[$] Dentry negativity

Back in 2017, Waiman Long posted a patchset placing limits on the number of "negative dentries" stored by thekernel. The better part of three years later, that work continues with,seemingly, no better prospects for getting into the mainline. It would beunderstandable, though, if many people out there don't really know whatnegative dentries are or why kernel developers care about them. That, atleast, can be fixed, even if the underlying problem seems to be moredifficult.