Josef Bacik
2011-Apr-11 20:56 UTC
[PATCH] Btrfs: avoid taking the trans_mutex in btrfs_end_transaction V2
I''ve been working on making our O_DIRECT latency not suck and I noticed
we were
taking the trans_mutex in btrfs_end_transaction. So to do this we convert
num_writers and use_count to atomic_t''s and just decrement them in
btrfs_end_transaction. Instead of deleting the transaction from the trans list
in put_transaction we do that in btrfs_commit_transaction() since
that''s the
only time it actually needs to be removed from the list. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
---
V1->V2: make put_transaction just free the transaction and then change
btrfs_commit_transaction to do the trans list deletion.
fs/btrfs/disk-io.c | 2 +-
fs/btrfs/transaction.c | 37 ++++++++++++++++---------------------
fs/btrfs/transaction.h | 4 ++--
3 files changed, 19 insertions(+), 24 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 8f1d44b..68c84c8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3057,7 +3057,7 @@ static int btrfs_cleanup_transaction(struct btrfs_root
*root)
btrfs_destroy_pinned_extent(root,
root->fs_info->pinned_extents);
- t->use_count = 0;
+ atomic_set(&t->use_count, 0);
list_del_init(&t->list);
memset(t, 0, sizeof(*t));
kmem_cache_free(btrfs_transaction_cachep, t);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 4583008..c571734 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -32,10 +32,8 @@
static noinline void put_transaction(struct btrfs_transaction *transaction)
{
- WARN_ON(transaction->use_count == 0);
- transaction->use_count--;
- if (transaction->use_count == 0) {
- list_del_init(&transaction->list);
+ WARN_ON(atomic_read(&transaction->use_count) == 0);
+ if (atomic_dec_and_test(&transaction->use_count)) {
memset(transaction, 0, sizeof(*transaction));
kmem_cache_free(btrfs_transaction_cachep, transaction);
}
@@ -60,14 +58,14 @@ static noinline int join_transaction(struct btrfs_root
*root)
if (!cur_trans)
return -ENOMEM;
root->fs_info->generation++;
- cur_trans->num_writers = 1;
+ atomic_set(&cur_trans->num_writers, 1);
cur_trans->num_joined = 0;
cur_trans->transid = root->fs_info->generation;
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->use_count = 1;
+ atomic_set(&cur_trans->use_count, 1);
cur_trans->commit_done = 0;
cur_trans->start_time = get_seconds();
@@ -88,7 +86,7 @@ static noinline int join_transaction(struct btrfs_root *root)
root->fs_info->running_transaction = cur_trans;
spin_unlock(&root->fs_info->new_trans_lock);
} else {
- cur_trans->num_writers++;
+ atomic_inc(&cur_trans->num_writers);
cur_trans->num_joined++;
}
@@ -145,7 +143,7 @@ static void wait_current_trans(struct btrfs_root *root)
cur_trans = root->fs_info->running_transaction;
if (cur_trans && cur_trans->blocked) {
DEFINE_WAIT(wait);
- cur_trans->use_count++;
+ atomic_inc(&cur_trans->use_count);
while (1) {
prepare_to_wait(&root->fs_info->transaction_wait, &wait,
TASK_UNINTERRUPTIBLE);
@@ -205,7 +203,7 @@ again:
}
cur_trans = root->fs_info->running_transaction;
- cur_trans->use_count++;
+ atomic_inc(&cur_trans->use_count);
if (type != TRANS_JOIN_NOLOCK)
mutex_unlock(&root->fs_info->trans_mutex);
@@ -336,7 +334,7 @@ int btrfs_wait_for_commit(struct btrfs_root *root, u64
transid)
goto out_unlock; /* nothing committing|committed */
}
- cur_trans->use_count++;
+ atomic_inc(&cur_trans->use_count);
mutex_unlock(&root->fs_info->trans_mutex);
wait_for_commit(root, cur_trans);
@@ -466,18 +464,14 @@ static int __btrfs_end_transaction(struct
btrfs_trans_handle *trans,
wake_up_process(info->transaction_kthread);
}
- if (lock)
- mutex_lock(&info->trans_mutex);
WARN_ON(cur_trans != info->running_transaction);
- WARN_ON(cur_trans->num_writers < 1);
- cur_trans->num_writers--;
+ WARN_ON(atomic_read(&cur_trans->num_writers) < 1);
+ atomic_dec(&cur_trans->num_writers);
smp_mb();
if (waitqueue_active(&cur_trans->writer_wait))
wake_up(&cur_trans->writer_wait);
put_transaction(cur_trans);
- if (lock)
- mutex_unlock(&info->trans_mutex);
if (current->journal_info == trans)
current->journal_info = NULL;
@@ -1187,7 +1181,7 @@ int btrfs_commit_transaction_async(struct
btrfs_trans_handle *trans,
/* take transaction reference */
mutex_lock(&root->fs_info->trans_mutex);
cur_trans = trans->transaction;
- cur_trans->use_count++;
+ atomic_inc(&cur_trans->use_count);
mutex_unlock(&root->fs_info->trans_mutex);
btrfs_end_transaction(trans, root);
@@ -1246,7 +1240,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle
*trans,
mutex_lock(&root->fs_info->trans_mutex);
if (cur_trans->in_commit) {
- cur_trans->use_count++;
+ atomic_inc(&cur_trans->use_count);
mutex_unlock(&root->fs_info->trans_mutex);
btrfs_end_transaction(trans, root);
@@ -1268,7 +1262,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle
*trans,
prev_trans = list_entry(cur_trans->list.prev,
struct btrfs_transaction, list);
if (!prev_trans->commit_done) {
- prev_trans->use_count++;
+ atomic_inc(&prev_trans->use_count);
mutex_unlock(&root->fs_info->trans_mutex);
wait_for_commit(root, prev_trans);
@@ -1309,14 +1303,14 @@ int btrfs_commit_transaction(struct btrfs_trans_handle
*trans,
TASK_UNINTERRUPTIBLE);
smp_mb();
- if (cur_trans->num_writers > 1)
+ if (atomic_read(&cur_trans->num_writers) > 1)
schedule_timeout(MAX_SCHEDULE_TIMEOUT);
else if (should_grow)
schedule_timeout(1);
mutex_lock(&root->fs_info->trans_mutex);
finish_wait(&cur_trans->writer_wait, &wait);
- } while (cur_trans->num_writers > 1 ||
+ } while (atomic_read(&cur_trans->num_writers) > 1 ||
(should_grow && cur_trans->num_joined != joined));
ret = create_pending_snapshots(trans, root->fs_info);
@@ -1403,6 +1397,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle
*trans,
wake_up(&cur_trans->commit_wait);
+ list_del_init(&cur_trans->list);
put_transaction(cur_trans);
put_transaction(cur_trans);
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 229a594..e441acc 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -27,11 +27,11 @@ struct btrfs_transaction {
* total writers in this transaction, it must be zero before the
* transaction can end
*/
- unsigned long num_writers;
+ atomic_t num_writers;
unsigned long num_joined;
int in_commit;
- int use_count;
+ atomic_t use_count;
int commit_done;
int blocked;
struct list_head list;
--
1.7.2.3
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