Btrfs: don't wait for the completion of all the ordered extents

It is very likely that there are lots of ordered extents in the filesytem,
if we wait for the completion of all of them when we want to reclaim some
space for the metadata space reservation, we would be blocked for a long
time. The performance would drop down suddenly for a long time.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 8a5eff366596..25a8f3812f14 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -565,10 +565,11 @@ static void btrfs_run_ordered_extent_work(struct btrfs_work *work)
  * wait for all the ordered extents in a root.  This is done when balancing
  * space between drives.
  */
-void btrfs_wait_ordered_extents(struct btrfs_root *root)
+int btrfs_wait_ordered_extents(struct btrfs_root *root, int nr)
 {
         struct list_head splice, works;
         struct btrfs_ordered_extent *ordered, *next;
+        int count = 0;
 
         INIT_LIST_HEAD(&splice);
         INIT_LIST_HEAD(&works);
@@ -576,7 +577,7 @@ void btrfs_wait_ordered_extents(struct btrfs_root *root)
         mutex_lock(&root->fs_info->ordered_operations_mutex);
         spin_lock(&root->ordered_extent_lock);
         list_splice_init(&root->ordered_extents, &splice);
-        while (!list_empty(&splice)) {
+        while (!list_empty(&splice) && nr) {
                 ordered = list_first_entry(&splice, struct btrfs_ordered_extent,
                                            root_extent_list);
                 list_move_tail(&ordered->root_extent_list,
@@ -591,7 +592,11 @@ void btrfs_wait_ordered_extents(struct btrfs_root *root)
 
                 cond_resched();
                 spin_lock(&root->ordered_extent_lock);
+                if (nr != -1)
+                        nr--;
+                count++;
         }
+        list_splice_tail(&splice, &root->ordered_extents);
         spin_unlock(&root->ordered_extent_lock);
 
         list_for_each_entry_safe(ordered, next, &works, work_list) {
@@ -601,18 +606,21 @@ void btrfs_wait_ordered_extents(struct btrfs_root *root)
                 cond_resched();
         }
         mutex_unlock(&root->fs_info->ordered_operations_mutex);
+
+        return count;
 }
 
-void btrfs_wait_all_ordered_extents(struct btrfs_fs_info *fs_info)
+void btrfs_wait_ordered_roots(struct btrfs_fs_info *fs_info, int nr)
 {
         struct btrfs_root *root;
         struct list_head splice;
+        int done;
 
         INIT_LIST_HEAD(&splice);
 
         spin_lock(&fs_info->ordered_root_lock);
         list_splice_init(&fs_info->ordered_roots, &splice);
-        while (!list_empty(&splice)) {
+        while (!list_empty(&splice) && nr) {
                 root = list_first_entry(&splice, struct btrfs_root,
                                         ordered_root);
                 root = btrfs_grab_fs_root(root);
@@ -621,10 +629,14 @@ void btrfs_wait_all_ordered_extents(struct btrfs_fs_info *fs_info)
                                &fs_info->ordered_roots);
                 spin_unlock(&fs_info->ordered_root_lock);
 
-                btrfs_wait_ordered_extents(root);
+                done = btrfs_wait_ordered_extents(root, nr);
                 btrfs_put_fs_root(root);
 
                 spin_lock(&fs_info->ordered_root_lock);
+                if (nr != -1) {
+                        nr -= done;
+                        WARN_ON(nr < 0);
+                }
         }
         spin_unlock(&fs_info->ordered_root_lock);
 }