Btrfs: map the node block when looking for readahead targets
If we have particularly full nodes, we could call btrfs_node_blockptr up to 32
times, which is 32 pairs of kmap/kunmap, which _sucks_. So go ahead and map the
extent buffer while we look for readahead targets. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 84d7ca1..009bcf7 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1229,6 +1229,7 @@
u64 search;
u64 target;
u64 nread = 0;
+ u64 gen;
int direction = path->reada;
struct extent_buffer *eb;
u32 nr;
@@ -1256,6 +1257,15 @@
nritems = btrfs_header_nritems(node);
nr = slot;
while (1) {
+ if (!node->map_token) {
+ unsigned long offset = btrfs_node_key_ptr_offset(nr);
+ map_private_extent_buffer(node, offset,
+ sizeof(struct btrfs_key_ptr),
+ &node->map_token,
+ &node->kaddr,
+ &node->map_start,
+ &node->map_len, KM_USER1);
+ }
if (direction < 0) {
if (nr == 0)
break;
@@ -1273,14 +1283,23 @@
search = btrfs_node_blockptr(node, nr);
if ((search <= target && target - search <= 65536) ||
(search > target && search - target <= 65536)) {
- readahead_tree_block(root, search, blocksize,
- btrfs_node_ptr_generation(node, nr));
+ gen = btrfs_node_ptr_generation(node, nr);
+ if (node->map_token) {
+ unmap_extent_buffer(node, node->map_token,
+ KM_USER1);
+ node->map_token = NULL;
+ }
+ readahead_tree_block(root, search, blocksize, gen);
nread += blocksize;
}
nscan++;
if ((nread > 65536 || nscan > 32))
break;
}
+ if (node->map_token) {
+ unmap_extent_buffer(node, node->map_token, KM_USER1);
+ node->map_token = NULL;
+ }
}
/*