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

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH V5 0/7] Allow user to request memory to be locked on page fault
Date	2015-07-28 13:20 +0200
Message-ID	<pRb5p-7Bt-47@gated-at.bofh.it> (permalink)
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[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:
> 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?

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
SUSE Labs
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Re: [PATCH V5 0/7] Allow user to request memory to be locked on page  fault Eric B Munson <emunson@akamai.com> - 2015-07-27 15:40 +0200
  Re: [PATCH V5 0/7] Allow user to request memory to be locked on page  fault Vlastimil Babka <vbabka@suse.cz> - 2015-07-27 16:20 +0200
    Re: [PATCH V5 0/7] Allow user to request memory to be locked on page  fault Eric B Munson <emunson@akamai.com> - 2015-07-27 17:00 +0200
      Re: [PATCH V5 0/7] Allow user to request memory to be locked on page  fault Michal Hocko <mhocko@kernel.org> - 2015-07-28 13:20 +0200

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