Btrfs: add initial tracepoint support for btrfs

Tracepoints can provide insight into why btrfs hits bugs and be greatly
helpful for debugging, e.g
              dd-7822  [000]  2121.641088: btrfs_inode_request: root = 5(FS_TREE), gen = 4, ino = 256, blocks = 8, disk_i_size = 0, last_trans = 8, logged_trans = 0
              dd-7822  [000]  2121.641100: btrfs_inode_new: root = 5(FS_TREE), gen = 8, ino = 257, blocks = 0, disk_i_size = 0, last_trans = 0, logged_trans = 0
 btrfs-transacti-7804  [001]  2146.935420: btrfs_cow_block: root = 2(EXTENT_TREE), refs = 2, orig_buf = 29368320 (orig_level = 0), cow_buf = 29388800 (cow_level = 0)
 btrfs-transacti-7804  [001]  2146.935473: btrfs_cow_block: root = 1(ROOT_TREE), refs = 2, orig_buf = 29364224 (orig_level = 0), cow_buf = 29392896 (cow_level = 0)
 btrfs-transacti-7804  [001]  2146.972221: btrfs_transaction_commit: root = 1(ROOT_TREE), gen = 8
   flush-btrfs-2-7821  [001]  2155.824210: btrfs_chunk_alloc: root = 3(CHUNK_TREE), offset = 1103101952, size = 1073741824, num_stripes = 1, sub_stripes = 0, type = DATA
   flush-btrfs-2-7821  [001]  2155.824241: btrfs_cow_block: root = 2(EXTENT_TREE), refs = 2, orig_buf = 29388800 (orig_level = 0), cow_buf = 29396992 (cow_level = 0)
   flush-btrfs-2-7821  [001]  2155.824255: btrfs_cow_block: root = 4(DEV_TREE), refs = 2, orig_buf = 29372416 (orig_level = 0), cow_buf = 29401088 (cow_level = 0)
   flush-btrfs-2-7821  [000]  2155.824329: btrfs_cow_block: root = 3(CHUNK_TREE), refs = 2, orig_buf = 20971520 (orig_level = 0), cow_buf = 20975616 (cow_level = 0)
 btrfs-endio-wri-7800  [001]  2155.898019: btrfs_cow_block: root = 5(FS_TREE), refs = 2, orig_buf = 29384704 (orig_level = 0), cow_buf = 29405184 (cow_level = 0)
 btrfs-endio-wri-7800  [001]  2155.898043: btrfs_cow_block: root = 7(CSUM_TREE), refs = 2, orig_buf = 29376512 (orig_level = 0), cow_buf = 29409280 (cow_level = 0)

Here is what I have added:

1) ordere_extent:
        btrfs_ordered_extent_add
        btrfs_ordered_extent_remove
        btrfs_ordered_extent_start
        btrfs_ordered_extent_put

These provide critical information to understand how ordered_extents are
updated.

2) extent_map:
        btrfs_get_extent

extent_map is used in both read and write cases, and it is useful for tracking
how btrfs specific IO is running.

3) writepage:
        __extent_writepage
        btrfs_writepage_end_io_hook

Pages are cirtical resourses and produce a lot of corner cases during writeback,
so it is valuable to know how page is written to disk.

4) inode:
        btrfs_inode_new
        btrfs_inode_request
        btrfs_inode_evict

These can show where and when a inode is created, when a inode is evicted.

5) sync:
        btrfs_sync_file
        btrfs_sync_fs

These show sync arguments.

6) transaction:
        btrfs_transaction_commit

In transaction based filesystem, it will be useful to know the generation and
who does commit.

7) back reference and cow:
	btrfs_delayed_tree_ref
	btrfs_delayed_data_ref
	btrfs_delayed_ref_head
	btrfs_cow_block

Btrfs natively supports back references, these tracepoints are helpful on
understanding btrfs's COW mechanism.

8) chunk:
	btrfs_chunk_alloc
	btrfs_chunk_free

Chunk is a link between physical offset and logical offset, and stands for space
infomation in btrfs, and these are helpful on tracing space things.

9) reserved_extent:
	btrfs_reserved_extent_alloc
	btrfs_reserved_extent_free

These can show how btrfs uses its space.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 083a55477375..a1c940425307 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -202,6 +202,8 @@ static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
         INIT_LIST_HEAD(&entry->list);
         INIT_LIST_HEAD(&entry->root_extent_list);
 
+        trace_btrfs_ordered_extent_add(inode, entry);
+
         spin_lock(&tree->lock);
         node = tree_insert(&tree->tree, file_offset,
                            &entry->rb_node);
@@ -387,6 +389,8 @@ int btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
         struct list_head *cur;
         struct btrfs_ordered_sum *sum;
 
+        trace_btrfs_ordered_extent_put(entry->inode, entry);
+
         if (atomic_dec_and_test(&entry->refs)) {
                 while (!list_empty(&entry->list)) {
                         cur = entry->list.next;
@@ -420,6 +424,8 @@ static int __btrfs_remove_ordered_extent(struct inode *inode,
         spin_lock(&root->fs_info->ordered_extent_lock);
         list_del_init(&entry->root_extent_list);
 
+        trace_btrfs_ordered_extent_remove(inode, entry);
+
         /*
          * we have no more ordered extents for this inode and
          * no dirty pages.  We can safely remove it from the
@@ -585,6 +591,8 @@ void btrfs_start_ordered_extent(struct inode *inode,
         u64 start = entry->file_offset;
         u64 end = start + entry->len - 1;
 
+        trace_btrfs_ordered_extent_start(inode, entry);
+
         /*
          * pages in the range can be dirty, clean or writeback.  We
          * start IO on any dirty ones so the wait doesn't stall waiting