On Fri, 11 Apr 2025 at 16:47, Christian Brauner <brauner@xxxxxxxxxx> wrote: > Note that we have a new sysctl: > > /proc/sys/fs/dentry-negative > > that can be used to control the negative dentry policy because any > generic change that we tried to make has always resulted in unacceptable > regressions for someone's workload. Currently we only allow it to be set > to 1 (default 0). If set to 1 it will not create negative dentries > during unlink. If that's sufficient than recommend this to users that > suffer from this problem if not consider adding another sensitive > policy. Okay, I'll forward that info. However, hundreds of millions of negative dentries can be created rather efficiently without unlink, though this one probably doesn't happen under normal circumstances. Allowing this to starve the scheduler for an arbitrary long time is not a good idea in any case, so the fsnotify problem needs some other solution, and I suspect that it's not to disable negative caching completely, as that would be a major bummer. But the idea of leaving negative dentries off d_children is independent of caching policy. The lookup cache would work fine without d_sib being chained, it only needs careful thought in 1) putting the dentry on d_children when it's turned into positive 2) getting the dentry off d_children when it's turned into negative. Thanks, Miklos
