Re: Subtle MM bug

[Szabolcs Szakacsits]

Andi Kleen <[e-mail]> wrote:
> On Sun, Jan 07, 2001 at 09:29:29PM -0800, Wayne Whitney wrote:
> > package called MAGMA; at times this requires very large matrices. The
> > RSS can get up to 870MB; for some reason a MAGMA process under linux
> > thinks it has run out of memory at 870MB, regardless of the actual
> > memory/swap in the machine. MAGMA is single-threaded.
> I think it's caused by the way malloc maps its memory.
> Newer glibc should work a bit better by falling back to mmap even
> for smaller allocations (older does it only for very big ones)

AFAIK newer glibc = CVS glibc but the malloc() tune parameters
work via environment variables for the current stable ones as well,
e.g. to overcome the above "out of memory" one could do,
% export MALLOC_MMAP_MAX_=1000000
% export MALLOC_MMAP_THRESHOLD_=0
% magma

At default, on a 32bit Linux current stable glibc malloc uses brk
between 0x08??????-0x40000000 and max (MALLOC_MMAP_MAX_) 128 mmap if
the requested chunk is greater than 128 kB (MALLOC_MMAP_THRESHOLD_).
If MAGMA mallocs memory in less than 128 kB chunks then the above out
of memory behaviour is expected.

	Szaka