On Mon 27-05-24 16:48:24, Luis Henriques wrote: > On Mon 27 May 2024 09:29:40 AM +01, Luis Henriques wrote; > >>> + /* > >>> + * Used to flag an inode as part of the next fast commit; will be > >>> + * reset during fast commit clean-up > >>> + */ > >>> + tid_t i_fc_next; > >>> + > >> > >> Do we really need new tid in the inode? I'd be kind of hoping we could use > >> EXT4_I(inode)->i_sync_tid for this - I can see we even already set it in > >> ext4_fc_track_template() and used for similar comparisons in fast commit > >> code. > > > > Ah, true. It looks like it could be used indeed. We'll still need a flag > > here, but a simple bool should be enough for that. > > After looking again at the code, I'm not 100% sure that this is actually > doable. For example, if I replace the above by > > bool i_fc_next; > > and set to to 'true' below: > > >>> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c > >>> index 87c009e0c59a..bfdf249f0783 100644 > >>> --- a/fs/ext4/fast_commit.c > >>> +++ b/fs/ext4/fast_commit.c > >>> @@ -402,6 +402,8 @@ static int ext4_fc_track_template( > >>> sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING) ? > >>> &sbi->s_fc_q[FC_Q_STAGING] : > >>> &sbi->s_fc_q[FC_Q_MAIN]); > >>> + else > >>> + ei->i_fc_next = tid; > > ei->i_fc_next = true; > > Then, when we get to the ext4_fc_cleanup(), the value of iter->i_sync_tid > may have changed in the meantime from, e.g., ext4_do_update_inode() or > __ext4_iget(). This would cause the clean-up code to be bogus if it still > implements a the logic below, by comparing the tid with i_sync_tid. > (Although, to be honest, I couldn't see any visible effect in the quick > testing I've done.) Or am I missing something, and this is *exactly* the > behaviour you'd expect? Yes, this is the behavior I'd expect. The rationale is that if i_sync_tid points to the running transaction, it means the inode was modified in it, which means fastcommit needs to write it out. In fact the ext4_update_inode_fsync_trans() calls usually happen together with ext4_fc_track_...() calls. This could use some cleanup so that we don't set i_sync_tid in two places unnecessarily but that's for some other time... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
