On Mon, 2 Jul 2018 12:34:00 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, Jul 1, 2018 at 10:52 PM Waiman Long <longman@xxxxxxxxxx> wrote: > > > > A rogue application can potentially create a large number of negative > > dentries in the system consuming most of the memory available if it > > is not under the direct control of a memory controller that enforce > > kernel memory limit. > > I certainly don't mind the patch series, but I would like it to be > accompanied with some actual example numbers, just to make it all a > bit more concrete. > > Maybe even performance numbers showing "look, I've filled the dentry > lists with nasty negative dentries, now it's all slower because we > walk those less interesting entries". > (Please cc linux-mm@xxxxxxxxx on this work) Yup. The description of the user-visible impact of current behavior is far too vague. In the [5/6] changelog it is mentioned that a large number of -ve dentries can lead to oom-killings. This sounds bad - -ve dentries should be trivially reclaimable and we shouldn't be oom-killing in such a situation. Dumb question: do we know that negative dentries are actually worthwhile? Has anyone checked in the past couple of decades? Perhaps our lookups are so whizzy nowadays that we don't need them?
