On Mon 13-05-24 15:21:19, Zhang Yi wrote: > From: Zhang Yi <yi.zhang@xxxxxxxxxx> > > jbd2_transaction_committed() is used to check whether a transaction with > the given tid has already committed, it hold j_state_lock in read mode > and check the tid of current running transaction and committing > transaction, but holding the j_state_lock is expensive. > > We have already stored the sequence number of the most recently > committed transaction in journal t->j_commit_sequence, we could do this > check by comparing it with the given tid instead. If the given tid isn't > smaller than j_commit_sequence, we can ensure that the given transaction > has been committed. That way we could drop the expensive lock and > achieve about 10% ~ 20% performance gains in concurrent DIOs on may > virtual machine with 100G ramdisk. > > fio -filename=/mnt/foo -direct=1 -iodepth=10 -rw=$rw -ioengine=libaio \ > -bs=4k -size=10G -numjobs=10 -runtime=60 -overwrite=1 -name=test \ > -group_reporting > > Before: > overwrite IOPS=88.2k, BW=344MiB/s > read IOPS=95.7k, BW=374MiB/s > rand overwrite IOPS=98.7k, BW=386MiB/s > randread IOPS=102k, BW=397MiB/s > > After: > verwrite: IOPS=105k, BW=410MiB/s > read: IOPS=112k, BW=436MiB/s > rand overwrite: IOPS=104k, BW=404MiB/s > randread: IOPS=111k, BW=432MiB/s > > CC: Dave Chinner <david@xxxxxxxxxxxxx> > Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx> > Link: https://lore.kernel.org/linux-ext4/493ab4c5-505c-a351-eefa-7d2677cdf800@xxxxxxxxxxxxxxx/T/#m6a14df5d085527a188c5a151191e87a3252dc4e2 > Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx> I agree this is workable solution and the performance benefits are nice. But I have some comments regarding the implementation: > @@ -3199,8 +3199,8 @@ static bool ext4_inode_datasync_dirty(struct inode *inode) > journal_t *journal = EXT4_SB(inode->i_sb)->s_journal; > > if (journal) { > - if (jbd2_transaction_committed(journal, > - EXT4_I(inode)->i_datasync_tid)) > + if (tid_geq(journal->j_commit_sequence, > + EXT4_I(inode)->i_datasync_tid)) Please leave the helper jbd2_transaction_committed(), just make the implementation more efficient. Also accessing j_commit_sequence without any lock is theoretically problematic wrt compiler optimization. You should have READ_ONCE() there and the places modifying j_commit_sequence need to use WRITE_ONCE(). Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
