[$] Negative dentries, 20 years later

Filesystems and the virtual filesystem layer are in the business ofmanaging files that actually exist, but the Linux "dentry cache", whichremembers the results of file-name lookups, also keeps track of files thatdon't exist. This cache of "negative dentries" plays an importantrole in the overall performance of the system but, if it is allowed to growtoo large, its role can become negative in its own right. As the 2022 Linux Storage, Filesystem,and Memory-Management Summit (LSFMM) approaches, the subject of negativedentries has come up yet again; whether one can be positive about theprospects for a resolution this time around remains unclear.