Btrfs: make the state of the transaction more readable
We used 3 variants to track the state of the transaction, it was complex
and wasted the memory space. Besides that, it was hard to understand that
which types of the transaction handles should be blocked in each transaction
state, so the developers often made mistakes.
This patch improved the above problem. In this patch, we define 6 states
for the transaction,
enum btrfs_trans_state {
TRANS_STATE_RUNNING = 0,
TRANS_STATE_BLOCKED = 1,
TRANS_STATE_COMMIT_START = 2,
TRANS_STATE_COMMIT_DOING = 3,
TRANS_STATE_UNBLOCKED = 4,
TRANS_STATE_COMPLETED = 5,
TRANS_STATE_MAX = 6,
}
and just use 1 variant to track those state.
In order to make the blocked handle types for each state more clear,
we introduce a array:
unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
[TRANS_STATE_RUNNING] = 0U,
[TRANS_STATE_BLOCKED] = (__TRANS_USERSPACE |
__TRANS_START),
[TRANS_STATE_COMMIT_START] = (__TRANS_USERSPACE |
__TRANS_START |
__TRANS_ATTACH),
[TRANS_STATE_COMMIT_DOING] = (__TRANS_USERSPACE |
__TRANS_START |
__TRANS_ATTACH |
__TRANS_JOIN),
[TRANS_STATE_UNBLOCKED] = (__TRANS_USERSPACE |
__TRANS_START |
__TRANS_ATTACH |
__TRANS_JOIN |
__TRANS_JOIN_NOLOCK),
[TRANS_STATE_COMPLETED] = (__TRANS_USERSPACE |
__TRANS_START |
__TRANS_ATTACH |
__TRANS_JOIN |
__TRANS_JOIN_NOLOCK),
}
it is very intuitionistic.
Besides that, because we remove ->in_commit in transaction structure, so
the lock ->commit_lock which was used to protect it is unnecessary, remove
->commit_lock.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 5e75ff4..eec8686 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -34,6 +34,29 @@
#define BTRFS_ROOT_TRANS_TAG 0
+static unsigned int btrfs_blocked_trans_types[TRANS_STATE_MAX] = {
+ [TRANS_STATE_RUNNING] = 0U,
+ [TRANS_STATE_BLOCKED] = (__TRANS_USERSPACE |
+ __TRANS_START),
+ [TRANS_STATE_COMMIT_START] = (__TRANS_USERSPACE |
+ __TRANS_START |
+ __TRANS_ATTACH),
+ [TRANS_STATE_COMMIT_DOING] = (__TRANS_USERSPACE |
+ __TRANS_START |
+ __TRANS_ATTACH |
+ __TRANS_JOIN),
+ [TRANS_STATE_UNBLOCKED] = (__TRANS_USERSPACE |
+ __TRANS_START |
+ __TRANS_ATTACH |
+ __TRANS_JOIN |
+ __TRANS_JOIN_NOLOCK),
+ [TRANS_STATE_COMPLETED] = (__TRANS_USERSPACE |
+ __TRANS_START |
+ __TRANS_ATTACH |
+ __TRANS_JOIN |
+ __TRANS_JOIN_NOLOCK),
+};
+
static void put_transaction(struct btrfs_transaction *transaction)
{
WARN_ON(atomic_read(&transaction->use_count) == 0);
@@ -50,13 +73,6 @@
root->commit_root = btrfs_root_node(root);
}
-static inline int can_join_transaction(struct btrfs_transaction *trans,
- unsigned int type)
-{
- return !(trans->in_commit &&
- (type & TRANS_EXTWRITERS));
-}
-
static inline void extwriter_counter_inc(struct btrfs_transaction *trans,
unsigned int type)
{
@@ -98,26 +114,13 @@
return -EROFS;
}
- if (fs_info->trans_no_join) {
- /*
- * If we are JOIN_NOLOCK we're already committing a current
- * transaction, we just need a handle to deal with something
- * when committing the transaction, such as inode cache and
- * space cache. It is a special case.
- */
- if (type != TRANS_JOIN_NOLOCK) {
- spin_unlock(&fs_info->trans_lock);
- return -EBUSY;
- }
- }
-
cur_trans = fs_info->running_transaction;
if (cur_trans) {
if (cur_trans->aborted) {
spin_unlock(&fs_info->trans_lock);
return cur_trans->aborted;
}
- if (!can_join_transaction(cur_trans, type)) {
+ if (btrfs_blocked_trans_types[cur_trans->state] & type) {
spin_unlock(&fs_info->trans_lock);
return -EBUSY;
}
@@ -136,6 +139,12 @@
if (type == TRANS_ATTACH)
return -ENOENT;
+ /*
+ * JOIN_NOLOCK only happens during the transaction commit, so
+ * it is impossible that ->running_transaction is NULL
+ */
+ BUG_ON(type == TRANS_JOIN_NOLOCK);
+
cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
if (!cur_trans)
return -ENOMEM;
@@ -144,7 +153,7 @@
if (fs_info->running_transaction) {
/*
* someone started a transaction after we unlocked. Make sure
- * to redo the trans_no_join checks above
+ * to redo the checks above
*/
kmem_cache_free(btrfs_transaction_cachep, cur_trans);
goto loop;
@@ -158,14 +167,12 @@
extwriter_counter_init(cur_trans, type);
init_waitqueue_head(&cur_trans->writer_wait);
init_waitqueue_head(&cur_trans->commit_wait);
- cur_trans->in_commit = 0;
- cur_trans->blocked = 0;
+ cur_trans->state = TRANS_STATE_RUNNING;
/*
* One for this trans handle, one so it will live on until we
* commit the transaction.
*/
atomic_set(&cur_trans->use_count, 2);
- cur_trans->commit_done = 0;
cur_trans->start_time = get_seconds();
cur_trans->delayed_refs.root = RB_ROOT;
@@ -188,7 +195,6 @@
"creating a fresh transaction\n");
atomic64_set(&fs_info->tree_mod_seq, 0);
- spin_lock_init(&cur_trans->commit_lock);
spin_lock_init(&cur_trans->delayed_refs.lock);
atomic_set(&cur_trans->delayed_refs.procs_running_refs, 0);
atomic_set(&cur_trans->delayed_refs.ref_seq, 0);
@@ -293,6 +299,12 @@
return 0;
}
+static inline int is_transaction_blocked(struct btrfs_transaction *trans)
+{
+ return (trans->state >= TRANS_STATE_BLOCKED &&
+ trans->state < TRANS_STATE_UNBLOCKED);
+}
+
/* wait for commit against the current transaction to become unblocked
* when this is done, it is safe to start a new transaction, but the current
* transaction might not be fully on disk.
@@ -303,12 +315,12 @@
spin_lock(&root->fs_info->trans_lock);
cur_trans = root->fs_info->running_transaction;
- if (cur_trans && cur_trans->blocked) {
+ if (cur_trans && is_transaction_blocked(cur_trans)) {
atomic_inc(&cur_trans->use_count);
spin_unlock(&root->fs_info->trans_lock);
wait_event(root->fs_info->transaction_wait,
- !cur_trans->blocked);
+ cur_trans->state >= TRANS_STATE_UNBLOCKED);
put_transaction(cur_trans);
} else {
spin_unlock(&root->fs_info->trans_lock);
@@ -432,7 +444,8 @@
INIT_LIST_HEAD(&h->new_bgs);
smp_mb();
- if (cur_trans->blocked && may_wait_transaction(root, type)) {
+ if (cur_trans->state >= TRANS_STATE_BLOCKED &&
+ may_wait_transaction(root, type)) {
btrfs_commit_transaction(h, root);
goto again;
}
@@ -536,7 +549,7 @@
static noinline void wait_for_commit(struct btrfs_root *root,
struct btrfs_transaction *commit)
{
- wait_event(commit->commit_wait, commit->commit_done);
+ wait_event(commit->commit_wait, commit->state == TRANS_STATE_COMPLETED);
}
int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid)
@@ -572,8 +585,8 @@
spin_lock(&root->fs_info->trans_lock);
list_for_each_entry_reverse(t, &root->fs_info->trans_list,
list) {
- if (t->in_commit) {
- if (t->commit_done)
+ if (t->state >= TRANS_STATE_COMMIT_START) {
+ if (t->state == TRANS_STATE_COMPLETED)
break;
cur_trans = t;
atomic_inc(&cur_trans->use_count);
@@ -614,7 +627,8 @@
int err;
smp_mb();
- if (cur_trans->blocked || cur_trans->delayed_refs.flushing)
+ if (cur_trans->state >= TRANS_STATE_BLOCKED ||
+ cur_trans->delayed_refs.flushing)
return 1;
updates = trans->delayed_ref_updates;
@@ -682,12 +696,15 @@
btrfs_create_pending_block_groups(trans, root);
if (lock && !atomic_read(&root->fs_info->open_ioctl_trans) &&
- should_end_transaction(trans, root)) {
- trans->transaction->blocked = 1;
- smp_wmb();
+ should_end_transaction(trans, root) &&
+ ACCESS_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
+ spin_lock(&info->trans_lock);
+ if (cur_trans->state == TRANS_STATE_RUNNING)
+ cur_trans->state = TRANS_STATE_BLOCKED;
+ spin_unlock(&info->trans_lock);
}
- if (lock && cur_trans->blocked && !cur_trans->in_commit) {
+ if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
if (throttle) {
/*
* We may race with somebody else here so end up having
@@ -1343,20 +1360,26 @@
int btrfs_transaction_in_commit(struct btrfs_fs_info *info)
{
+ struct btrfs_transaction *trans;
int ret = 0;
+
spin_lock(&info->trans_lock);
- if (info->running_transaction)
- ret = info->running_transaction->in_commit;
+ trans = info->running_transaction;
+ if (trans)
+ ret = (trans->state >= TRANS_STATE_COMMIT_START);
spin_unlock(&info->trans_lock);
return ret;
}
int btrfs_transaction_blocked(struct btrfs_fs_info *info)
{
+ struct btrfs_transaction *trans;
int ret = 0;
+
spin_lock(&info->trans_lock);
- if (info->running_transaction)
- ret = info->running_transaction->blocked;
+ trans = info->running_transaction;
+ if (trans)
+ ret = is_transaction_blocked(trans);
spin_unlock(&info->trans_lock);
return ret;
}
@@ -1368,7 +1391,8 @@
static void wait_current_trans_commit_start(struct btrfs_root *root,
struct btrfs_transaction *trans)
{
- wait_event(root->fs_info->transaction_blocked_wait, trans->in_commit);
+ wait_event(root->fs_info->transaction_blocked_wait,
+ trans->state >= TRANS_STATE_COMMIT_START);
}
/*
@@ -1379,7 +1403,7 @@
struct btrfs_transaction *trans)
{
wait_event(root->fs_info->transaction_wait,
- trans->commit_done || (trans->in_commit && !trans->blocked));
+ trans->state >= TRANS_STATE_UNBLOCKED);
}
/*
@@ -1484,18 +1508,22 @@
list_del_init(&cur_trans->list);
if (cur_trans == root->fs_info->running_transaction) {
- root->fs_info->trans_no_join = 1;
+ cur_trans->state = TRANS_STATE_COMMIT_DOING;
spin_unlock(&root->fs_info->trans_lock);
wait_event(cur_trans->writer_wait,
atomic_read(&cur_trans->num_writers) == 1);
spin_lock(&root->fs_info->trans_lock);
- root->fs_info->running_transaction = NULL;
}
spin_unlock(&root->fs_info->trans_lock);
btrfs_cleanup_one_transaction(trans->transaction, root);
+ spin_lock(&root->fs_info->trans_lock);
+ if (cur_trans == root->fs_info->running_transaction)
+ root->fs_info->running_transaction = NULL;
+ spin_unlock(&root->fs_info->trans_lock);
+
put_transaction(cur_trans);
put_transaction(cur_trans);
@@ -1507,10 +1535,6 @@
current->journal_info = NULL;
kmem_cache_free(btrfs_trans_handle_cachep, trans);
-
- spin_lock(&root->fs_info->trans_lock);
- root->fs_info->trans_no_join = 0;
- spin_unlock(&root->fs_info->trans_lock);
}
static int btrfs_flush_all_pending_stuffs(struct btrfs_trans_handle *trans,
@@ -1554,13 +1578,6 @@
btrfs_wait_all_ordered_extents(fs_info, 1);
}
-/*
- * btrfs_transaction state sequence:
- * in_commit = 0, blocked = 0 (initial)
- * in_commit = 1, blocked = 1
- * blocked = 0
- * commit_done = 1
- */
int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
struct btrfs_root *root)
{
@@ -1615,9 +1632,9 @@
return ret;
}
- spin_lock(&cur_trans->commit_lock);
- if (cur_trans->in_commit) {
- spin_unlock(&cur_trans->commit_lock);
+ spin_lock(&root->fs_info->trans_lock);
+ if (cur_trans->state >= TRANS_STATE_COMMIT_START) {
+ spin_unlock(&root->fs_info->trans_lock);
atomic_inc(&cur_trans->use_count);
ret = btrfs_end_transaction(trans, root);
@@ -1628,16 +1645,13 @@
return ret;
}
- trans->transaction->in_commit = 1;
- trans->transaction->blocked = 1;
- spin_unlock(&cur_trans->commit_lock);
+ cur_trans->state = TRANS_STATE_COMMIT_START;
wake_up(&root->fs_info->transaction_blocked_wait);
- spin_lock(&root->fs_info->trans_lock);
if (cur_trans->list.prev != &root->fs_info->trans_list) {
prev_trans = list_entry(cur_trans->list.prev,
struct btrfs_transaction, list);
- if (!prev_trans->commit_done) {
+ if (prev_trans->state != TRANS_STATE_COMPLETED) {
atomic_inc(&prev_trans->use_count);
spin_unlock(&root->fs_info->trans_lock);
@@ -1673,10 +1687,10 @@
/*
* Ok now we need to make sure to block out any other joins while we
* commit the transaction. We could have started a join before setting
- * no_join so make sure to wait for num_writers to == 1 again.
+ * COMMIT_DOING so make sure to wait for num_writers to == 1 again.
*/
spin_lock(&root->fs_info->trans_lock);
- root->fs_info->trans_no_join = 1;
+ cur_trans->state = TRANS_STATE_COMMIT_DOING;
spin_unlock(&root->fs_info->trans_lock);
wait_event(cur_trans->writer_wait,
atomic_read(&cur_trans->num_writers) == 1);
@@ -1803,10 +1817,9 @@
memcpy(root->fs_info->super_for_commit, root->fs_info->super_copy,
sizeof(*root->fs_info->super_copy));
- trans->transaction->blocked = 0;
spin_lock(&root->fs_info->trans_lock);
+ cur_trans->state = TRANS_STATE_UNBLOCKED;
root->fs_info->running_transaction = NULL;
- root->fs_info->trans_no_join = 0;
spin_unlock(&root->fs_info->trans_lock);
mutex_unlock(&root->fs_info->reloc_mutex);
@@ -1834,10 +1847,12 @@
btrfs_finish_extent_commit(trans, root);
- cur_trans->commit_done = 1;
-
root->fs_info->last_trans_committed = cur_trans->transid;
-
+ /*
+ * We needn't acquire the lock here because there is no other task
+ * which can change it.
+ */
+ cur_trans->state = TRANS_STATE_COMPLETED;
wake_up(&cur_trans->commit_wait);
spin_lock(&root->fs_info->trans_lock);