Btrfs: cache extent state when writing out dirty metadata pages

Everytime we write out dirty pages we search for an offset in the tree,
convert the bits in the state, and then when we wait we search for the
offset again and clear the bits.  So for every dirty range in the io tree we
are doing 4 rb searches, which is suboptimal.  With this patch we are only
doing 2 searches for every cycle (modulo weird things happening).  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 41 insertions, 2 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 979fa0d6bfee..e8ee39b73356 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -937,6 +937,7 @@ int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, int bits,
  * @end:        the end offset in bytes (inclusive)
  * @bits:       the bits to set in this range
  * @clear_bits: the bits to clear in this range
+ * @cached_state:       state that we're going to cache
  * @mask:       the allocation mask
  *
  * This will go through and set bits for the given range.  If any states exist
@@ -946,7 +947,8 @@ int set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, int bits,
  * boundary bits like LOCK.
  */
 int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
-                       int bits, int clear_bits, gfp_t mask)
+                       int bits, int clear_bits,
+                       struct extent_state **cached_state, gfp_t mask)
 {
         struct extent_state *state;
         struct extent_state *prealloc = NULL;
@@ -963,6 +965,15 @@ again:
         }
 
         spin_lock(&tree->lock);
+        if (cached_state && *cached_state) {
+                state = *cached_state;
+                if (state->start <= start && state->end > start &&
+                    state->tree) {
+                        node = &state->rb_node;
+                        goto hit_next;
+                }
+        }
+
         /*
          * this search will find all the extents that end after
          * our range starts.
@@ -993,6 +1004,7 @@ hit_next:
          */
         if (state->start == start && state->end <= end) {
                 set_state_bits(tree, state, &bits);
+                cache_state(state, cached_state);
                 state = clear_state_bit(tree, state, &clear_bits, 0);
                 if (last_end == (u64)-1)
                         goto out;
@@ -1033,6 +1045,7 @@ hit_next:
                         goto out;
                 if (state->end <= end) {
                         set_state_bits(tree, state, &bits);
+                        cache_state(state, cached_state);
                         state = clear_state_bit(tree, state, &clear_bits, 0);
                         if (last_end == (u64)-1)
                                 goto out;
@@ -1071,6 +1084,7 @@ hit_next:
                                    &bits);
                 if (err)
                         extent_io_tree_panic(tree, err);
+                cache_state(prealloc, cached_state);
                 prealloc = NULL;
                 start = this_end + 1;
                 goto search_again;
@@ -1093,6 +1107,7 @@ hit_next:
                         extent_io_tree_panic(tree, err);
 
                 set_state_bits(tree, prealloc, &bits);
+                cache_state(prealloc, cached_state);
                 clear_state_bit(tree, prealloc, &clear_bits, 0);
                 prealloc = NULL;
                 goto out;
@@ -1297,18 +1312,42 @@ out:
  * If nothing was found, 1 is returned. If found something, return 0.
  */
 int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
-                          u64 *start_ret, u64 *end_ret, int bits)
+                          u64 *start_ret, u64 *end_ret, int bits,
+                          struct extent_state **cached_state)
 {
         struct extent_state *state;
+        struct rb_node *n;
         int ret = 1;
 
         spin_lock(&tree->lock);
+        if (cached_state && *cached_state) {
+                state = *cached_state;
+                if (state->end == start - 1 && state->tree) {
+                        n = rb_next(&state->rb_node);
+                        while (n) {
+                                state = rb_entry(n, struct extent_state,
+                                                 rb_node);
+                                if (state->state & bits)
+                                        goto got_it;
+                                n = rb_next(n);
+                        }
+                        free_extent_state(*cached_state);
+                        *cached_state = NULL;
+                        goto out;
+                }
+                free_extent_state(*cached_state);
+                *cached_state = NULL;
+        }
+
         state = find_first_extent_bit_state(tree, start, bits);
+got_it:
         if (state) {
+                cache_state(state, cached_state);
                 *start_ret = state->start;
                 *end_ret = state->end;
                 ret = 0;
         }
+out:
         spin_unlock(&tree->lock);
         return ret;
 }