Re: Q: behaviour of mlockall(MCL_FUTURE) and VM_GROWSDOWN segments

[Andrew Morton <akpm@zip.com.au>]

Andi Kleen wrote:
> 
> Andrew Morton <akpm@zip.com.au> writes:
> 
> > So in this case, the behaviour I would prefer is MCL_FUTURE for
> > all vma's *except* the stack.   Stack pages should be locked
> > only when they are faulted in.   Hard call.
> 
> There is just one problem: linuxthread stacks are just ordinary mappings
> and they are in no way special to the kernel; they aren't VM_GROWSDOWN.
> You would need to add a way to the kernel first to tag the linux thread
> stacks in a way that is recognizable to mlockall and then do that
> from linuxthreads.
> 
> I think for the normal stack - real VM_GROWSDOWN segments - mlockall
> already does the right thing.

hmm.. So I wonder what changed between 2.4.7 and 2.4.15 which unbroke
MCL_FUTURE.

I suspect we can fix the problem by running mlockall(MCL_FUTURE)
and then an explicit munlock() of the stack area.

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