On Thu, Feb 15, 2024 at 10:36 AM Jan Kara <jack@xxxxxxx> wrote: > > On Wed 14-02-24 15:40:31, Amir Goldstein wrote: > > > > > > 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. > ... > > > > 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. > > Yes that would be another possibility but frankly I like passing the > 'object' pointer instead of connp pointer a bit more. But we can see how > the code looks like. Ok, here it is: https://github.com/amir73il/linux/commits/fsnotify-sbinfo/ I agree that the interface does end up looking better this way. I've requested to re-test performance on fsnotify-sbinfo. You can use this rebased branch to look at the diff from the the previous patches that were tested by 0day: https://github.com/amir73il/linux/commits/fsnotify-sbconn/ If you have the bandwidth to consider those patches as candidates for (the second half of?) 6.9 merge window, I can post them for review. The main benefit of getting them merged in 6.9 is that I could work on pre-content events for 6.10 without having to worry about perf regressions. Thanks, Amir.
