[PATCH V3 3/5] mm: mlock: Introduce VM_LOCKONFAULT and add mlock flags to enable it
corbet at lwn.net
Thu Jul 9 07:17:50 AEST 2015
On Wed, 8 Jul 2015 16:34:56 -0400
Eric B Munson <emunson at akamai.com> wrote:
> > Quick, possibly dumb question: I've been beating my head against these for
> > a little bit, and I can't figure out what's supposed to happen in this
> > case:
> > mlock2(addr, len, MLOCK_ONFAULT);
> > munlock2(addr, len, MLOCK_LOCKED);
> > It looks to me like it will clear VM_LOCKED without actually unlocking any
> > pages. Is that the intended result?
> This is not quite right, what happens when you call munlock2(addr, len,
> MLOCK_LOCKED); is we call apply_vma_flags(addr, len, VM_LOCKED, false).
From your explanation, it looks like what I said *was* right...what I was
missing was the fact that VM_LOCKED isn't set in the first place. So that
call would be a no-op, clearing a flag that's already cleared.
One other question...if I call mlock2(MLOCK_ONFAULT) on a range that
already has resident pages, I believe that those pages will not be locked
until they are reclaimed and faulted back in again, right? I suspect that
could be surprising to users.
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