Question about freeing segments in non contiguous main_arena

[Florian Weimer]

* Abhijit Ray Chaudhury:

> Hi Florian,
>
> Thanks a lot for your reply. In the case of non-contiguous main_arena
> , assume the av->top points to a mmapped segment. Application started
> freeing the memory in the order of allocation . av->top starts getting
> adjusted .  Since it is not heap_info structure you don't know the
> base address of the segment. Would munmap be called ?
>
> If it is not called, would we leak the virtual address space ? How is
> the address space supported to be reclaimed ? Is it a bug then ?

This code path is mostly unused.  A mapping that acts as an obstraction
for sbrk is required.  Currently, MTE-enabled malloc on Arm uses this
code path, too.

We have a similar problems with heaps in the middle of arenas.  Tackling
that is probably more worthwhile.

Thanks,
Florian