Enable temporary caching of the last request_key() result


Linux Kernel Configuration
└─>Security options
└─>Enable temporary caching of the last request_key() result
In linux kernel since version 5.1 (release Date: 2019-05-05)  
This option causes the result of the last successful request_key()
call that didn't upcall to the kernel to be cached temporarily in the
task_struct. The cache is cleared by exit and just prior to the
resumption of userspace.

This allows the key used for multiple step processes where each step
wants to request a key that is likely the same as the one requested
by the last step to save on the searching.

An example of such a process is a pathwalk through a network
filesystem in which each method needs to request an authentication
key. Pathwalk will call multiple methods for each dentry traversed
(permission, d_revalidate, lookup, getxattr, getacl, ...).