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Date:   Tue, 1 Oct 2019 00:43:10 -0700
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2 04/12] jbd2: fast-commit commit path changes

Thanks, done in V3.


On Fri, Aug 9, 2019 at 1:22 PM Andreas Dilger <adilger@...ger.ca> wrote:
>
> On Aug 8, 2019, at 9:45 PM, Harshad Shirwadkar <harshadshirwadkar@...il.com> wrote:
> >
> > This patch adds core fast-commit commit path changes. This patch also
> > modifies existing JBD2 APIs to allow usage of fast commits. If fast
> > commits are enabled and journal->j_do_full_commit is not set, the
> > commit routine tries the file system specific fast commmit first. Only
> > if it fails, it falls back to the full commit. Commit start and wait
> > APIs now take an additional argument which indicates if fast commits
> > are allowed or not.
> >
> > In this patch we also add a new entry to journal->stats which counts
> > the number of fast commits performed.
> >
> > Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
>
> It would be better to rename the existing function something like
> jbd2_log_start_commit_full() and add wrappers jbd2_log_start_commit()
> and jbd2_log_start_commit_fast() to avoid to change all of the
> callsites to add the same parameter:
>
> int jbd2_log_start_commit_fast(journal_t *journal, tid_t tid)
> {
>         return jbd2_log_start_commit_full(journal, tid, false);
> }
> EXPORT_SYMBOL(jbd2_log_start_commit_fast);
>
> int jbd2_log_start_commit(journal_t *journal, tid_t tid)
> {
>         return jbd2_log_start_commit_full(journal, tid, true);
> }
> EXPORT_SYMBOL(jbd2_log_start_commit);
>
> That makes it much more clear for the few callsites that need the
> "fast" variant what is being done, unlike a "true" or "false"
> argument to a function that isn't very clear what meaning it has.
>
> Cheers, Andreas
>
> > ---
> >
> > Changelog:
> >
> > V2: JBD2 commit routine passes stats to the fast commit callbac. Also,
> >    added a new entry to journal->stats and its tracking.
> > ---
> > fs/ext4/super.c       |  2 +-
> > fs/jbd2/checkpoint.c  |  2 +-
> > fs/jbd2/commit.c      | 47 +++++++++++++++++++++++--
> > fs/jbd2/journal.c     | 81 +++++++++++++++++++++++++++++++++++--------
> > fs/jbd2/transaction.c |  6 ++--
> > fs/ocfs2/alloc.c      |  2 +-
> > fs/ocfs2/super.c      |  2 +-
> > include/linux/jbd2.h  |  9 +++--
> > 8 files changed, 124 insertions(+), 27 deletions(-)
> >
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 81c3ec165822..6bab59ae81f7 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -5148,7 +5148,7 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
> >                   !jbd2_trans_will_send_data_barrier(sbi->s_journal, target))
> >                       needs_barrier = true;
> >
> > -             if (jbd2_journal_start_commit(sbi->s_journal, &target)) {
> > +             if (jbd2_journal_start_commit(sbi->s_journal, &target, true)) {
> >                       if (wait)
> >                               ret = jbd2_log_wait_commit(sbi->s_journal,
> >                                                          target);
> > diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> > index a1909066bde6..6297978ae3bc 100644
> > --- a/fs/jbd2/checkpoint.c
> > +++ b/fs/jbd2/checkpoint.c
> > @@ -277,7 +277,7 @@ int jbd2_log_do_checkpoint(journal_t *journal)
> >
> >                       if (batch_count)
> >                               __flush_batch(journal, &batch_count);
> > -                     jbd2_log_start_commit(journal, tid);
> > +                     jbd2_log_start_commit(journal, tid, true);
> >                       /*
> >                        * jbd2_journal_commit_transaction() may want
> >                        * to take the checkpoint_mutex if JBD2_FLUSHED
> > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> > index 132fb92098c7..9281814606e7 100644
> > --- a/fs/jbd2/commit.c
> > +++ b/fs/jbd2/commit.c
> > @@ -351,8 +351,12 @@ static void jbd2_block_tag_csum_set(journal_t *j, journal_block_tag_t *tag,
> >  *
> >  * The primary function for committing a transaction to the log.  This
> >  * function is called by the journal thread to begin a complete commit.
> > + *
> > + * fc is input / output parameter. If fc is non-null and is set to true, this
> > + * function tries to perform fast commit. If the fast commit is successfully
> > + * performed, *fc is set to true.
> >  */
> > -void jbd2_journal_commit_transaction(journal_t *journal)
> > +void jbd2_journal_commit_transaction(journal_t *journal, bool *fc)
> > {
> >       struct transaction_stats_s stats;
> >       transaction_t *commit_transaction;
> > @@ -380,6 +384,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >       tid_t first_tid;
> >       int update_tail;
> >       int csum_size = 0;
> > +     bool full_commit;
> >       LIST_HEAD(io_bufs);
> >       LIST_HEAD(log_bufs);
> >
> > @@ -413,6 +418,40 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >       J_ASSERT(journal->j_running_transaction != NULL);
> >       J_ASSERT(journal->j_committing_transaction == NULL);
> >
> > +     read_lock(&journal->j_state_lock);
> > +     full_commit = journal->j_do_full_commit;
> > +     read_unlock(&journal->j_state_lock);
> > +
> > +     /* Let file-system try its own fast commit */
> > +     if (jbd2_has_feature_fast_commit(journal)) {
> > +             if (!full_commit && fc && *fc == true &&
> > +                 journal->j_fc_commit_callback &&
> > +                 !journal->j_fc_commit_callback(
> > +                     journal, journal->j_running_transaction->t_tid,
> > +                     journal->j_subtid, &stats.run)) {
> > +                     jbd_debug(3, "fast commit success.\n");
> > +                     if (journal->j_fc_cleanup_callback)
> > +                             journal->j_fc_cleanup_callback(journal);
> > +                     write_lock(&journal->j_state_lock);
> > +                     journal->j_subtid++;
> > +                     if (fc)
> > +                             *fc = true;
> > +                     write_unlock(&journal->j_state_lock);
> > +                     goto update_overall_stats;
> > +             }
> > +             if (journal->j_fc_cleanup_callback)
> > +                     journal->j_fc_cleanup_callback(journal);
> > +             write_lock(&journal->j_state_lock);
> > +             journal->j_fc_off = 0;
> > +             journal->j_subtid = 0;
> > +             journal->j_do_full_commit = false;
> > +             write_unlock(&journal->j_state_lock);
> > +     }
> > +
> > +     jbd_debug(3, "fast commit not performed, trying full.\n");
> > +     if (fc)
> > +             *fc = false;
> > +
> >       commit_transaction = journal->j_running_transaction;
> >
> >       trace_jbd2_start_commit(journal, commit_transaction);
> > @@ -1129,8 +1168,12 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> >       /*
> >        * Calculate overall stats
> >        */
> > +update_overall_stats:
> >       spin_lock(&journal->j_history_lock);
> > -     journal->j_stats.ts_tid++;
> > +     if (fc && *fc == true)
> > +             journal->j_stats.ts_num_fast_commits++;
> > +     else
> > +             journal->j_stats.ts_tid++;
> >       journal->j_stats.ts_requested += stats.ts_requested;
> >       journal->j_stats.run.rs_wait += stats.run.rs_wait;
> >       journal->j_stats.run.rs_request_delay += stats.run.rs_request_delay;
> > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> > index 59ad709154a3..ab05e47ed2d4 100644
> > --- a/fs/jbd2/journal.c
> > +++ b/fs/jbd2/journal.c
> > @@ -160,7 +160,13 @@ static void commit_timeout(struct timer_list *t)
> >  *
> >  * 1) COMMIT:  Every so often we need to commit the current state of the
> >  *    filesystem to disk.  The journal thread is responsible for writing
> > - *    all of the metadata buffers to disk.
> > + *    all of the metadata buffers to disk. If fast commits are allowed,
> > + *    journal thread passes the control to the file system and file system
> > + *    is then responsible for writing metadata buffers to disk (in whichever
> > + *    format it wants). If fast commit succeds, journal thread won't perform
> > + *    a normal commit. In case the fast commit fails, journal thread performs
> > + *    full commit as normal.
> > + *
> >  *
> >  * 2) CHECKPOINT: We cannot reuse a used section of the log file until all
> >  *    of the data in that part of the log has been rewritten elsewhere on
> > @@ -172,6 +178,7 @@ static int kjournald2(void *arg)
> > {
> >       journal_t *journal = arg;
> >       transaction_t *transaction;
> > +     bool fc_flag = true, fc_flag_save;
> >
> >       /*
> >        * Set up an interval timer which can be used to trigger a commit wakeup
> > @@ -209,9 +216,14 @@ static int kjournald2(void *arg)
> >               jbd_debug(1, "OK, requests differ\n");
> >               write_unlock(&journal->j_state_lock);
> >               del_timer_sync(&journal->j_commit_timer);
> > -             jbd2_journal_commit_transaction(journal);
> > +             fc_flag_save = fc_flag;
> > +             jbd2_journal_commit_transaction(journal, &fc_flag);
> >               write_lock(&journal->j_state_lock);
> > -             goto loop;
> > +             if (!fc_flag) {
> > +                     /* fast commit not performed */
> > +                     fc_flag = fc_flag_save;
> > +                     goto loop;
> > +             }
> >       }
> >
> >       wake_up(&journal->j_wait_done_commit);
> > @@ -235,16 +247,18 @@ static int kjournald2(void *arg)
> >
> >               prepare_to_wait(&journal->j_wait_commit, &wait,
> >                               TASK_INTERRUPTIBLE);
> > -             if (journal->j_commit_sequence != journal->j_commit_request)
> > +             if (!fc_flag &&
> > +                 journal->j_commit_sequence != journal->j_commit_request)
> >                       should_sleep = 0;
> >               transaction = journal->j_running_transaction;
> >               if (transaction && time_after_eq(jiffies,
> > -                                             transaction->t_expires))
> > +                                              transaction->t_expires))
> >                       should_sleep = 0;
> >               if (journal->j_flags & JBD2_UNMOUNT)
> >                       should_sleep = 0;
> >               if (should_sleep) {
> >                       write_unlock(&journal->j_state_lock);
> > +                     jbd_debug(1, "%s sleeps\n", __func__);
> >                       schedule();
> >                       write_lock(&journal->j_state_lock);
> >               }
> > @@ -259,7 +273,10 @@ static int kjournald2(void *arg)
> >       transaction = journal->j_running_transaction;
> >       if (transaction && time_after_eq(jiffies, transaction->t_expires)) {
> >               journal->j_commit_request = transaction->t_tid;
> > +             fc_flag = false;
> >               jbd_debug(1, "woke because of timeout\n");
> > +     } else {
> > +             fc_flag = true;
> >       }
> >       goto loop;
> >
> > @@ -517,11 +534,17 @@ int __jbd2_log_start_commit(journal_t *journal, tid_t target)
> >       return 0;
> > }
> >
> > -int jbd2_log_start_commit(journal_t *journal, tid_t tid)
> > +int jbd2_log_start_commit(journal_t *journal, tid_t tid, bool full_commit)
> > {
> >       int ret;
> >
> >       write_lock(&journal->j_state_lock);
> > +     /*
> > +      * If someone has already requested a full commit,
> > +      * we have to honor it.
> > +      */
> > +     if (!journal->j_do_full_commit)
> > +             journal->j_do_full_commit = full_commit;
> >       ret = __jbd2_log_start_commit(journal, tid);
> >       write_unlock(&journal->j_state_lock);
> >       return ret;
> > @@ -556,7 +579,7 @@ static int __jbd2_journal_force_commit(journal_t *journal)
> >       tid = transaction->t_tid;
> >       read_unlock(&journal->j_state_lock);
> >       if (need_to_start)
> > -             jbd2_log_start_commit(journal, tid);
> > +             jbd2_log_start_commit(journal, tid, true);
> >       ret = jbd2_log_wait_commit(journal, tid);
> >       if (!ret)
> >               ret = 1;
> > @@ -603,11 +626,14 @@ int jbd2_journal_force_commit(journal_t *journal)
> >  * if a transaction is going to be committed (or is currently already
> >  * committing), and fills its tid in at *ptid
> >  */
> > -int jbd2_journal_start_commit(journal_t *journal, tid_t *ptid)
> > +int jbd2_journal_start_commit(journal_t *journal, tid_t *ptid, bool full_commit)
> > {
> >       int ret = 0;
> >
> >       write_lock(&journal->j_state_lock);
> > +     if (!journal->j_do_full_commit)
> > +             journal->j_do_full_commit = full_commit;
> > +
> >       if (journal->j_running_transaction) {
> >               tid_t tid = journal->j_running_transaction->t_tid;
> >
> > @@ -675,7 +701,7 @@ EXPORT_SYMBOL(jbd2_trans_will_send_data_barrier);
> >  * Wait for a specified commit to complete.
> >  * The caller may not hold the journal lock.
> >  */
> > -int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
> > +int __jbd2_log_wait_commit(journal_t *journal, tid_t tid, tid_t subtid)
> > {
> >       int err = 0;
> >
> > @@ -702,12 +728,25 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
> >       }
> > #endif
> >       while (tid_gt(tid, journal->j_commit_sequence)) {
> > -             jbd_debug(1, "JBD2: want %u, j_commit_sequence=%u\n",
> > -                               tid, journal->j_commit_sequence);
> > +             if ((!journal->j_do_full_commit) &&
> > +                 !tid_geq(subtid, journal->j_subtid))
> > +                     break;
> > +             jbd_debug(1, "JBD2: want full commit %u %s %u, ",
> > +                       tid, journal->j_do_full_commit ?
> > +                       "and ignoring fast commit request for " :
> > +                       "or want fast commit",
> > +                       journal->j_subtid);
> > +             jbd_debug(1, "j_commit_sequence=%u, j_subtid=%u\n",
> > +                       journal->j_commit_sequence, journal->j_subtid);
> >               read_unlock(&journal->j_state_lock);
> >               wake_up(&journal->j_wait_commit);
> > -             wait_event(journal->j_wait_done_commit,
> > -                             !tid_gt(tid, journal->j_commit_sequence));
> > +             if (journal->j_do_full_commit)
> > +                     wait_event(journal->j_wait_done_commit,
> > +                                !tid_gt(tid, journal->j_commit_sequence));
> > +             else
> > +                     wait_event(journal->j_wait_done_commit,
> > +                                !tid_gt(tid, journal->j_commit_sequence) ||
> > +                                !tid_geq(subtid, journal->j_subtid));
> >               read_lock(&journal->j_state_lock);
> >       }
> >       read_unlock(&journal->j_state_lock);
> > @@ -717,6 +756,13 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
> >       return err;
> > }
> >
> > +int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
> > +{
> > +     journal->j_do_full_commit = true;
> > +     return __jbd2_log_wait_commit(journal, tid, 0);
> > +}
> > +
> > +
> > /* Return 1 when transaction with given tid has already committed. */
> > int jbd2_transaction_committed(journal_t *journal, tid_t tid)
> > {
> > @@ -751,7 +797,7 @@ int jbd2_complete_transaction(journal_t *journal, tid_t tid)
> >               if (journal->j_commit_request != tid) {
> >                       /* transaction not yet started, so request it */
> >                       read_unlock(&journal->j_state_lock);
> > -                     jbd2_log_start_commit(journal, tid);
> > +                     jbd2_log_start_commit(journal, tid, true);
> >                       goto wait_commit;
> >               }
> >       } else if (!(journal->j_committing_transaction &&
> > @@ -996,6 +1042,8 @@ static int jbd2_seq_info_show(struct seq_file *seq, void *v)
> >                  "each up to %u blocks\n",
> >                  s->stats->ts_tid, s->stats->ts_requested,
> >                  s->journal->j_max_transaction_buffers);
> > +     seq_printf(seq, "%lu fast commits performed\n",
> > +                s->stats->ts_num_fast_commits);
> >       if (s->stats->ts_tid == 0)
> >               return 0;
> >       seq_printf(seq, "average: \n  %ums waiting for transaction\n",
> > @@ -1020,6 +1068,9 @@ static int jbd2_seq_info_show(struct seq_file *seq, void *v)
> >           s->stats->run.rs_blocks / s->stats->ts_tid);
> >       seq_printf(seq, "  %lu logged blocks per transaction\n",
> >           s->stats->run.rs_blocks_logged / s->stats->ts_tid);
> > +     seq_printf(seq, "  %lu logged blocks per commit\n",
> > +         s->stats->run.rs_blocks_logged /
> > +         (s->stats->ts_tid + s->stats->ts_num_fast_commits));
> >       return 0;
> > }
> >
> > @@ -1741,7 +1792,7 @@ int jbd2_journal_destroy(journal_t *journal)
> >
> >       /* Force a final log commit */
> >       if (journal->j_running_transaction)
> > -             jbd2_journal_commit_transaction(journal);
> > +             jbd2_journal_commit_transaction(journal, NULL);
> >
> >       /* Force any old transactions to disk */
> >
> > diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> > index 990e7b5062e7..87f6627d78aa 100644
> > --- a/fs/jbd2/transaction.c
> > +++ b/fs/jbd2/transaction.c
> > @@ -154,7 +154,7 @@ static void wait_transaction_locked(journal_t *journal)
> >       need_to_start = !tid_geq(journal->j_commit_request, tid);
> >       read_unlock(&journal->j_state_lock);
> >       if (need_to_start)
> > -             jbd2_log_start_commit(journal, tid);
> > +             jbd2_log_start_commit(journal, tid, true);
> >       jbd2_might_wait_for_commit(journal);
> >       schedule();
> >       finish_wait(&journal->j_wait_transaction_locked, &wait);
> > @@ -708,7 +708,7 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)
> >       need_to_start = !tid_geq(journal->j_commit_request, tid);
> >       read_unlock(&journal->j_state_lock);
> >       if (need_to_start)
> > -             jbd2_log_start_commit(journal, tid);
> > +             jbd2_log_start_commit(journal, tid, true);
> >
> >       rwsem_release(&journal->j_trans_commit_map, 1, _THIS_IP_);
> >       handle->h_buffer_credits = nblocks;
> > @@ -1822,7 +1822,7 @@ int jbd2_journal_stop(handle_t *handle)
> >               jbd_debug(2, "transaction too old, requesting commit for "
> >                                       "handle %p\n", handle);
> >               /* This is non-blocking */
> > -             jbd2_log_start_commit(journal, transaction->t_tid);
> > +             jbd2_log_start_commit(journal, transaction->t_tid, true);
> >
> >               /*
> >                * Special case: JBD2_SYNC synchronous updates require us
> > diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> > index 0c335b51043d..df41c43573b7 100644
> > --- a/fs/ocfs2/alloc.c
> > +++ b/fs/ocfs2/alloc.c
> > @@ -6117,7 +6117,7 @@ int ocfs2_try_to_free_truncate_log(struct ocfs2_super *osb,
> >               goto out;
> >       }
> >
> > -     if (jbd2_journal_start_commit(osb->journal->j_journal, &target)) {
> > +     if (jbd2_journal_start_commit(osb->journal->j_journal, &target, true)) {
> >               jbd2_log_wait_commit(osb->journal->j_journal, target);
> >               ret = 1;
> >       }
> > diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> > index 8b2f39506648..60ecc51759ae 100644
> > --- a/fs/ocfs2/super.c
> > +++ b/fs/ocfs2/super.c
> > @@ -410,7 +410,7 @@ static int ocfs2_sync_fs(struct super_block *sb, int wait)
> >       }
> >
> >       if (jbd2_journal_start_commit(osb->journal->j_journal,
> > -                                   &target)) {
> > +                                   &target, true)) {
> >               if (wait)
> >                       jbd2_log_wait_commit(osb->journal->j_journal,
> >                                            target);
> > diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> > index 153840b422cc..535f88dff653 100644
> > --- a/include/linux/jbd2.h
> > +++ b/include/linux/jbd2.h
> > @@ -742,6 +742,7 @@ struct transaction_run_stats_s {
> >
> > struct transaction_stats_s {
> >       unsigned long           ts_tid;
> > +     unsigned long           ts_num_fast_commits;
> >       unsigned long           ts_requested;
> >       struct transaction_run_stats_s run;
> > };
> > @@ -1364,7 +1365,8 @@ int __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);
> > void jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block);
> >
> > /* Commit management */
> > -extern void jbd2_journal_commit_transaction(journal_t *);
> > +extern void jbd2_journal_commit_transaction(journal_t *journal,
> > +                                         bool *full_commit);
> >
> > /* Checkpoint list management */
> > void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy);
> > @@ -1571,9 +1573,10 @@ extern void    jbd2_clear_buffer_revoked_flags(journal_t *journal);
> >  * transitions on demand.
> >  */
> >
> > -int jbd2_log_start_commit(journal_t *journal, tid_t tid);
> > +int jbd2_log_start_commit(journal_t *journal, tid_t tid, bool full_commit);
> > int __jbd2_log_start_commit(journal_t *journal, tid_t tid);
> > -int jbd2_journal_start_commit(journal_t *journal, tid_t *tid);
> > +int jbd2_journal_start_commit(journal_t *journal, tid_t *tid,
> > +                           bool full_commit);
> > int jbd2_log_wait_commit(journal_t *journal, tid_t tid);
> > int jbd2_transaction_committed(journal_t *journal, tid_t tid);
> > int jbd2_complete_transaction(journal_t *journal, tid_t tid);
> > --
> > 2.23.0.rc1.153.gdeed80330f-goog
> >
>
>
> Cheers, Andreas
>
>
>
>
>

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