On Thu, Mar 04, 2021 at 12:59:33PM +1100, Dave Chinner wrote: > On Wed, Mar 03, 2021 at 12:32:39PM -0500, Brian Foster wrote: > > On Wed, Mar 03, 2021 at 11:57:52AM +1100, Dave Chinner wrote: > > > On Tue, Mar 02, 2021 at 04:44:12PM -0500, Brian Foster wrote: > > > > On Thu, Feb 25, 2021 at 10:26:00AM +1100, Dave Chinner wrote: > > > > > * xlog_cil_push() handles racing pushes for the same sequence, > > > > > * so no need to deal with it here. > > > > > */ > > > > > restart: > > > > > - xlog_cil_push_now(log, sequence); > > > > > + xlog_cil_push_now(log, sequence, flags & XFS_LOG_SYNC); > > > > > + if (!(flags & XFS_LOG_SYNC)) > > > > > + return commit_lsn; > > > > > > > > Hm, so now we have sync and async log force and sync and async CIL push. > > > > A log force always requires a sync CIL push and commit record submit; > > > > the difference is simply whether or not we wait on commit record I/O > > > > completion. The sync CIL push drains the CIL of log items but does not > > > > switch out the commit record iclog, while the async CIL push executes in > > > > the workqueue context so the drain is async, but it does switch out the > > > > commit record iclog before it completes. IOW, the async CIL push is > > > > basically a "more async" async log force. > > > > > > Yes. > > > > > > > I can see the need for the behavior of the async CIL push here, but that > > > > leaves a mess of interfaces and behavior matrix. Is there any reason we > > > > couldn't just make async log forces unconditionally behave equivalent to > > > > the async CIL push as defined by this patch? There's only a handful of > > > > existing users and I don't see any obvious reason why they might care > > > > whether the underlying CIL push is synchronous or not... > > > > > > I'm not touching the rest of the log force code in this series - it > > > is out of scope of this bug fix and the rest of the series that it > > > is part of. > > > > > > > But you already have altered the log force code by changing > > xlog_cil_force_seq(), which implicitly changes how xfs_log_force_seq() > > behaves. > > The behaviour of the function when called from xfs_log_force*() > should be unchanged. Can you be specific about exactly what > behaviour did I change for non-synchronous xfs_log_force*() callers > so I can fix it? I have not intended to change it at all, so > whatever you are refering is an issue I need to fix... > xfs_log_force_seq() passes flags from the caller to xlog_cil_force_seq() (whereas this patch presumably wants it to pass XFS_LOG_SYNC unconditionally). IOW, xfs_log_force(mp, 0) behavior is different from xfs_log_force_seq(mp, seq, 0, ...). > > So not only does this patch expose subsystem internals to > > external layers and create more log forcing interfaces/behaviors to > > Sorry, I don't follow. What "subsystem internals" are being exposed > and what external layer are they being exposed to? > > > > Cleaning up the mess that is the xfs_log_* and xlog_* interfaces and > > > changing things like log force behaviour and implementation is for > > > a future series. > > > > > > > TBH I think this patch is kind of a mess on its own. I think the > > mechanism it wants to provide is sane, but I've not even got to the > > point of reviewing _that_ yet because of the seeming dismissal of higher > > level feedback. I'd rather not go around in circles on this so I'll just > > offer my summarized feedback to this patch... > > I'm not dismissing review nor am I saying the API cannot or should > not be improved. I'm simply telling you that I think the additional > changes you are proposing are outside the scope of the problem I am > addressing here. I already plan to rework the log force API (and > others) but doing so it not something that this patchset needs to > address, or indeed should address. > I'm not proposing additional changes nor to rework the log force API. I'm pointing out that I find this implementation to be extremely and unnecessarily confusing. To improve it, I'm suggesting to either coopt the existing async log force API... > There are already enough subtle changes being made to core code and > algorithms that mixing them with unrelated high level external > behavioural changes that it greatly increases the risk of unexpected > regressions in the patchset. The log force are paths are used in > data integrity paths, so I want to limit the scope of behavioural > change to just the AIL where the log force has no data integrity > requirement associcated with it. > ... or if we really want a special async log force just for xfsaild (why is still not clear to me), then tie it to an XFS_LOG_REALLY_ASYNC flag or some such, pass that to the existing log force call, and document the purpose/behavior of the new mode in detail. That at least won't require a developer to wonder what !(flags & XFS_LOG_SYNC) happens to mean depending on the particular log force function. Brian > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx >
