Jason Evans wrote:
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.
Thanks for the reply. The malloc(3) man page for 7.0 doesn't include
this information, and says sbrk() is only used on i386.
From the 7-stable version of the man page, which appears to match your
quote above, I infer that these changes will be in 7.1.
However my reading of the updated man page suggests that the malloc
options string should be "Dm" or "m" to turn off mmap() and only use
sbrk() - could you clarify why "d"?
Thanks,
Andrew.
--
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