Btrfs: leave btree locks spinning more often

btrfs_mark_buffer dirty would set dirty bits in the extent_io tree
for the buffers it was dirtying.  This may require a kmalloc and it
was not atomic.  So, anyone who called btrfs_mark_buffer_dirty had to
set any btree locks they were holding to blocking first.

This commit changes dirty tracking for extent buffers to just use a flag
in the extent buffer.  Now that we have one and only one extent buffer
per page, this can be safely done without losing dirty bits along the way.

This also introduces a path->leave_spinning flag that callers of
btrfs_search_slot can use to indicate they will properly deal with a
path returned where all the locks are spinning instead of blocking.

Many of the btree search callers now expect spinning paths,
resulting in better btree concurrency overall.

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

1 files changed, 11 insertions, 8 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 3764248bdc05..8686a3d2ab3a 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1684,7 +1684,8 @@ done:
          * we don't really know what they plan on doing with the path
          * from here on, so for now just mark it as blocking
          */
-        btrfs_set_path_blocking(p);
+        if (!p->leave_spinning)
+                btrfs_set_path_blocking(p);
         return ret;
 }
 
@@ -3032,26 +3033,27 @@ int btrfs_split_item(struct btrfs_trans_handle *trans,
                 return -EAGAIN;
         }
 
+        btrfs_set_path_blocking(path);
         ret = split_leaf(trans, root, &orig_key, path,
                          sizeof(struct btrfs_item), 1);
         path->keep_locks = 0;
         BUG_ON(ret);
 
+        btrfs_unlock_up_safe(path, 1);
+        leaf = path->nodes[0];
+        BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));
+
+split:
         /*
          * make sure any changes to the path from split_leaf leave it
          * in a blocking state
          */
         btrfs_set_path_blocking(path);
 
-        leaf = path->nodes[0];
-        BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));
-
-split:
         item = btrfs_item_nr(leaf, path->slots[0]);
         orig_offset = btrfs_item_offset(leaf, item);
         item_size = btrfs_item_size(leaf, item);
 
-
         buf = kmalloc(item_size, GFP_NOFS);
         read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
                             path->slots[0]), item_size);
@@ -3545,7 +3547,6 @@ setup_items_for_insert(struct btrfs_trans_handle *trans,
         }
 
         btrfs_set_header_nritems(leaf, nritems + nr);
-        btrfs_mark_buffer_dirty(leaf);
 
         ret = 0;
         if (slot == 0) {
@@ -3553,6 +3554,8 @@ setup_items_for_insert(struct btrfs_trans_handle *trans,
                 btrfs_cpu_key_to_disk(&disk_key, cpu_key);
                 ret = fixup_low_keys(trans, root, path, &disk_key, 1);
         }
+        btrfs_unlock_up_safe(path, 1);
+        btrfs_mark_buffer_dirty(leaf);
 
         if (btrfs_leaf_free_space(root, leaf) < 0) {
                 btrfs_print_leaf(root, leaf);
@@ -3596,7 +3599,6 @@ int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
                                total_data, total_size, nr);
 
 out:
-        btrfs_unlock_up_safe(path, 1);
         return ret;
 }
 
@@ -3792,6 +3794,7 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                         slot = path->slots[1];
                         extent_buffer_get(leaf);
 
+                        btrfs_set_path_blocking(path);
                         wret = push_leaf_left(trans, root, path, 1, 1);
                         if (wret < 0 && wret != -ENOSPC)
                                 ret = wret;