=1 --file-total-size=2G \
--file-test-mode=seqwr --num-threads=16 --file-block-size=65536 \
--max-requests=0 --max-time=60 --file-io-mode=sync
sysbench --test=fileio --file-num=1 --file-total-size=2G \
--file-test-mode=rndwr --num-threads=16 --file-block-size=65536 \
--max-requests=0 --max-time=60 --file-io-mode=sync
Before this change:
sequential writes: 69.28Mb/sec (average of 5 runs)
random writes: 4.14Mb/sec (average of 5 runs)
After this change:
sequential writes: 69.91Mb/sec (average of 5 runs)
random writes: 5.69Mb/sec (average of 5 runs)
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 01a1412..5fc9481 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -224,12 +224,20 @@
}
static struct rb_node *tree_insert(struct rb_root *root, u64 offset,
- struct rb_node *node)
+ struct rb_node *node,
+ struct rb_node ***p_in,
+ struct rb_node **parent_in)
{
struct rb_node **p = &root->rb_node;
struct rb_node *parent = NULL;
struct tree_entry *entry;
+ if (p_in && parent_in) {
+ p = *p_in;
+ parent = *parent_in;
+ goto do_insert;
+ }
+
while (*p) {
parent = *p;
entry = rb_entry(parent, struct tree_entry, rb_node);
@@ -242,35 +250,43 @@
return parent;
}
+do_insert:
rb_link_node(node, parent, p);
rb_insert_color(node, root);
return NULL;
}
static struct rb_node *__etree_search(struct extent_io_tree *tree, u64 offset,
- struct rb_node **prev_ret,
- struct rb_node **next_ret)
+ struct rb_node **prev_ret,
+ struct rb_node **next_ret,
+ struct rb_node ***p_ret,
+ struct rb_node **parent_ret)
{
struct rb_root *root = &tree->state;
- struct rb_node *n = root->rb_node;
+ struct rb_node **n = &root->rb_node;
struct rb_node *prev = NULL;
struct rb_node *orig_prev = NULL;
struct tree_entry *entry;
struct tree_entry *prev_entry = NULL;
- while (n) {
- entry = rb_entry(n, struct tree_entry, rb_node);
- prev = n;
+ while (*n) {
+ prev = *n;
+ entry = rb_entry(prev, struct tree_entry, rb_node);
prev_entry = entry;
if (offset < entry->start)
- n = n->rb_left;
+ n = &(*n)->rb_left;
else if (offset > entry->end)
- n = n->rb_right;
+ n = &(*n)->rb_right;
else
- return n;
+ return *n;
}
+ if (p_ret)
+ *p_ret = n;
+ if (parent_ret)
+ *parent_ret = prev;
+
if (prev_ret) {
orig_prev = prev;
while (prev && offset > prev_entry->end) {
@@ -292,18 +308,27 @@
return NULL;
}
-static inline struct rb_node *tree_search(struct extent_io_tree *tree,
- u64 offset)
+static inline struct rb_node *
+tree_search_for_insert(struct extent_io_tree *tree,
+ u64 offset,
+ struct rb_node ***p_ret,
+ struct rb_node **parent_ret)
{
struct rb_node *prev = NULL;
struct rb_node *ret;
- ret = __etree_search(tree, offset, &prev, NULL);
+ ret = __etree_search(tree, offset, &prev, NULL, p_ret, parent_ret);
if (!ret)
return prev;
return ret;
}
+static inline struct rb_node *tree_search(struct extent_io_tree *tree,
+ u64 offset)
+{
+ return tree_search_for_insert(tree, offset, NULL, NULL);
+}
+
static void merge_cb(struct extent_io_tree *tree, struct extent_state *new,
struct extent_state *other)
{
@@ -385,6 +410,8 @@
*/
static int insert_state(struct extent_io_tree *tree,
struct extent_state *state, u64 start, u64 end,
+ struct rb_node ***p,
+ struct rb_node **parent,
unsigned long *bits)
{
struct rb_node *node;
@@ -397,7 +424,7 @@
set_state_bits(tree, state, bits);
- node = tree_insert(&tree->state, end, &state->rb_node);
+ node = tree_insert(&tree->state, end, &state->rb_node, p, parent);
if (node) {
struct extent_state *found;
found = rb_entry(node, struct extent_state, rb_node);
@@ -444,7 +471,8 @@
prealloc->state = orig->state;
orig->start = split;
- node = tree_insert(&tree->state, prealloc->end, &prealloc->rb_node);
+ node = tree_insert(&tree->state, prealloc->end, &prealloc->rb_node,
+ NULL, NULL);
if (node) {
free_extent_state(prealloc);
return -EEXIST;
@@ -783,6 +811,8 @@
struct extent_state *state;
struct extent_state *prealloc = NULL;
struct rb_node *node;
+ struct rb_node **p;
+ struct rb_node *parent;
int err = 0;
u64 last_start;
u64 last_end;
@@ -809,11 +839,12 @@
* this search will find all the extents that end after
* our range starts.
*/
- node = tree_search(tree, start);
+ node = tree_search_for_insert(tree, start, &p, &parent);
if (!node) {
prealloc = alloc_extent_state_atomic(prealloc);
BUG_ON(!prealloc);
- err = insert_state(tree, prealloc, start, end, &bits);
+ err = insert_state(tree, prealloc, start, end,
+ &p, &parent, &bits);
if (err)
extent_io_tree_panic(tree, err);
@@ -920,7 +951,7 @@
* the later extent.
*/
err = insert_state(tree, prealloc, start, this_end,
- &bits);
+ NULL, NULL, &bits);
if (err)
extent_io_tree_panic(tree, err);
@@ -1006,6 +1037,8 @@
struct extent_state *state;
struct extent_state *prealloc = NULL;
struct rb_node *node;
+ struct rb_node **p;
+ struct rb_node *parent;
int err = 0;
u64 last_start;
u64 last_end;
@@ -1033,14 +1066,15 @@
* this search will find all the extents that end after
* our range starts.
*/
- node = tree_search(tree, start);
+ node = tree_search_for_insert(tree, start, &p, &parent);
if (!node) {
prealloc = alloc_extent_state_atomic(prealloc);
if (!prealloc) {
err = -ENOMEM;
goto out;
}
- err = insert_state(tree, prealloc, start, end, &bits);
+ err = insert_state(tree, prealloc, start, end,
+ &p, &parent, &bits);
if (err)
extent_io_tree_panic(tree, err);
cache_state(prealloc, cached_state);
@@ -1137,7 +1171,7 @@
* the later extent.
*/
err = insert_state(tree, prealloc, start, this_end,
- &bits);
+ NULL, NULL, &bits);
if (err)
extent_io_tree_panic(tree, err);
cache_state(prealloc, cached_state);