Re: [PATCH v7 4/9] ext4: rework fast commit commit path

Jan Kara
2024-12-13T15:12:05Z

On Sun 18-08-24 04:03:51, Harshad Shirwadkar wrote:
> This patch reworks fast commit's commit path to remove locking the
> journal for the entire duration of a fast commit. Instead, we only lock
> the journal while marking all the eligible inodes as "committing". This
> allows handles to make progress in parallel with the fast commit.
>
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/fast_commit.c | 74 ++++++++++++++++++++++++++++---------------
> fs/jbd2/journal.c | 2 --
> 2 files changed, 49 insertions(+), 27 deletions(-)
>
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index dfa999913..7a35234ce 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -291,20 +291,30 @@ void ext4_fc_del(struct inode *inode)
> if (ext4_fc_disabled(inode->i_sb))
> return;
>
> -restart:
> spin_lock(&EXT4_SB(inode->i_sb)->s_fc_lock);
> if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
> spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);
> return;
> }
>
> - if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
> - ext4_fc_wait_committing_inode(inode);
> - goto restart;
> - }
> -
> - if (!list_empty(&ei->i_fc_list))
> - list_del_init(&ei->i_fc_list);
> + /*
> + * Since ext4_fc_del is called from ext4_evict_inode while having a
> + * handle open, there is no need for us to wait here even if a fast
> + * commit is going on. That is because, if this inode is being
> + * committed, ext4_mark_inode_dirty would have waited for inode commit
> + * operation to finish before we come here. So, by the time we come
> + * here, inode's EXT4_STATE_FC_COMMITTING would have been cleared. So,
> + * we shouldn't see EXT4_STATE_FC_COMMITTING to be set on this inode
> + * here.
> + *
> + * We may come here without any handles open in the "no_delete" case of
> + * ext4_evict_inode as well. However, if that happens, we first mark the
> + * file system as fast commit ineligible anyway. So, even in that case,
> + * it is okay to remove the inode from the fc list.
> + */
> + WARN_ON(ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)
> + && !ext4_test_mount_flag(inode->i_sb, EXT4_MF_FC_INELIGIBLE));
> + list_del_init(&ei->i_fc_list);
>
> /*
> * Since this inode is getting removed, let's also remove all FC
> @@ -327,8 +337,6 @@ void ext4_fc_del(struct inode *inode)
> fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
> kfree(fc_dentry->fcd_name.name);
> kmem_cache_free(ext4_fc_dentry_cachep, fc_dentry);
> -
> - return;
> }
>
> /*
> @@ -1004,19 +1012,6 @@ static int ext4_fc_submit_inode_data_all(journal_t *journal)
>
> spin_lock(&sbi->s_fc_lock);
> list_for_each_entry(ei, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
> - ext4_set_inode_state(&ei->vfs_inode, EXT4_STATE_FC_COMMITTING);
> - while (atomic_read(&ei->i_fc_updates)) {
> - DEFINE_WAIT(wait);
> -
> - prepare_to_wait(&ei->i_fc_wait, &wait,
> - TASK_UNINTERRUPTIBLE);
> - if (atomic_read(&ei->i_fc_updates)) {
> - spin_unlock(&sbi->s_fc_lock);
> - schedule();
> - spin_lock(&sbi->s_fc_lock);
> - }
> - finish_wait(&ei->i_fc_wait, &wait);
> - }
> spin_unlock(&sbi->s_fc_lock);
> ret = jbd2_submit_inode_data(journal, ei->jinode);
> if (ret)
> @@ -1129,6 +1124,19 @@ static int ext4_fc_perform_commit(journal_t *journal)
> int ret = 0;
> u32 crc = 0;
>
> + /*
> + * Wait for all the handles of the current transaction to complete
> + * and then lock the journal.
> + */
> + jbd2_journal_lock_updates(journal);
> + spin_lock(&sbi->s_fc_lock);
> + list_for_each_entry(iter, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
> + ext4_set_inode_state(&iter->vfs_inode,
> + EXT4_STATE_FC_COMMITTING);
> + }
> + spin_unlock(&sbi->s_fc_lock);
> + jbd2_journal_unlock_updates(journal);
> +
> ret = ext4_fc_submit_inode_data_all(journal);
> if (ret)
> return ret;
> @@ -1179,6 +1187,18 @@ static int ext4_fc_perform_commit(journal_t *journal)
> ret = ext4_fc_write_inode(inode, &crc);
> if (ret)
> goto out;
> + ext4_clear_inode_state(inode, EXT4_STATE_FC_COMMITTING);
> + /*
> + * Make sure clearing of EXT4_STATE_FC_COMMITTING is
> + * visible before we send the wakeup. Pairs with implicit
> + * barrier in prepare_to_wait() in ext4_fc_track_inode().
> + */
> + smp_mb();
> +#if (BITS_PER_LONG < 64)
> + wake_up_bit(&iter->i_state_flags, EXT4_STATE_FC_COMMITTING);
> +#else
> + wake_up_bit(&iter->i_flags, EXT4_STATE_FC_COMMITTING);
> +#endif
> spin_lock(&sbi->s_fc_lock);
> }
> spin_unlock(&sbi->s_fc_lock);
> @@ -1316,13 +1336,17 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
> spin_lock(&sbi->s_fc_lock);
> list_for_each_entry_safe(iter, iter_n, &sbi->s_fc_q[FC_Q_MAIN],
> i_fc_list) {
> - list_del_init(&iter->i_fc_list);
> ext4_clear_inode_state(&iter->vfs_inode,
> EXT4_STATE_FC_COMMITTING);
> if (tid_geq(tid, iter->i_sync_tid))
> ext4_fc_reset_inode(&iter->vfs_inode);
> - /* Make sure EXT4_STATE_FC_COMMITTING bit is clear */
> + /*
> + * Make sure clearing of EXT4_STATE_FC_COMMITTING is
> + * visible before we send the wakeup. Pairs with implicit
> + * barrier in prepare_to_wait() in ext4_fc_track_inode().
> + */
> smp_mb();
> + list_del_init(&iter->i_fc_list);
> #if (BITS_PER_LONG < 64)
> wake_up_bit(&iter->i_state_flags, EXT4_STATE_FC_COMMITTING);
> #else
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 1ebf2393b..ecd70b506 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -728,7 +728,6 @@ int jbd2_fc_begin_commit(journal_t *journal, tid_t tid)
> }
> journal->j_flags |= JBD2_FAST_COMMIT_ONGOING;
> write_unlock(&journal->j_state_lock);
> - jbd2_journal_lock_updates(journal);
>
> return 0;
> }
> @@ -740,7 +739,6 @@ EXPORT_SYMBOL(jbd2_fc_begin_commit);
> */
> static int __jbd2_fc_end_commit(journal_t *journal, tid_t tid, bool fallback)
> {
> - jbd2_journal_unlock_updates(journal);
> if (journal->j_fc_cleanup_callback)
> journal->j_fc_cleanup_callback(journal, 0, tid);
> write_lock(&journal->j_state_lock);
> --
> 2.46.0.184.g6999bdac58-goog
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR