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

[Andrea Arcangeli]

On Sat, Jan 12, 2002 at 05:07:42PM +0100, Manfred Spraul wrote:
> Andi Kleen wrote:
> > 
> > For the stack they can get minor faults anyways when they allocate new
> > stack space below ESP. There is no good way to fix that from the kernel; the
> > application has to preallocate its memory on stack. I think it's reasonable
> > if it does the same for holes on the stack.
> >
> Ok, everyone agrees that mlockall() should not grow VM_GROWSDOWN
> segments to their maximum size.

Ah, definitely. I must have misunderstood something in the discussion
sorry, I thought we were just discussiong the below issue, and I
completly missed the "maximum size" one.

All I was trying to find out here, was about the intermediate pages
between vm_start and vm_end of a VM_GROWSDOWN|VM_LOCKED vma, exactly
your example below.

> Should the page fault handler fill the hole created by
> 
> void * grow_stack(void)
> {
> 	char data[100000];
> 	data[0] = '0';
> 	return data;
> }
> 
> The principle of least surprise would mean filling holes, but OTHO sane
> apps would use memset(data,0,sizeof(data)).

yep.

Andrea