The number of negative dentries is effectively constrained only by memory size. Systems which do not experience significant memory pressure for an extended period can build up millions of negative dentries which clog the dcache. That can have different symptoms, such as inotify taking a long time [1], high memory usage [2] and even just poor lookup performance [3]. We've also seen problems with cgroups being pinned by negative dentries, though I think we now reparent those dentries to their parent cgroup instead. We don't have a really good solution yet, and maybe some focused brainstorming on the problem would lead to something that actually works. (Apologies to Stephen; I should have thought to send this before the invitations to LSFMM went out). [1] https://lore.kernel.org/linux-fsdevel/20220209231406.187668-1-stephen.s.brennan@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-fsdevel/1611235185-1685-1-git-send-email-gautham.ananthakrishna@xxxxxxxxxx/ [3] https://lore.kernel.org/linux-fsdevel/158893941613.200862.4094521350329937435.stgit@buzz/
