Merge tag 'perf-core-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core

Pull perf/core improvements and fixes from Arnaldo Carvalho de Melo:

 * Fix include order for bison/flex-generated C files, from Ben Hutchings

 * Build fixes and documentation corrections from David Ahern

 * Group parsing support, from Jiri Olsa

 * UI/gtk refactorings and improvements from Namhyung Kim

 * NULL deref fix for perf script, from Namhyung Kim

 * Assorted cleanups from Robert Richter

 * Let O= makes handle relative paths, from Steven Rostedt

 * perf script python fixes, from Feng Tang.

 * Improve 'perf lock' error message when the needed tracepoints
   are not present, from David Ahern.

 * Initial bash completion support, from Frederic Weisbecker

 * Allow building without libelf, from Namhyung Kim.

 * Support DWARF CFI based unwind to have callchains when %bp
   based unwinding is not possible, from Jiri Olsa.

 * Symbol resolution fixes, while fixing support PPC64 files with an .opt ELF
   section was the end goal, several fixes for code that handles all
   architectures and cleanups are included, from Cody Schafer.

 * Add a description for the JIT interface, from Andi Kleen.

 * Assorted fixes for Documentation and build in 32 bit, from Robert Richter

 * Add support for non-tracepoint events in perf script python, from Feng Tang

 * Cache the libtraceevent event_format associated to each evsel early, so that we
   avoid relookups, i.e. calling pevent_find_event repeatedly when processing
   tracepoint events.

   [ This is to reduce the surface contact with libtraceevents and make clear what
     is that the perf tools needs from that lib: so far parsing the common and per
     event fields. ]

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 240 insertions, 118 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 6e1d36702ff..4e1b153b7c4 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -34,6 +34,8 @@
 #include "locking.h"
 #include "free-space-cache.h"
 
+#undef SCRAMBLE_DELAYED_REFS
+
 /*
  * control flags for do_chunk_alloc's force field
  * CHUNK_ALLOC_NO_FORCE means to only allocate a chunk
@@ -2217,6 +2219,7 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 	struct btrfs_delayed_ref_node *ref;
 	struct btrfs_delayed_ref_head *locked_ref = NULL;
 	struct btrfs_delayed_extent_op *extent_op;
+	struct btrfs_fs_info *fs_info = root->fs_info;
 	int ret;
 	int count = 0;
 	int must_insert_reserved = 0;
@@ -2255,7 +2258,7 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 		ref = select_delayed_ref(locked_ref);
 
 		if (ref && ref->seq &&
-		    btrfs_check_delayed_seq(delayed_refs, ref->seq)) {
+		    btrfs_check_delayed_seq(fs_info, delayed_refs, ref->seq)) {
 			/*
 			 * there are still refs with lower seq numbers in the
 			 * process of being added. Don't run this ref yet.
@@ -2337,7 +2340,7 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
 		}
 
 next:
-		do_chunk_alloc(trans, root->fs_info->extent_root,
+		do_chunk_alloc(trans, fs_info->extent_root,
 			       2 * 1024 * 1024,
 			       btrfs_get_alloc_profile(root, 0),
 			       CHUNK_ALLOC_NO_FORCE);
@@ -2347,21 +2350,99 @@ next:
 	return count;
 }
 
-static void wait_for_more_refs(struct btrfs_delayed_ref_root *delayed_refs,
+static void wait_for_more_refs(struct btrfs_fs_info *fs_info,
+			       struct btrfs_delayed_ref_root *delayed_refs,
 			       unsigned long num_refs,
 			       struct list_head *first_seq)
 {
 	spin_unlock(&delayed_refs->lock);
 	pr_debug("waiting for more refs (num %ld, first %p)\n",
 		 num_refs, first_seq);
-	wait_event(delayed_refs->seq_wait,
+	wait_event(fs_info->tree_mod_seq_wait,
 		   num_refs != delayed_refs->num_entries ||
-		   delayed_refs->seq_head.next != first_seq);
+		   fs_info->tree_mod_seq_list.next != first_seq);
 	pr_debug("done waiting for more refs (num %ld, first %p)\n",
-		 delayed_refs->num_entries, delayed_refs->seq_head.next);
+		 delayed_refs->num_entries, fs_info->tree_mod_seq_list.next);
 	spin_lock(&delayed_refs->lock);
 }
 
+#ifdef SCRAMBLE_DELAYED_REFS
+/*
+ * Normally delayed refs get processed in ascending bytenr order. This
+ * correlates in most cases to the order added. To expose dependencies on this
+ * order, we start to process the tree in the middle instead of the beginning
+ */
+static u64 find_middle(struct rb_root *root)
+{
+	struct rb_node *n = root->rb_node;
+	struct btrfs_delayed_ref_node *entry;
+	int alt = 1;
+	u64 middle;
+	u64 first = 0, last = 0;
+
+	n = rb_first(root);
+	if (n) {
+		entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+		first = entry->bytenr;
+	}
+	n = rb_last(root);
+	if (n) {
+		entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+		last = entry->bytenr;
+	}
+	n = root->rb_node;
+
+	while (n) {
+		entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
+		WARN_ON(!entry->in_tree);
+
+		middle = entry->bytenr;
+
+		if (alt)
+			n = n->rb_left;
+		else
+			n = n->rb_right;
+
+		alt = 1 - alt;
+	}
+	return middle;
+}
+#endif
+
+int btrfs_delayed_refs_qgroup_accounting(struct btrfs_trans_handle *trans,
+					 struct btrfs_fs_info *fs_info)
+{
+	struct qgroup_update *qgroup_update;
+	int ret = 0;
+
+	if (list_empty(&trans->qgroup_ref_list) !=
+	    !trans->delayed_ref_elem.seq) {
+		/* list without seq or seq without list */
+		printk(KERN_ERR "btrfs: qgroup accounting update error, list is%s empty, seq is %llu\n",
+			list_empty(&trans->qgroup_ref_list) ? "" : " not",
+			trans->delayed_ref_elem.seq);
+		BUG();
+	}
+
+	if (!trans->delayed_ref_elem.seq)
+		return 0;
+
+	while (!list_empty(&trans->qgroup_ref_list)) {
+		qgroup_update = list_first_entry(&trans->qgroup_ref_list,
+						 struct qgroup_update, list);
+		list_del(&qgroup_update->list);
+		if (!ret)
+			ret = btrfs_qgroup_account_ref(
+					trans, fs_info, qgroup_update->node,
+					qgroup_update->extent_op);
+		kfree(qgroup_update);
+	}
+
+	btrfs_put_tree_mod_seq(fs_info, &trans->delayed_ref_elem);
+
+	return ret;
+}
+
 /*
  * this starts processing the delayed reference count updates and
  * extent insertions we have queued up so far.  count can be
@@ -2398,11 +2479,18 @@ int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 		       2 * 1024 * 1024, btrfs_get_alloc_profile(root, 0),
 		       CHUNK_ALLOC_NO_FORCE);
 
+	btrfs_delayed_refs_qgroup_accounting(trans, root->fs_info);
+
 	delayed_refs = &trans->transaction->delayed_refs;
 	INIT_LIST_HEAD(&cluster);
 again:
 	consider_waiting = 0;
 	spin_lock(&delayed_refs->lock);
+
+#ifdef SCRAMBLE_DELAYED_REFS
+	delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
+#endif
+
 	if (count == 0) {
 		count = delayed_refs->num_entries * 2;
 		run_most = 1;
@@ -2437,7 +2525,7 @@ again:
 				num_refs = delayed_refs->num_entries;
 				first_seq = root->fs_info->tree_mod_seq_list.next;
 			} else {
-				wait_for_more_refs(delayed_refs,
+				wait_for_more_refs(root->fs_info, delayed_refs,
 						   num_refs, first_seq);
 				/*
 				 * after waiting, things have changed. we
@@ -2502,6 +2590,7 @@ again:
 	}
 out:
 	spin_unlock(&delayed_refs->lock);
+	assert_qgroups_uptodate(trans);
 	return 0;
 }
 
@@ -2581,8 +2670,10 @@ static noinline int check_delayed_ref(struct btrfs_trans_handle *trans,
 
 	node = rb_prev(node);
 	if (node) {
+		int seq = ref->seq;
+
 		ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
-		if (ref->bytenr == bytenr)
+		if (ref->bytenr == bytenr && ref->seq == seq)
 			goto out_unlock;
 	}
 
@@ -2903,8 +2994,13 @@ again:
 	}
 
 	spin_lock(&block_group->lock);
-	if (block_group->cached != BTRFS_CACHE_FINISHED) {
-		/* We're not cached, don't bother trying to write stuff out */
+	if (block_group->cached != BTRFS_CACHE_FINISHED ||
+	    !btrfs_test_opt(root, SPACE_CACHE)) {
+		/*
+		 * don't bother trying to write stuff out _if_
+		 * a) we're not cached,
+		 * b) we're with nospace_cache mount option.
+		 */
 		dcs = BTRFS_DC_WRITTEN;
 		spin_unlock(&block_group->lock);
 		goto out_put;
@@ -3134,6 +3230,8 @@ static int update_space_info(struct btrfs_fs_info *info, u64 flags,
 	init_waitqueue_head(&found->wait);
 	*space_info = found;
 	list_add_rcu(&found->list, &info->space_info);
+	if (flags & BTRFS_BLOCK_GROUP_DATA)
+		info->data_sinfo = found;
 	return 0;
 }
 
@@ -3263,12 +3361,6 @@ u64 btrfs_get_alloc_profile(struct btrfs_root *root, int data)
 	return get_alloc_profile(root, flags);
 }
 
-void btrfs_set_inode_space_info(struct btrfs_root *root, struct inode *inode)
-{
-	BTRFS_I(inode)->space_info = __find_space_info(root->fs_info,
-						       BTRFS_BLOCK_GROUP_DATA);
-}
-
 /*
  * This will check the space that the inode allocates from to make sure we have
  * enough space for bytes.
@@ -3277,6 +3369,7 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 {
 	struct btrfs_space_info *data_sinfo;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct btrfs_fs_info *fs_info = root->fs_info;
 	u64 used;
 	int ret = 0, committed = 0, alloc_chunk = 1;
 
@@ -3289,7 +3382,7 @@ int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
 		committed = 1;
 	}
 
-	data_sinfo = BTRFS_I(inode)->space_info;
+	data_sinfo = fs_info->data_sinfo;
 	if (!data_sinfo)
 		goto alloc;
 
@@ -3330,10 +3423,9 @@ alloc:
 					goto commit_trans;
 			}
 
-			if (!data_sinfo) {
-				btrfs_set_inode_space_info(root, inode);
-				data_sinfo = BTRFS_I(inode)->space_info;
-			}
+			if (!data_sinfo)
+				data_sinfo = fs_info->data_sinfo;
+
 			goto again;
 		}
 
@@ -3380,7 +3472,7 @@ void btrfs_free_reserved_data_space(struct inode *inode, u64 bytes)
 	/* make sure bytes are sectorsize aligned */
 	bytes = (bytes + root->sectorsize - 1) & ~((u64)root->sectorsize - 1);
 
-	data_sinfo = BTRFS_I(inode)->space_info;
+	data_sinfo = root->fs_info->data_sinfo;
 	spin_lock(&data_sinfo->lock);
 	data_sinfo->bytes_may_use -= bytes;
 	trace_btrfs_space_reservation(root->fs_info, "space_info",
@@ -3586,89 +3678,58 @@ out:
 /*
  * shrink metadata reservation for delalloc
  */
-static int shrink_delalloc(struct btrfs_root *root, u64 to_reclaim,
-			   bool wait_ordered)
+static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
+			    bool wait_ordered)
 {
 	struct btrfs_block_rsv *block_rsv;
 	struct btrfs_space_info *space_info;
 	struct btrfs_trans_handle *trans;
-	u64 reserved;
+	u64 delalloc_bytes;
 	u64 max_reclaim;
-	u64 reclaimed = 0;
 	long time_left;
 	unsigned long nr_pages = (2 * 1024 * 1024) >> PAGE_CACHE_SHIFT;
 	int loops = 0;
-	unsigned long progress;
 
 	trans = (struct btrfs_trans_handle *)current->journal_info;
 	block_rsv = &root->fs_info->delalloc_block_rsv;
 	space_info = block_rsv->space_info;
 
 	smp_mb();
-	reserved = space_info->bytes_may_use;
-	progress = space_info->reservation_progress;
-
-	if (reserved == 0)
-		return 0;
-
-	smp_mb();
-	if (root->fs_info->delalloc_bytes == 0) {
+	delalloc_bytes = root->fs_info->delalloc_bytes;
+	if (delalloc_bytes == 0) {
 		if (trans)
-			return 0;
+			return;
 		btrfs_wait_ordered_extents(root, 0, 0);
-		return 0;
+		return;
 	}
 
-	max_reclaim = min(reserved, to_reclaim);
-	nr_pages = max_t(unsigned long, nr_pages,
-			 max_reclaim >> PAGE_CACHE_SHIFT);
-	while (loops < 1024) {
-		/* have the flusher threads jump in and do some IO */
-		smp_mb();
-		nr_pages = min_t(unsigned long, nr_pages,
-		       root->fs_info->delalloc_bytes >> PAGE_CACHE_SHIFT);
+	while (delalloc_bytes && loops < 3) {
+		max_reclaim = min(delalloc_bytes, to_reclaim);
+		nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
 		writeback_inodes_sb_nr_if_idle(root->fs_info->sb, nr_pages,
-						WB_REASON_FS_FREE_SPACE);
+					       WB_REASON_FS_FREE_SPACE);
 
 		spin_lock(&space_info->lock);
-		if (reserved > space_info->bytes_may_use)
-			reclaimed += reserved - space_info->bytes_may_use;
-		reserved = space_info->bytes_may_use;
+		if (space_info->bytes_used + space_info->bytes_reserved +
+		    space_info->bytes_pinned + space_info->bytes_readonly +
+		    space_info->bytes_may_use + orig <=
+		    space_info->total_bytes) {
+			spin_unlock(&space_info->lock);
+			break;
+		}
 		spin_unlock(&space_info->lock);
 
 		loops++;
-
-		if (reserved == 0 || reclaimed >= max_reclaim)
-			break;
-
-		if (trans && trans->transaction->blocked)
-			return -EAGAIN;
-
 		if (wait_ordered && !trans) {
 			btrfs_wait_ordered_extents(root, 0, 0);
 		} else {
-			time_left = schedule_timeout_interruptible(1);
-
-			/* We were interrupted, exit */
+			time_left = schedule_timeout_killable(1);
 			if (time_left)
 				break;
 		}
-
-		/* we've kicked the IO a few times, if anything has been freed,
-		 * exit.  There is no sense in looping here for a long time
-		 * when we really need to commit the transaction, or there are
-		 * just too many writers without enough free space
-		 */
-
-		if (loops > 3) {
-			smp_mb();
-			if (progress != space_info->reservation_progress)
-				break;
-		}
-
+		smp_mb();
+		delalloc_bytes = root->fs_info->delalloc_bytes;
 	}
-
-	return reclaimed >= to_reclaim;
 }
 
 /**
@@ -3728,6 +3789,58 @@ commit:
 	return btrfs_commit_transaction(trans, root);
 }
 
+enum flush_state {
+	FLUSH_DELALLOC		=	1,
+	FLUSH_DELALLOC_WAIT	=	2,
+	FLUSH_DELAYED_ITEMS_NR	=	3,
+	FLUSH_DELAYED_ITEMS	=	4,
+	COMMIT_TRANS		=	5,
+};
+
+static int flush_space(struct btrfs_root *root,
+		       struct btrfs_space_info *space_info, u64 num_bytes,
+		       u64 orig_bytes, int state)
+{
+	struct btrfs_trans_handle *trans;
+	int nr;
+	int ret = 0;
+
+	switch (state) {
+	case FLUSH_DELALLOC:
+	case FLUSH_DELALLOC_WAIT:
+		shrink_delalloc(root, num_bytes, orig_bytes,
+				state == FLUSH_DELALLOC_WAIT);
+		break;
+	case FLUSH_DELAYED_ITEMS_NR:
+	case FLUSH_DELAYED_ITEMS:
+		if (state == FLUSH_DELAYED_ITEMS_NR) {
+			u64 bytes = btrfs_calc_trans_metadata_size(root, 1);
+
+			nr = (int)div64_u64(num_bytes, bytes);
+			if (!nr)
+				nr = 1;
+			nr *= 2;
+		} else {
+			nr = -1;
+		}
+		trans = btrfs_join_transaction(root);
+		if (IS_ERR(trans)) {
+			ret = PTR_ERR(trans);
+			break;
+		}
+		ret = btrfs_run_delayed_items_nr(trans, root, nr);
+		btrfs_end_transaction(trans, root);
+		break;
+	case COMMIT_TRANS:
+		ret = may_commit_transaction(root, space_info, orig_bytes, 0);
+		break;
+	default:
+		ret = -ENOSPC;
+		break;
+	}
+
+	return ret;
+}
 /**
  * reserve_metadata_bytes - try to reserve bytes from the block_rsv's space
  * @root - the root we're allocating for
@@ -3749,11 +3862,10 @@ static int reserve_metadata_bytes(struct btrfs_root *root,
 	struct btrfs_space_info *space_info = block_rsv->space_info;
 	u64 used;
 	u64 num_bytes = orig_bytes;
-	int retries = 0;
+	int flush_state = FLUSH_DELALLOC;
 	int ret = 0;
-	bool committed = false;
 	bool flushing = false;
-	bool wait_ordered = false;
+	bool committed = false;
 
 again:
 	ret = 0;
@@ -3812,9 +3924,8 @@ again:
 		 * amount plus the amount of bytes that we need for this
 		 * reservation.
 		 */
-		wait_ordered = true;
 		num_bytes = used - space_info->total_bytes +
-			(orig_bytes * (retries + 1));
+			(orig_bytes * 2);
 	}
 
 	if (ret) {
@@ -3867,8 +3978,6 @@ again:
 			trace_btrfs_space_reservation(root->fs_info,
 				"space_info", space_info->flags, orig_bytes, 1);
 			ret = 0;
-		} else {
-			wait_ordered = true;
 		}
 	}
 
@@ -3887,36 +3996,13 @@ again:
 	if (!ret || !flush)
 		goto out;
 
-	/*
-	 * We do synchronous shrinking since we don't actually unreserve
-	 * metadata until after the IO is completed.
-	 */
-	ret = shrink_delalloc(root, num_bytes, wait_ordered);
-	if (ret < 0)
-		goto out;
-
-	ret = 0;
-
-	/*
-	 * So if we were overcommitted it's possible that somebody else flushed
-	 * out enough space and we simply didn't have enough space to reclaim,
-	 * so go back around and try again.
-	 */
-	if (retries < 2) {
-		wait_ordered = true;
-		retries++;
+	ret = flush_space(root, space_info, num_bytes, orig_bytes,
+			  flush_state);
+	flush_state++;
+	if (!ret)
 		goto again;
-	}
-
-	ret = -ENOSPC;
-	if (committed)
-		goto out;
-
-	ret = may_commit_transaction(root, space_info, orig_bytes, 0);
-	if (!ret) {
-		committed = true;
+	else if (flush_state <= COMMIT_TRANS)
 		goto again;
-	}
 
 out:
 	if (flushing) {
@@ -3934,7 +4020,10 @@ static struct btrfs_block_rsv *get_block_rsv(
 {
 	struct btrfs_block_rsv *block_rsv = NULL;
 
-	if (root->ref_cows || root == root->fs_info->csum_root)
+	if (root->ref_cows)
+		block_rsv = trans->block_rsv;
+
+	if (root == root->fs_info->csum_root && trans->adding_csums)
 		block_rsv = trans->block_rsv;
 
 	if (!block_rsv)
@@ -4286,6 +4375,9 @@ static void release_global_block_rsv(struct btrfs_fs_info *fs_info)
 void btrfs_trans_release_metadata(struct btrfs_trans_handle *trans,
 				  struct btrfs_root *root)
 {
+	if (!trans->block_rsv)
+		return;
+
 	if (!trans->bytes_reserved)
 		return;
 
@@ -4444,7 +4536,7 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
 	int ret;
 
 	/* Need to be holding the i_mutex here if we aren't free space cache */
-	if (btrfs_is_free_space_inode(root, inode))
+	if (btrfs_is_free_space_inode(inode))
 		flush = 0;
 
 	if (flush && btrfs_transaction_in_commit(root->fs_info))
@@ -4476,6 +4568,13 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
 	csum_bytes = BTRFS_I(inode)->csum_bytes;
 	spin_unlock(&BTRFS_I(inode)->lock);
 
+	if (root->fs_info->quota_enabled) {
+		ret = btrfs_qgroup_reserve(root, num_bytes +
+					   nr_extents * root->leafsize);
+		if (ret)
+			return ret;
+	}
+
 	ret = reserve_metadata_bytes(root, block_rsv, to_reserve, flush);
 	if (ret) {
 		u64 to_free = 0;
@@ -4554,6 +4653,11 @@ void btrfs_delalloc_release_metadata(struct inode *inode, u64 num_bytes)
 
 	trace_btrfs_space_reservation(root->fs_info, "delalloc",
 				      btrfs_ino(inode), to_free, 0);
+	if (root->fs_info->quota_enabled) {
+		btrfs_qgroup_free(root, num_bytes +
+					dropped * root->leafsize);
+	}
+
 	btrfs_block_rsv_release(root, &root->fs_info->delalloc_block_rsv,
 				to_free);
 }
@@ -5190,8 +5294,9 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
 	rb_erase(&head->node.rb_node, &delayed_refs->root);
 
 	delayed_refs->num_entries--;
-	if (waitqueue_active(&delayed_refs->seq_wait))
-		wake_up(&delayed_refs->seq_wait);
+	smp_mb();
+	if (waitqueue_active(&root->fs_info->tree_mod_seq_wait))
+		wake_up(&root->fs_info->tree_mod_seq_wait);
 
 	/*
 	 * we don't take a ref on the node because we're removing it from the
@@ -5748,7 +5853,11 @@ loop:
 				ret = do_chunk_alloc(trans, root, num_bytes +
 						     2 * 1024 * 1024, data,
 						     CHUNK_ALLOC_LIMITED);
-				if (ret < 0) {
+				/*
+				 * Do not bail out on ENOSPC since we
+				 * can do more things.
+				 */
+				if (ret < 0 && ret != -ENOSPC) {
 					btrfs_abort_transaction(trans,
 								root, ret);
 					goto out;
@@ -5816,13 +5925,13 @@ static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
 again:
 	list_for_each_entry(cache, &info->block_groups[index], list) {
 		spin_lock(&cache->lock);
-		printk(KERN_INFO "block group %llu has %llu bytes, %llu used "
-		       "%llu pinned %llu reserved\n",
+		printk(KERN_INFO "block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %s\n",
 		       (unsigned long long)cache->key.objectid,
 		       (unsigned long long)cache->key.offset,
 		       (unsigned long long)btrfs_block_group_used(&cache->item),
 		       (unsigned long long)cache->pinned,
-		       (unsigned long long)cache->reserved);
+		       (unsigned long long)cache->reserved,
+		       cache->ro ? "[readonly]" : "");
 		btrfs_dump_free_space(cache, bytes);
 		spin_unlock(&cache->lock);
 	}
@@ -7610,8 +7719,21 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 		INIT_LIST_HEAD(&cache->list);
 		INIT_LIST_HEAD(&cache->cluster_list);
 
-		if (need_clear)
+		if (need_clear) {
+			/*
+			 * When we mount with old space cache, we need to
+			 * set BTRFS_DC_CLEAR and set dirty flag.
+			 *
+			 * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
+			 *    truncate the old free space cache inode and
+			 *    setup a new one.
+			 * b) Setting 'dirty flag' makes sure that we flush
+			 *    the new space cache info onto disk.
+			 */
 			cache->disk_cache_state = BTRFS_DC_CLEAR;
+			if (btrfs_test_opt(root, SPACE_CACHE))
+				cache->dirty = 1;
+		}
 
 		read_extent_buffer(leaf, &cache->item,
 				   btrfs_item_ptr_offset(leaf, path->slots[0]),