Re: How big should bigcore.core be?

[Ulrich Weigand <weigand at i1 dot informatik dot uni-erlangen dot de>]

Mark Kettenis wrote:

>If the latter is true, I really think we should disable this test by
>default and only enable it on systems where we know we won't generate
>ridiculously large files running the risk of crashing the machine.
>For my work on GDB, I regularly use machines that are not mine, and
>I'd really hate it if I crashed those.

As one data point, I can confirm from experience that bigcore can
crash an s390x-ibm-linux system hard (provided you run with memory
overcommit and no ulimits).

Cause of crash is that it allocates a couple of terabytes heap,
and then tries to coredump them; the Linux kernel coredump routines
do a full address space page-table walk, which insists on creating
all *page tables* visited, if not yet present.  For a couple of
terabytes address space, you need a couple of gigabytes page tables,
which are non-pagable kernel memory -- more real memory than my 
machine had ...

Now, running with overcommit and no ulimits on a 64-bit Linux 
machine is something you shouldn't do anyway, but it's still
not nice to hit this problem just from running the gdb test
suite :-/ 

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de