On Wed 19-12-12 09:46:51, Eric Sandeen wrote: > On 12/19/12 2:13 AM, Jan Kara wrote: > > On Tue 18-12-12 21:08:51, Eric Sandeen wrote: > >> On 12/18/12 8:05 PM, Jan Kara wrote: > >>> On Wed 19-12-12 02:27:10, Jan Kara wrote: > >>>>> With a u8 tid_t, the "else" clause from commit d9b0193 fires > >>>>> frequently; I really think the underlying problem is that tid_geq() > >>>>> etc does not properly handle wraparounds - if, say, target is 255 > >>>>> and j_commit_request is 0, we don't know if j_commit_request > >>>>> is 255 tids behind, or 1 tid ahead. I have to think about that > >>>>> some more, unless it's obvious to someone else. > >>>> Well, there's no way to handle wraps better AFAICT. Tids eventually wrap > >>>> and if someone has stored away tid of a transaction he wants committed and > >>>> keeps it for a long time before using it, it can end up being anywhere > >>>> before / after current j_commit_request. The hope was that it takes long > >>>> enough to wrap around 32-bit tids. If this happens often in practice we may > >>>> have to switch to 64-bit tids (in memory, on disk 32-bit tids are enough > >>>> because of limited journal size). > >> > >> I was wondering if, since the tid_g*() functions only work if the > >> distance is half the unsigned int space, we can force a commit at some > >> point if j_transaction_sequence has gotten too far ahead? I'm not sure > >> where or if that could be done... > > I don't quiete understand. If someone stores tid = transaction->t_tid and > > in two weeks calls log_start_commit(tid), I don't see how any forcing of > > commits could solve that tid may now look ahead of the log... > > I'm probably missing something, but I was thinking we could compare > j_commit_sequence to j_transaction_sequence and force a commit up to at least > j_commit_sequence if it's too "stale" - but I'm only handwaving. :) You are probably missing the fact that j_transaction_sequence - 2 <= j_commit_sequence <= j_transaction_sequence. I.e., we have always one running transaction and at most one committing transaction which is the previous one. j_commit_sequence is TID of the transaction which successfully finished commit. The warnings we are seeing are caused by TIDs stored in EXT3_I(inode)->i_datasync_tid (and i_sync_tid). Those can get rather old before they are used. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
