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Sun, 23 Jan 2022 17:23:39 +0000 (GMT) From: Ritesh Harjani To: linux-ext4@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jan Kara , tytso@mit.edu, Ritesh Harjani , Jan Kara Subject: [PATCHv1 1/2] jbd2: Kill t_handle_lock transaction spinlock Date: Sun, 23 Jan 2022 22:53:27 +0530 Message-Id: <089b38635884e95cfd858c003630bdc8bd7f22b0.1642953021.git.riteshh@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: References: X-TM-AS-GCONF: 00 X-Proofpoint-GUID: TAaMZ_L3fL3mTwTHHhdClEZ_F5t2OUVd X-Proofpoint-ORIG-GUID: TAaMZ_L3fL3mTwTHHhdClEZ_F5t2OUVd X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-23_05,2022-01-21_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 adultscore=0 phishscore=0 spamscore=0 bulkscore=0 mlxlogscore=711 malwarescore=0 mlxscore=0 lowpriorityscore=0 impostorscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201230132 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org This patch kills t_handle_lock transaction spinlock completely from jbd2. To explain the reasoning, currently there were three sites at which this spinlock was used. 1. jbd2_journal_wait_updates() a. Based on careful code review it can be seen that, we don't need this lock here. This is since we wait for any currently ongoing updates based on a atomic variable t_updates. And we anyway don't take any t_handle_lock while in stop_this_handle(). i.e. write_lock(&journal->j_state_lock() jbd2_journal_wait_updates() stop_this_handle() while (atomic_read(txn->t_updates) { | DEFINE_WAIT(wait); | prepare_to_wait(); | if (atomic_read(txn->t_updates) if (atomic_dec_and_test(txn->t_updates)) write_unlock(&journal->j_state_lock); schedule(); wake_up() write_lock(&journal->j_state_lock); finish_wait(); } txn->t_state = T_COMMIT write_unlock(&journal->j_state_lock); b. Also note that between atomic_inc(&txn->t_updates) in start_this_handle() and jbd2_journal_wait_updates(), the synchronization happens via read_lock(journal->j_state_lock) in start_this_handle(); 2. jbd2_journal_extend() a. jbd2_journal_extend() is called with the handle of each process from task_struct. So no lock required in updating member fields of handle_t b. For member fields of h_transaction, all updates happens only via atomic APIs (which is also within read_lock()). So, no need of this transaction spinlock. 3. update_t_max_wait() Based on Jan suggestion, this can be carefully removed using atomic cmpxchg API. Note that there can be several processes which are waiting for a new transaction to be allocated and started. For doing this only one process will succeed in taking write_lock() and allocating a new txn. After that all of the process will be updating the t_max_wait (max transaction wait time). This can be done via below method w/o taking any locks using atomic cmpxchg. For more details refer [1] new = get_new_val(); old = READ_ONCE(ptr->max_val); while (old < new) old = cmpxchg(&ptr->max_val, old, new); [1]: https://lwn.net/Articles/849237/ Suggested-by: Jan Kara Signed-off-by: Ritesh Harjani Reviewed-by: Jan Kara --- fs/jbd2/transaction.c | 29 +++++++++-------------------- include/linux/jbd2.h | 3 --- 2 files changed, 9 insertions(+), 23 deletions(-) -- 2.31.1 diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index 8e2f8275a253..68dd7de49aff 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -107,7 +107,6 @@ static void jbd2_get_transaction(journal_t *journal, transaction->t_start_time = ktime_get(); 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, jbd2_descriptor_blocks_per_trans(journal) + @@ -139,24 +138,21 @@ static void jbd2_get_transaction(journal_t *journal, /* * Update transaction's maximum wait time, if debugging is enabled. * - * In order for t_max_wait to be reliable, it must be protected by a - * lock. But doing so will mean that start_this_handle() can not be - * run in parallel on SMP systems, which limits our scalability. So - * unless debugging is enabled, we no longer update t_max_wait, which - * means that maximum wait time reported by the jbd2_run_stats - * tracepoint will always be zero. + * t_max_wait is carefully updated here with use of atomic compare exchange. + * Note that there could be multiplre threads trying to do this simultaneously + * hence using cmpxchg to avoid any use of locks in this case. */ static inline void update_t_max_wait(transaction_t *transaction, unsigned long ts) { #ifdef CONFIG_JBD2_DEBUG + unsigned long oldts, newts; if (jbd2_journal_enable_debug && time_after(transaction->t_start, ts)) { - ts = jbd2_time_diff(ts, transaction->t_start); - spin_lock(&transaction->t_handle_lock); - if (ts > transaction->t_max_wait) - transaction->t_max_wait = ts; - spin_unlock(&transaction->t_handle_lock); + newts = jbd2_time_diff(ts, transaction->t_start); + oldts = READ_ONCE(transaction->t_max_wait); + while (oldts < newts) + oldts = cmpxchg(&transaction->t_max_wait, oldts, newts); } #endif } @@ -690,7 +686,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks, int revoke_records) DIV_ROUND_UP( handle->h_revoke_credits_requested, journal->j_revoke_records_per_block); - spin_lock(&transaction->t_handle_lock); wanted = atomic_add_return(nblocks, &transaction->t_outstanding_credits); @@ -698,7 +693,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks, int revoke_records) jbd_debug(3, "denied handle %p %d blocks: " "transaction too large\n", handle, nblocks); atomic_sub(nblocks, &transaction->t_outstanding_credits); - goto unlock; + goto error_out; } trace_jbd2_handle_extend(journal->j_fs_dev->bd_dev, @@ -714,8 +709,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks, int revoke_records) result = 0; jbd_debug(3, "extended handle %p by %d\n", handle, nblocks); -unlock: - spin_unlock(&transaction->t_handle_lock); error_out: read_unlock(&journal->j_state_lock); return result; @@ -847,22 +840,18 @@ void jbd2_journal_wait_updates(journal_t *journal) if (!commit_transaction) return; - spin_lock(&commit_transaction->t_handle_lock); while (atomic_read(&commit_transaction->t_updates)) { DEFINE_WAIT(wait); prepare_to_wait(&journal->j_wait_updates, &wait, TASK_UNINTERRUPTIBLE); if (atomic_read(&commit_transaction->t_updates)) { - spin_unlock(&commit_transaction->t_handle_lock); write_unlock(&journal->j_state_lock); schedule(); write_lock(&journal->j_state_lock); - spin_lock(&commit_transaction->t_handle_lock); } finish_wait(&journal->j_wait_updates, &wait); } - spin_unlock(&commit_transaction->t_handle_lock); } /** diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h index 575c3057a98a..500a95f8c914 100644 --- a/include/linux/jbd2.h +++ b/include/linux/jbd2.h @@ -554,9 +554,6 @@ struct transaction_chp_stats_s { * ->j_list_lock * * j_state_lock - * ->t_handle_lock - * - * j_state_lock * ->j_list_lock (journal_unmap_buffer) * */ From patchwork Sun Jan 23 17:23:28 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ritesh Harjani X-Patchwork-Id: 1583157 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: bilbo.ozlabs.org; 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Sun, 23 Jan 2022 17:23:50 +0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 20NHNmAN37945738 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 23 Jan 2022 17:23:48 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0EB484C046; Sun, 23 Jan 2022 17:23:48 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 19E554C040; Sun, 23 Jan 2022 17:23:46 +0000 (GMT) Received: from localhost (unknown [9.43.59.179]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Sun, 23 Jan 2022 17:23:45 +0000 (GMT) From: Ritesh Harjani To: linux-ext4@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Jan Kara , tytso@mit.edu, Ritesh Harjani Subject: [PATCHv1 2/2] jbd2: Remove CONFIG_JBD2_DEBUG to update t_max_wait Date: Sun, 23 Jan 2022 22:53:28 +0530 Message-Id: X-Mailer: git-send-email 2.31.1 In-Reply-To: References: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: DHCJZvCUwtFXrW94og8llrKT-W8fpKpT X-Proofpoint-ORIG-GUID: DHCJZvCUwtFXrW94og8llrKT-W8fpKpT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2022-01-23_05,2022-01-21_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 bulkscore=0 malwarescore=0 phishscore=0 suspectscore=0 adultscore=0 impostorscore=0 mlxlogscore=738 lowpriorityscore=0 spamscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2201230132 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org CONFIG_JBD2_DEBUG and jbd2_journal_enable_debug knobs were added in update_t_max_wait(), since earlier it used to take a spinlock for updating t_max_wait, which could cause a bottleneck while starting a txn (start_this_handle()). Since in previous patch, we have killed t_handle_lock completely, we could get rid of this debug config and knob to let t_max_wait be updated by default again. Signed-off-by: Ritesh Harjani Reviewed-by: Jan Kara --- fs/jbd2/transaction.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) -- 2.31.1 diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index 68dd7de49aff..77634e2e118e 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -141,20 +141,19 @@ static void jbd2_get_transaction(journal_t *journal, * t_max_wait is carefully updated here with use of atomic compare exchange. * Note that there could be multiplre threads trying to do this simultaneously * hence using cmpxchg to avoid any use of locks in this case. + * With this t_max_wait can be updated w/o enabling jbd2_journal_enable_debug. */ static inline void update_t_max_wait(transaction_t *transaction, unsigned long ts) { -#ifdef CONFIG_JBD2_DEBUG unsigned long oldts, newts; - if (jbd2_journal_enable_debug && - time_after(transaction->t_start, ts)) { + + if (time_after(transaction->t_start, ts)) { newts = jbd2_time_diff(ts, transaction->t_start); oldts = READ_ONCE(transaction->t_max_wait); while (oldts < newts) oldts = cmpxchg(&transaction->t_max_wait, oldts, newts); } -#endif } /*