Including contigmem in core dumps

[Dmitry Kozlyuk]

Hi Lewis,

2024-05-27 19:34 (UTC-0500), Lewis Donzis:
> I've been wondering why we exclude memory allocated by eal_get_virtual_area() from core dumps? (More specifically, it calls eal_mem_set_dump() to call madvise() to disable core dumps from the allocated region.) 
> 
> On many occasions, when debugging after a crash, it would have been very convenient to be able to see the contents of an mbuf or other object allocated in contigmem space. And we often avoid using the rte memory allocator just because of this. 
> 
> Is there any reason for this, or could it perhaps be a compile-time configuration option not to call madvise()? 

Memory reserved by eal_get_virtual_area() is not yet useful,
but it is very large, so by excluding it from dumps,
DPDK prevents dumps from including large zero-filled parts.

It also makes sense to call eal_mem_set_dump(..., false)
from eal_memalloc.c:free_seg(), because of --huge-unlink=never:
in this mode (Linux-only), freed segments are not cleared,
so if they were included into dump, it would be a lot of garbage data.

Newly allocated hugepages are not included into dumps
because this would make dumps very large by default.
However, this could be an opt-in as a runtime option if need be.