> > > > Merged your improvement now (and I've split off the cleanup into a separate > > > > change and dropped the creation of fsnotify_path() which seemed a bit > > > > pointless with a single caller). All pushed out. > > > > > > > > > > > Jan & Jens, > > > > Although Jan has already queued this v3 patch with sufficient performance > > improvement for Jens' workloads, I got a performance regression report from > > kernel robot on will-it-scale microbenchmark (buffered write loop) > > on my fan_pre_content patches, so I tried to improve on the existing solution. > > > > I tried something similar to v1/v2 patches, where the sb keeps accounting > > of the number of watchers for specific sub-classes of events. > > > > I've made two major changes: > > 1. moved to counters into a per-sb state object fsnotify_sb_connector > > as Christian requested > > 2. The counters are by fanotify classes, not by specific events, so they > > can be used to answer the questions: > > a) Are there any fsnotify watchers on this sb? > > b) Are there any fanotify permission class listeners on this sb? > > c) Are there any fanotify pre-content (a.k.a HSM) class listeners on this sb? > > > > I think that those questions are very relevant in the real world, because > > a positive answer to (b) and (c) is quite rare in the real world, so the > > overhead on the permission hooks could be completely eliminated in > > the common case. > > > > If needed, we can further bisect the class counters per specific painful > > events (e.g. FAN_ACCESS*), but there is no need to do that before > > we see concrete benchmark results. > > OK, I think this idea is sound, I'd just be interested whether the 0-day > bot (or somebody else) is able to see improvement with this. Otherwise why > bother :) > Exactly. > > Jan, > > > > Whenever you have the time, feel free to see if this is a valid direction, > > if not for the perf optimization then we are going to need the > > fsnotify_sb_connector container for other features as well. > > So firstly the name fsnotify_sb_connector really confuses me. I'd save > "connector" names to fsnotify_mark_connector. Maybe fsnotify_sb_info? > Sure. > Then I dislike how we have to specialcase superblock in quite a few places > and add these wrappers and what not. This seems to be mostly caused by the > fact that you directly embed fsnotify_mark_connector into fsnotify_sb_info. > What if we just put fsnotify_connp_t there? I understand that this will > mean one more pointer fetch if there are actually marks attached to the > superblock and the event mask matches s_fsnotify_mask. But in that case we > are likely to generate the event anyway so the cost of that compared to > event generation is negligible? > I guess that can work. I can try it and see if there are any other complications. > And I'd allocate fsnotify_sb_info on demand from fsnotify_add_mark_locked() > which means that we need to pass object pointer (in the form of void *) > instead of fsnotify_connp_t to various mark adding functions (and transform > it to fsnotify_connp_t only in fsnotify_add_mark_locked() after possibly > setting up fsnotify_sb_info). Passing void * around is not great but it > should be fairly limited (and actually reduces the knowledge of fsnotify > internals outside of the fsnotify core). Unless I am missing something, I think we only need to pass an extra sb arg to fsnotify_add_mark_locked()? and it does not sound like a big deal. For adding an sb mark, connp arg could be NULL, and then we get connp from sb->fsnotify_sb_info after making sure that it is allocated. I will get to look at it in ~2 weeks. Thanks for the quick feedback. Amir.
