Btrfs: account for space used by the super mirrors

As we get closer to proper -ENOSPC handling in btrfs, we need more accurate
space accounting for the space info's.  Currently we exclude the free space for
the super mirrors, but the space they take up isn't accounted for in any of the
counters.  This patch introduces bytes_super, which keeps track of the amount
of bytes used for a super mirror in the block group cache and space info.  This
makes sure that our free space caclucations will be completely accurate.
Signed-off-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.h

@@ -674,6 +674,7 @@ struct btrfs_space_info {
 	u64 bytes_reserved;	/* total bytes the allocator has reserved for
 				   current allocations */
 	u64 bytes_readonly;	/* total bytes that are read only */
+	u64 bytes_super;	/* total bytes reserved for the super blocks */
 
 	/* delalloc accounting */
 	u64 bytes_delalloc;	/* number of bytes reserved for allocation,
@@ -746,6 +747,7 @@ struct btrfs_block_group_cache {
 	spinlock_t lock;
 	u64 pinned;
 	u64 reserved;
+	u64 bytes_super;
 	u64 flags;
 	u64 sectorsize;
 	int extents_thresh;

fs/btrfs/extent-tree.c

@@ -201,6 +201,7 @@ static int exclude_super_stripes(struct btrfs_root *root,
 		BUG_ON(ret);
 
 		while (nr--) {
+			cache->bytes_super += stripe_len;
 			ret = add_excluded_extent(root, logical[nr],
 						  stripe_len);
 			BUG_ON(ret);
@@ -295,6 +296,9 @@ static int caching_kthread(void *data)
 		return -ENOMEM;
 
 	exclude_super_stripes(extent_root, block_group);
+	spin_lock(&block_group->space_info->lock);
+	block_group->space_info->bytes_super += block_group->bytes_super;
+	spin_unlock(&block_group->space_info->lock);
 
 	last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);
 
@@ -2785,7 +2789,8 @@ again:
 	do_div(thresh, 100);
 
 	if (meta_sinfo->bytes_used + meta_sinfo->bytes_reserved +
-	    meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly > thresh) {
+	    meta_sinfo->bytes_pinned + meta_sinfo->bytes_readonly +
+	    meta_sinfo->bytes_super > thresh) {
 		struct btrfs_trans_handle *trans;
 		if (!meta_sinfo->full) {
 			meta_sinfo->force_alloc = 1;
@@ -2839,7 +2844,7 @@ again:
 	if (data_sinfo->total_bytes - data_sinfo->bytes_used -
 	    data_sinfo->bytes_delalloc - data_sinfo->bytes_reserved -
 	    data_sinfo->bytes_pinned - data_sinfo->bytes_readonly -
-	    data_sinfo->bytes_may_use < bytes) {
+	    data_sinfo->bytes_may_use - data_sinfo->bytes_super < bytes) {
 		struct btrfs_trans_handle *trans;
 
 		/*
@@ -6957,8 +6962,10 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 		 * time, particularly in the full case.
 		 */
 		if (found_key.offset == btrfs_block_group_used(&cache->item)) {
+			exclude_super_stripes(root, cache);
 			cache->last_byte_to_unpin = (u64)-1;
 			cache->cached = BTRFS_CACHE_FINISHED;
+			free_excluded_extents(root, cache);
 		} else if (btrfs_block_group_used(&cache->item) == 0) {
 			exclude_super_stripes(root, cache);
 			cache->last_byte_to_unpin = (u64)-1;
@@ -6975,6 +6982,10 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 					&space_info);
 		BUG_ON(ret);
 		cache->space_info = space_info;
+		spin_lock(&cache->space_info->lock);
+		cache->space_info->bytes_super += cache->bytes_super;
+		spin_unlock(&cache->space_info->lock);
+
 		down_write(&space_info->groups_sem);
 		list_add_tail(&cache->list, &space_info->block_groups);
 		up_write(&space_info->groups_sem);
@@ -7044,6 +7055,11 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans,
 	ret = update_space_info(root->fs_info, cache->flags, size, bytes_used,
 				&cache->space_info);
 	BUG_ON(ret);
+
+	spin_lock(&cache->space_info->lock);
+	cache->space_info->bytes_super += cache->bytes_super;
+	spin_unlock(&cache->space_info->lock);
+
 	down_write(&cache->space_info->groups_sem);
 	list_add_tail(&cache->list, &cache->space_info->block_groups);
 	up_write(&cache->space_info->groups_sem);