Btrfs: Leaf reference cache update

This changes the reference cache to make a single cache per root
instead of one cache per transaction, and to key by the byte number
of the disk block instead of the keys inside.

This makes it much less likely to have cache misses if a snapshot
or something has an extra reference on a higher node or a leaf while
the first transaction that added the leaf into the cache is dropping.

Some throttling is added to functions that free blocks heavily so they
wait for old transactions to drop.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 6 insertions, 12 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7b24f15..0e294cf 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1004,8 +1004,6 @@ int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 			goto out;
 		}
 
-		btrfs_item_key_to_cpu(buf, &ref->key, 0);
-
 		ref->bytenr = buf->start;
 		ref->owner = btrfs_header_owner(buf);
 		ref->generation = btrfs_header_generation(buf);
@@ -2387,19 +2385,15 @@ static void noinline reada_walk_down(struct btrfs_root *root,
 	}
 }
 
-/*
- * we want to avoid as much random IO as we can with the alloc mutex
- * held, so drop the lock and do the lookup, then do it again with the
- * lock held.
- */
 int drop_snap_lookup_refcount(struct btrfs_root *root, u64 start, u64 len,
 			      u32 *refs)
 {
+	int ret;
 	mutex_unlock(&root->fs_info->alloc_mutex);
-	lookup_extent_ref(NULL, root, start, len, refs);
+	ret = lookup_extent_ref(NULL, root, start, len, refs);
 	cond_resched();
 	mutex_lock(&root->fs_info->alloc_mutex);
-	return lookup_extent_ref(NULL, root, start, len, refs);
+	return ret;
 }
 
 /*
@@ -2468,11 +2462,11 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
 			BUG_ON(ret);
 			continue;
 		}
-		
+
 		if (*level == 1) {
 			struct btrfs_key key;
 			btrfs_node_key_to_cpu(cur, &key, path->slots[*level]);
-			ref = btrfs_lookup_leaf_ref(root, &key);
+			ref = btrfs_lookup_leaf_ref(root, bytenr);
 			if (ref) {
 				ret = drop_leaf_ref(trans, root, ref);
 				BUG_ON(ret);
@@ -2482,7 +2476,6 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
 				break;
 			}
 		}
-
 		next = btrfs_find_tree_block(root, bytenr, blocksize);
 		if (!next || !btrfs_buffer_uptodate(next, ptr_gen)) {
 			free_extent_buffer(next);
@@ -2672,6 +2665,7 @@ int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
 			ret = -EAGAIN;
 			break;
 		}
+		wake_up(&root->fs_info->transaction_throttle);
 	}
 	for (i = 0; i <= orig_level; i++) {
 		if (path->nodes[i]) {