On Fri 28-08-15 16:31:30, Michal Hocko wrote:

On Wed 26-08-15 14:24:23, Eric B Munson wrote:

quoted

The previous patch introduced a flag that specified pages in a VMA
should be placed on the unevictable LRU, but they should not be made
present when the area is created.  This patch adds the ability to set
this state via the new mlock system calls.

We add MLOCK_ONFAULT for mlock2 and MCL_ONFAULT for mlockall.
MLOCK_ONFAULT will set the VM_LOCKONFAULT modifier for VM_LOCKED.
MCL_ONFAULT should be used as a modifier to the two other mlockall
flags.  When used with MCL_CURRENT, all current mappings will be marked
with VM_LOCKED | VM_LOCKONFAULT.  When used with MCL_FUTURE, the
mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.  When used
with both MCL_CURRENT and MCL_FUTURE, all current mappings and
mm->def_flags will be marked with VM_LOCKED | VM_LOCKONFAULT.

Prior to this patch, mlockall() will unconditionally clear the
mm->def_flags any time it is called without MCL_FUTURE.  This behavior
is maintained after adding MCL_ONFAULT.  If a call to
mlockall(MCL_FUTURE) is followed by mlockall(MCL_CURRENT), the
mm->def_flags will be cleared and new VMAs will be unlocked.  This
remains true with or without MCL_ONFAULT in either mlockall()
invocation.

Btw. I think we really want a man page for this new mlock call.
-- 
Michal Hocko
SUSE Labs