Re: malloc() exceeds RLIMIT_DATA

[Graham Percival <gperciva%tarsnap.com@localhost>]

On Tue, Jul 09, 2019 at 07:17:39AM +0200, Martin Husemann wrote:
> The classical "data segment" (limited by RLIMIT_DATA) is not used much
> nowadays in NetBSD. Especially malloc() does not use it.
> 
>      RLIMIT_DATA     The maximum size (in bytes) of the data segment for a
>                      process; this defines how far a program may extend its
>                      break with the sbrk(2) system call.
> 
> 
> In ancient times malloc allocated memory via sbrk(2), but nowadays it uses
> mmap(2) with anonymous memory.

I have no complaint about the internal implementation of malloc().  But POSIX
says that:

    RLIMIT_DATA
    This is the maximum size of a data segment of the process, in bytes. If
    this limit is exceeded, the malloc() function shall fail with errno set to
    [ENOMEM].
    http://pubs.opengroup.org/onlinepubs/9699919799/functions/getrlimit.html

The relevant part is the second sentence.  My interpretation of that sentence
is that if malloc() does *not* fail when it is asked to exceed RLIMIT_DATA,
then it is not following the POSIX standard.

(In other communication, Colin Percival says that FreeBSD uses jemalloc, and
RLIMIT_DATA doesn't affect it, and that "... we should probably fix that some
day".  But since FreeBSD's RLIMIT_DATA is set to a much larger value than
NetBSD (256 MB for rlim_cur), nobody noticed.)

Cheers,
- Graham