[PATCH V5 0/7] Allow user to request memory to be locked on page fault

Michal Hocko mhocko at kernel.org
Tue Jul 28 21:17:25 AEST 2015

[I am sorry but I didn't get to this sooner.]

On Mon 27-07-15 10:54:09, Eric B Munson wrote:
> Now that VM_LOCKONFAULT is a modifier to VM_LOCKED and
> cannot be specified independentally, it might make more sense to mirror
> that relationship to userspace.  Which would lead to soemthing like the
> following:

A modifier makes more sense.
> To lock and populate a region:
> mlock2(start, len, 0);
> To lock on fault a region:
> mlock2(start, len, MLOCK_ONFAULT);
> If LOCKONFAULT is seen as a modifier to mlock, then having the flags
> argument as 0 mean do mlock classic makes more sense to me.
> To mlock current on fault only:
> To mlock future on fault only:
> To lock everything on fault:

Makes sense to me. The only remaining and still tricky part would be
the munlock{all}(flags) behavior. What should munlock(MLOCK_ONFAULT)
do? Keep locked and poppulate the range or simply ignore the flag an
just unlock?

I can see some sense to allow munlockall(MCL_FUTURE[|MLOCK_ONFAULT]),
munlockall(MCL_CURRENT) resp. munlockall(MCL_CURRENT|MCL_FUTURE) but
other combinations sound weird to me.

Anyway munlock with flags opens new doors of trickiness.
Michal Hocko

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