Including contigmem in core dumps

[Dmitry Kozlyuk]

2024-10-22 07:41 (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()? 

The commit that originally added madvise() argued that dumping everything
ended up in coredumps with "useless" data [non-mapped or unused pages]:

http://git.dpdk.org/dpdk/commit/?id=d72e4042c5ebda7af81448b387af8218136402d0

Dumping mapped pages sounds reasonable in many cases.
Not in all cases admittedly:
- legacy memory mode mapping a lot of pages that are not (yet) used;
- if packet data is confidential while the app is not.

The option to dump or not can easily be a runtime one.
The safe default however seems to be "off".

In dynamic memory node (not FreeSBD, unfortunately)
rte_mem_event_callback-register() may be used to call madvise().
Maybe DPDK should allow such callbacks in any mode
and invoke them during initialization to make the above solution universal.