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Message-Id: <1280851315-9167-2-git-send-email-tytso@mit.edu>
Date: Tue, 3 Aug 2010 12:01:53 -0400
From: Theodore Ts'o <tytso@....edu>
To: Ext4 Developers List <linux-ext4@...r.kernel.org>,
ocfs2-devel@....oracle.com
Cc: John Stultz <johnstul@...ibm.com>,
Keith Maanthey <kmannth@...ibm.com>,
Eric Whitney <eric.whitney@...com>,
Theodore Ts'o <tytso@....edu>
Subject: [PATCH, RFC 1/3] jbd2: Use atomic variables to avoid taking t_handle_lock in jbd2_journal_stop
By using an atomic_t for t_updates and t_outstanding credits, this
should allow us to not need to take transaction t_handle_lock in
jbd2_journal_stop().
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
fs/jbd2/checkpoint.c | 2 +-
fs/jbd2/commit.c | 13 +++++----
fs/jbd2/transaction.c | 69 +++++++++++++++++++++++++++---------------------
include/linux/jbd2.h | 8 +++---
4 files changed, 51 insertions(+), 41 deletions(-)
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 076d1cc..f8cdc02 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -775,7 +775,7 @@ void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transact
J_ASSERT(transaction->t_log_list == NULL);
J_ASSERT(transaction->t_checkpoint_list == NULL);
J_ASSERT(transaction->t_checkpoint_io_list == NULL);
- J_ASSERT(transaction->t_updates == 0);
+ J_ASSERT(atomic_read(&transaction->t_updates) == 0);
J_ASSERT(journal->j_committing_transaction != transaction);
J_ASSERT(journal->j_running_transaction != transaction);
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index af05681..fbd2c56 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -417,12 +417,12 @@ void jbd2_journal_commit_transaction(journal_t *journal)
stats.run.rs_locked);
spin_lock(&commit_transaction->t_handle_lock);
- while (commit_transaction->t_updates) {
+ while (atomic_read(&commit_transaction->t_updates)) {
DEFINE_WAIT(wait);
prepare_to_wait(&journal->j_wait_updates, &wait,
TASK_UNINTERRUPTIBLE);
- if (commit_transaction->t_updates) {
+ if (atomic_read(&commit_transaction->t_updates)) {
spin_unlock(&commit_transaction->t_handle_lock);
spin_unlock(&journal->j_state_lock);
schedule();
@@ -433,7 +433,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
}
spin_unlock(&commit_transaction->t_handle_lock);
- J_ASSERT (commit_transaction->t_outstanding_credits <=
+ J_ASSERT (atomic_read(&commit_transaction->t_outstanding_credits) <=
journal->j_max_transaction_buffers);
/*
@@ -527,11 +527,12 @@ void jbd2_journal_commit_transaction(journal_t *journal)
stats.run.rs_logging = jiffies;
stats.run.rs_flushing = jbd2_time_diff(stats.run.rs_flushing,
stats.run.rs_logging);
- stats.run.rs_blocks = commit_transaction->t_outstanding_credits;
+ stats.run.rs_blocks =
+ atomic_read(&commit_transaction->t_outstanding_credits);
stats.run.rs_blocks_logged = 0;
J_ASSERT(commit_transaction->t_nr_buffers <=
- commit_transaction->t_outstanding_credits);
+ atomic_read(&commit_transaction->t_outstanding_credits));
err = 0;
descriptor = NULL;
@@ -616,7 +617,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
* the free space in the log, but this counter is changed
* by jbd2_journal_next_log_block() also.
*/
- commit_transaction->t_outstanding_credits--;
+ atomic_dec(&commit_transaction->t_outstanding_credits);
/* Bump b_count to prevent truncate from stumbling over
the shadowed buffer! @@@ This can go if we ever get
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 001e95f..9c64c7e 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -55,6 +55,8 @@ jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
transaction->t_tid = journal->j_transaction_sequence++;
transaction->t_expires = jiffies + journal->j_commit_interval;
spin_lock_init(&transaction->t_handle_lock);
+ atomic_set(&transaction->t_updates, 0);
+ atomic_set(&transaction->t_outstanding_credits, 0);
INIT_LIST_HEAD(&transaction->t_inode_list);
INIT_LIST_HEAD(&transaction->t_private_list);
@@ -177,7 +179,7 @@ repeat_locked:
* checkpoint to free some more log space.
*/
spin_lock(&transaction->t_handle_lock);
- needed = transaction->t_outstanding_credits + nblocks;
+ needed = atomic_read(&transaction->t_outstanding_credits) + nblocks;
if (needed > journal->j_max_transaction_buffers) {
/*
@@ -240,11 +242,12 @@ repeat_locked:
}
handle->h_transaction = transaction;
- transaction->t_outstanding_credits += nblocks;
- transaction->t_updates++;
+ atomic_add(nblocks, &transaction->t_outstanding_credits);
+ atomic_inc(&transaction->t_updates);
transaction->t_handle_count++;
jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
- handle, nblocks, transaction->t_outstanding_credits,
+ handle, nblocks,
+ atomic_read(&transaction->t_outstanding_credits),
__jbd2_log_space_left(journal));
spin_unlock(&transaction->t_handle_lock);
spin_unlock(&journal->j_state_lock);
@@ -369,7 +372,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
}
spin_lock(&transaction->t_handle_lock);
- wanted = transaction->t_outstanding_credits + nblocks;
+ wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
if (wanted > journal->j_max_transaction_buffers) {
jbd_debug(3, "denied handle %p %d blocks: "
@@ -384,7 +387,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
}
handle->h_buffer_credits += nblocks;
- transaction->t_outstanding_credits += nblocks;
+ atomic_add(nblocks, &transaction->t_outstanding_credits);
result = 0;
jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
@@ -426,15 +429,14 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, int gfp_mask)
* First unlink the handle from its current transaction, and start the
* commit on that.
*/
- J_ASSERT(transaction->t_updates > 0);
+ J_ASSERT(atomic_read(&transaction->t_updates) > 0);
J_ASSERT(journal_current_handle() == handle);
spin_lock(&journal->j_state_lock);
spin_lock(&transaction->t_handle_lock);
- transaction->t_outstanding_credits -= handle->h_buffer_credits;
- transaction->t_updates--;
-
- if (!transaction->t_updates)
+ atomic_sub(handle->h_buffer_credits,
+ &transaction->t_outstanding_credits);
+ if (atomic_dec_and_test(&transaction->t_updates))
wake_up(&journal->j_wait_updates);
spin_unlock(&transaction->t_handle_lock);
@@ -481,7 +483,7 @@ void jbd2_journal_lock_updates(journal_t *journal)
break;
spin_lock(&transaction->t_handle_lock);
- if (!transaction->t_updates) {
+ if (!atomic_read(&transaction->t_updates)) {
spin_unlock(&transaction->t_handle_lock);
break;
}
@@ -1258,7 +1260,8 @@ int jbd2_journal_stop(handle_t *handle)
{
transaction_t *transaction = handle->h_transaction;
journal_t *journal = transaction->t_journal;
- int err;
+ int err, wait_for_commit = 0;
+ tid_t tid;
pid_t pid;
J_ASSERT(journal_current_handle() == handle);
@@ -1266,7 +1269,7 @@ int jbd2_journal_stop(handle_t *handle)
if (is_handle_aborted(handle))
err = -EIO;
else {
- J_ASSERT(transaction->t_updates > 0);
+ J_ASSERT(atomic_read(&transaction->t_updates) > 0);
err = 0;
}
@@ -1334,14 +1337,8 @@ int jbd2_journal_stop(handle_t *handle)
if (handle->h_sync)
transaction->t_synchronous_commit = 1;
current->journal_info = NULL;
- spin_lock(&transaction->t_handle_lock);
- transaction->t_outstanding_credits -= handle->h_buffer_credits;
- transaction->t_updates--;
- if (!transaction->t_updates) {
- wake_up(&journal->j_wait_updates);
- if (journal->j_barrier_count)
- wake_up(&journal->j_wait_transaction_locked);
- }
+ atomic_sub(handle->h_buffer_credits,
+ &transaction->t_outstanding_credits);
/*
* If the handle is marked SYNC, we need to set another commit
@@ -1350,15 +1347,13 @@ int jbd2_journal_stop(handle_t *handle)
* transaction is too old now.
*/
if (handle->h_sync ||
- transaction->t_outstanding_credits >
- journal->j_max_transaction_buffers ||
- time_after_eq(jiffies, transaction->t_expires)) {
+ (atomic_read(&transaction->t_outstanding_credits) >
+ journal->j_max_transaction_buffers) ||
+ time_after_eq(jiffies, transaction->t_expires)) {
/* Do this even for aborted journals: an abort still
* completes the commit thread, it just doesn't write
* anything to disk. */
- tid_t tid = transaction->t_tid;
- spin_unlock(&transaction->t_handle_lock);
jbd_debug(2, "transaction too old, requesting commit for "
"handle %p\n", handle);
/* This is non-blocking */
@@ -1369,11 +1364,25 @@ int jbd2_journal_stop(handle_t *handle)
* to wait for the commit to complete.
*/
if (handle->h_sync && !(current->flags & PF_MEMALLOC))
- err = jbd2_log_wait_commit(journal, tid);
- } else {
- spin_unlock(&transaction->t_handle_lock);
+ wait_for_commit = 1;
}
+ /*
+ * Once we drop t_updates, if it goes to zero the transaction
+ * could start commiting on us and eventually disappear. So
+ * once we do this, we must not dereference transaction
+ * pointer again.
+ */
+ tid = transaction->t_tid;
+ if (atomic_dec_and_test(&transaction->t_updates)) {
+ wake_up(&journal->j_wait_updates);
+ if (journal->j_barrier_count)
+ wake_up(&journal->j_wait_transaction_locked);
+ }
+
+ if (wait_for_commit)
+ err = jbd2_log_wait_commit(journal, tid);
+
lock_map_release(&handle->h_lockdep_map);
jbd2_free_handle(handle);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 5a72bc7..a72ce21 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -601,13 +601,13 @@ struct transaction_s
* Number of outstanding updates running on this transaction
* [t_handle_lock]
*/
- int t_updates;
+ atomic_t t_updates;
/*
* Number of buffers reserved for use by all handles in this transaction
* handle but not yet modified. [t_handle_lock]
*/
- int t_outstanding_credits;
+ atomic_t t_outstanding_credits;
/*
* Forward and backward links for the circular list of all transactions
@@ -1258,8 +1258,8 @@ static inline int jbd_space_needed(journal_t *journal)
{
int nblocks = journal->j_max_transaction_buffers;
if (journal->j_committing_transaction)
- nblocks += journal->j_committing_transaction->
- t_outstanding_credits;
+ nblocks += atomic_read(&journal->j_committing_transaction->
+ t_outstanding_credits);
return nblocks;
}
--
1.7.0.4
--
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