Btrfs: Introduce contexts for metadata reservation

Introducing metadata reseravtion contexts has two major advantages.
First, it makes metadata reseravtion more traceable. Second, it can
reclaim freed space and re-add them to the itself after transaction
committed.

Besides add btrfs_block_rsv structure and related helper functions,
This patch contains following changes:

Move code that decides if freed tree block should be pinned into
btrfs_free_tree_block().

Make space accounting more accurate, mainly for handling read only
block groups.

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

1 files changed, 13 insertions, 3 deletions

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index e558dd941ded..d565b45a6352 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3514,6 +3514,7 @@ int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
         struct btrfs_fs_info *fs_info = extent_root->fs_info;
         struct reloc_control *rc;
         int ret;
+        int rw = 0;
         int err = 0;
 
         rc = kzalloc(sizeof(*rc), GFP_NOFS);
@@ -3524,15 +3525,22 @@ int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
         extent_io_tree_init(&rc->processed_blocks, NULL, GFP_NOFS);
         INIT_LIST_HEAD(&rc->reloc_roots);
 
+        rc->extent_root = extent_root;
         rc->block_group = btrfs_lookup_block_group(fs_info, group_start);
         BUG_ON(!rc->block_group);
 
+        if (!rc->block_group->ro) {
+                ret = btrfs_set_block_group_ro(extent_root, rc->block_group);
+                if (ret) {
+                        err = ret;
+                        goto out;
+                }
+                rw = 1;
+        }
+
         btrfs_init_workers(&rc->workers, "relocate",
                            fs_info->thread_pool_size, NULL);
 
-        rc->extent_root = extent_root;
-        btrfs_prepare_block_group_relocation(extent_root, rc->block_group);
-
         rc->data_inode = create_reloc_inode(fs_info, rc->block_group);
         if (IS_ERR(rc->data_inode)) {
                 err = PTR_ERR(rc->data_inode);
@@ -3597,6 +3605,8 @@ int btrfs_relocate_block_group(struct btrfs_root *extent_root, u64 group_start)
         WARN_ON(rc->block_group->reserved > 0);
         WARN_ON(btrfs_block_group_used(&rc->block_group->item) > 0);
 out:
+        if (err && rw)
+                btrfs_set_block_group_rw(extent_root, rc->block_group);
         iput(rc->data_inode);
         btrfs_stop_workers(&rc->workers);
         btrfs_put_block_group(rc->block_group);