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>

3 files changed, 17 insertions, 5 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 9997a59e4f58..99eb2bcd9aa7 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1492,6 +1492,7 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_MOUNT_AUTO_DEFRAG         (1 << 16)
 #define BTRFS_MOUNT_INODE_MAP_CACHE     (1 << 17)
 #define BTRFS_MOUNT_RECOVERY            (1 << 18)
+#define BTRFS_MOUNT_SKIP_BALANCE        (1 << 19)
 
 #define btrfs_clear_opt(o, opt)         ((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)           ((o) |= BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 34a8b6112ea4..063b521e3ded 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -164,8 +164,9 @@ enum {
         Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
         Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
         Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
-        Opt_enospc_debug, Opt_subvolrootid, Opt_defrag,
-        Opt_inode_cache, Opt_no_space_cache, Opt_recovery, Opt_err,
+        Opt_enospc_debug, Opt_subvolrootid, Opt_defrag, Opt_inode_cache,
+        Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
+        Opt_err,
 };
 
 static match_table_t tokens = {
@@ -200,6 +201,7 @@ static match_table_t tokens = {
         {Opt_inode_cache, "inode_cache"},
         {Opt_no_space_cache, "nospace_cache"},
         {Opt_recovery, "recovery"},
+        {Opt_skip_balance, "skip_balance"},
         {Opt_err, NULL},
 };
 
@@ -398,6 +400,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                         printk(KERN_INFO "btrfs: enabling auto recovery");
                         btrfs_set_opt(info->mount_opt, RECOVERY);
                         break;
+                case Opt_skip_balance:
+                        btrfs_set_opt(info->mount_opt, SKIP_BALANCE);
+                        break;
                 case Opt_err:
                         printk(KERN_INFO "btrfs: unrecognized mount option "
                                "'%s'\n", p);
@@ -723,6 +728,8 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
                 seq_puts(seq, ",autodefrag");
         if (btrfs_test_opt(root, INODE_MAP_CACHE))
                 seq_puts(seq, ",inode_cache");
+        if (btrfs_test_opt(root, SKIP_BALANCE))
+                seq_puts(seq, ",skip_balance");
         return 0;
 }
 
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);