On 07/28/2015 01:17 PM, Michal Hocko wrote:

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

On Mon 27-07-15 10:54:09, Eric B Munson wrote:

quoted

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.

quoted

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:
mlockall(MCL_CURRENT | MCL_ONFAULT);

To mlock future on fault only:
mlockall(MCL_FUTURE | MCL_ONFAULT);

To lock everything on fault:
mlockall(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT);

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?

munlock(all) already lost both MLOCK_LOCKED and MLOCK_ONFAULT flags in 
this revision, so I suppose in the next revision it will also not accept 
MLOCK_ONFAULT, and will just munlock whatever was mlocked in either mode.

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.

The effect of munlockall(MCL_FUTURE|MLOCK_ONFAULT), which you probably 
intended for converting the onfault to full prepopulation for future 
mappings, can be achieved by calling mlockall(MCL_FUTURE) (without 
MLOCK_ONFAULT).

Anyway munlock with flags opens new doors of trickiness.