On Fri, May 07, 2004 at 12:58:28AM +0200, Vincent Lefevre wrote:[...]
This is precisely what I thought to be the bug in glibc: the fact (at least with the 2.4 kernel) that this flag is used by glibc. On which documentation is glibc based (in particular, concerning old_mmap)?
I don't know. The comments suggest malloc made the choice deliberately, though, so I don't think it's appropriate to reverse it.
For what it's worth, this is in the malloc(3) manual page on my Debian/sarge system (from the package manpages-dev-1.66-1)
BUGS
By default, Linux follows an optimistic memory allocation strategy.
This means that when malloc() returns non-NULL there is no guarantee
that the memory really is available. This is a really bad bug. In case
it turns out that the system is out of memory, one or more processes
will be killed by the infamous OOM killer. In case Linux is employed
under circumstances where it would be less desirable to suddenly lose
some randomly picked processes, and moreover the kernel version is suf-
ficiently recent, one can switch off this overcommitting behavior using
a command like
# echo 2 > /proc/sys/vm/overcommit_memory
See also the kernel Documentation directory, files vm/overcommit-
accounting and sysctl/vm.txt.
If somebody would like to submit a patch to manpages-dev, I'm sure it would save grief for other developers to have it clearly spelled out that glibc's malloc() uses the MAP_NORESERVE flag when allocating memory. It would tell people what to look for when reading the kernel documentation referred to.
--Steve Augart
-- Steven Augart
Jikes RVM, a free, open source, Virtual Machine: http://oss.software.ibm.com/jikesrvm
