Bugzilla

Note, negative dcache entries can be tracked on a modern Linux kernel via /proc/sys/fs/dentry-state
```
# cat /proc/sys/fs/dentry-state
690051	666440	45	0	29022	0

dentry-state
------------

From linux/include/linux/dcache.h::

  struct dentry_stat_t dentry_stat {
        int nr_dentry;
        int nr_unused;
        int age_limit;         /* age in seconds */
        int want_pages;        /* pages requested by system */
        int nr_negative;       /* # of unused negative dentries */
        int dummy;             /* Reserved for future use */
  };
```
Dentries are dynamically allocated and deallocated.

nr_dentry shows the total number of dentries allocated (active + unused). nr_unused shows the number of dentries that are not actively used, but are saved in the LRU list for future reuse.

Age_limit is the age in seconds after which dcache entries can be reclaimed when memory is short and want_pages is nonzero when shrink_dcache_pages() has been called and the dcache isn't pruned yet.

nr_negative shows the number of unused dentries that are also negative dentries which do not map to any files. Instead, they help speeding up rejection of non-existing files provided by the users.