Btrfs: add skip_balance mount option

Since restriper kthread starts involuntarily on mount and can suck cpu
and memory bandwidth add a mount option to forcefully skip it.  The
restriper in that case hangs around in paused state and can be resumed
from userspace when it's convenient.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 17e565388de0..e0160607e6e2 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2707,15 +2707,19 @@ static int balance_kthread(void *data)
         struct btrfs_balance_control *bctl =
                         (struct btrfs_balance_control *)data;
         struct btrfs_fs_info *fs_info = bctl->fs_info;
-        int ret;
+        int ret = 0;
 
         mutex_lock(&fs_info->volume_mutex);
         mutex_lock(&fs_info->balance_mutex);
 
         set_balance_control(bctl);
 
-        printk(KERN_INFO "btrfs: continuing balance\n");
-        ret = btrfs_balance(bctl, NULL);
+        if (btrfs_test_opt(fs_info->tree_root, SKIP_BALANCE)) {
+                printk(KERN_INFO "btrfs: force skipping balance\n");
+        } else {
+                printk(KERN_INFO "btrfs: continuing balance\n");
+                ret = btrfs_balance(bctl, NULL);
+        }
 
         mutex_unlock(&fs_info->balance_mutex);
         mutex_unlock(&fs_info->volume_mutex);