On Sat 09-06-18 11:00:17, Amir Goldstein wrote: > On Sat, Jun 9, 2018 at 9:57 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > The only code that needs to test the shadow mask before following into > > connector is the optimization code in start of fsnotify() which was not > > generalized anyway and where the mask optimization is more important > > for mount watches. > > > > No. That's not true, there is also fsnotify_inode_watches_children() and > __fsnotify_parent(). But I think the only bits in the mask that really matter > for optimizing inode watches are FS_ACCESS and FS_EVENT_ON_CHILD > and those could be encoded in lower bits of connector pointer. Actually for children events, we have a dentry flag DCACHE_FSNOTIFY_PARENT_WATCHED and that should catch 99% of situation. FS_EVENT_ON_CHILD is used only to verify event really should be delivered since the DCACHE_FSNOTIFY_PARENT_WATCHED flag is cleared lazily. Or where do you think the performance of FS_EVENT_ON_CHILD checking matters? Also I'm not 100% sure just having FS_ACCESS checked quickly is going to buy us that much. We have quite a few event types and if someone is watching for a different event type than the current event (just not FS_ACCESS), we'll just have to pay the cost of srcu_read_lock and indirection. So it just depends whether we consider such loads worthwhile or not... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
