Date: Wed, 17 Sep 2008 09:59:48 -0700 From: Jason Evans <jasone@FreeBSD.org> To: Andrew MacIntyre <andymac@bullseye.apana.org.au> Cc: freebsd-hackers@freebsd.org Subject: Re: unexpected behaviour of malloc() on 7.0/amd64 Message-ID: <48D13784.2090701@FreeBSD.org> In-Reply-To: <48D12AD4.1000806@bullseye.andymac.org> References: <48D12AD4.1000806@bullseye.andymac.org>
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Andrew MacIntyre wrote:
> In investigating a Python 2.6rc1 regression test failure on FreeBSD
> 7.0/amd64, as far as I can tell, malloc() does not return NULL when
> available memory (including swap) is exhausted - the process just gets
> KILLed.
>
> Using ulimit -v to set a virtual memory use limit below the available
> memory does result in malloc() returning NULL when the limit is hit.
>
> The Python regression test concerned does not fail on FreeBSD 7.0/i386,
> however the C program below exhibits the unexpected behaviour on both
> 7.0/amd64 and 7.0/i386. The C program below does behave as
> expected on FreeBSD 6.3/i386; I cannot currently test its behaviour on
> FreeBSD 6.3/amd64.
>
> I can't see this behaviour documented in the malloc() man page.
From malloc(3):
===
IMPLEMENTATION NOTES
Traditionally, allocators have used sbrk(2) to obtain memory,
which is suboptimal for several reasons, including race conditions,
increased fragmentation, and artificial limitations on maximum usable
memory. This allocator uses both sbrk(2) and mmap(2) by default, but it
can be configured at run time to use only one or the other. If resource
limits are not a primary concern, the preferred configuration is
MALLOC_OPTIONS=dM or MALLOC_OPTIONS=DM. When so configured, the
datasize resource limit has little practical effect for typical
applications; use MALLOC_OPTIONS=Dm if that is a concern. Regardless of
allocator configuration, the vmemoryuse resource limit can be used to
bound the total virtual memory used by a process, as described in limits(1).
===
If you want a custom python binary that does not use mmap, you can
define _malloc_options to "d", or just use MALLOC_OPTIONS in the
environment.
Jason
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