On 07/21/2015 09:59 PM, Eric B Munson wrote:

With the refactored mlock code, introduce new system calls for mlock,
munlock, and munlockall.  The new calls will allow the user to specify
what lock states are being added or cleared.  mlock2 and munlock2 are
trivial at the moment, but a follow on patch will add a new mlock state
making them useful.

munlock2 addresses a limitation of the current implementation.  If a

   ^ munlockall2?

user calls mlockall(MCL_CURRENT | MCL_FUTURE) and then later decides
that MCL_FUTURE should be removed, they would have to call munlockall()
followed by mlockall(MCL_CURRENT) which could potentially be very
expensive.  The new munlockall2 system call allows a user to simply
clear the MCL_FUTURE flag.