Date: Sat, 11 Nov 2000 12:25:11 -0500 (EST) From: Mitch Collinsworth <mitch@ccmr.cornell.edu> To: freebsd-questions@freebsd.org Cc: Mitch Collinsworth <mitch@mercury.ccmr.cornell.edu> Subject: Linux malloc better on FreeBSD than FreeBSD malloc? Message-ID: <Pine.LNX.4.10.10011111153160.16421-100000@dragon.ccmr.cornell.edu>
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Well I hope that subject was provocative enough to generate some
interest! :-) Here's a strange situation that's bugging me. I
recently changed jobs, into a dept that's heavily Linux-based. I
of course have different preferences, but need to demonstrate
technical superiority if any changes are going to happen. An
opportunity just arose to make some comparisons between Linux and
FreeBSD in maximum process size. We have some new systems with
4 GB RAM each that will be made available for running large batch
jobs.
We have a very simple test program that malloc's successively larger
and larger blocks of memory until it fails, freeing the current blocks
after each successful trial. The strange thing is that the test
program runs much farther on FreeBSD using the Linux binary in
compatibility mode than it does using the binary compiled on FreeBSD!
Included below are the output from each binary and the source. Can
anyone explain these results?
A second question, which is the primary issue we were trying to
discover is if it is possible for a single process to malloc more than
2 GB of memory. FreeBSD supposedly supports up to 4 GB (on Intel
hardware), but does anyone know if there is still a 2 GB per process
limit? And if a single process can be larger than 2 GB, is there a
2 GB limit on any single malloc with that process?
For comparison purposes, the Linux answers to these questions are that
with a special "bigmem" patch installed, a process can be larger than
2 GB, but any single malloc is still limited to 2 GB.
The system the tests are being run on is a 900 MHz Xeon running
FreeBSD 4.1-R with 1 GB RAM and 18 GB swap:
ruby> swapinfo -k
Device 1K-blocks Used Avail Capacity Type
/dev/da0s3b 511872 0 511872 0% Interleaved
/dev/rda1c 17783108 0 17783108 0% Interleaved
Total 18294980 0 18294980 0%
------FreeBSD results---------
# with FreeBSD compiled binary
ruby> ./grab-fbsd
Allocated f 268435455
Punt g at 268435455
# with Linux compiled binary run in compatibility mode
ruby> ./grab-linux
Allocated f 268435455
Allocated g 268435455
Allocated f 536870911
Allocated g 536870911
Allocated f 805306367
Allocated g 805306367
Allocated f 1073741823
Allocated g 1073741823
Allocated f 1342177279
Punt g at 1342177279
------source-----------------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[]){
unsigned long i, s2;
char *foo, *goo;
for (i=1; i<100; i++){
foo = (char *) malloc(s2=(unsigned long)i*(1024*1024*256)-1);
if ( foo == NULL) {
printf("Punt f at %lu\n", s2);
exit(1);
} else {
printf("Allocated f %lu\n",s2);
}
goo = (char *) malloc(s2=(unsigned long)i*(1024*1024*256)-1);
if ( goo == NULL) {
printf("Punt g at %lu\n", s2);
exit(1);
} else {
printf("Allocated g %lu\n",s2);
}
sleep(4);
free(foo);
free(goo);
}
}
-----------------------------
Thanks for any help. Please cc: me on replies. I'm no longer getting
-questions directly.
-Mitch
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