Bug 97233

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Description of problem:
On a machine (compaq dl380 G-3) with 4 gB RAM, trying to malloc 2 gB of RAM with
bigpages enabled locks up at about 1.4 gB, though it eventually finishes in
50-70 seconds.

After disabling bigpages feature, the operation completes successfully in about
6 seconds, the same time as on non-bigpages-capable distributions (RH 7.x/8.0/9).

oracle and redhat recommend using bigpages to enhance oracle performance in
these docs:

http://www.redhat.com/whitepapers/rhel/OracleLinuxInstallTips.pdf
http://otn.oracle.com/tech/linux/pdf/1_linuxVM_v2_accepted.pdf

Version-Release number of selected component (if applicable):
2.4.9-e.24 and all other kernels

How reproducible:
Always

Steps to Reproduce:
1. intall stock RHAS on machine with 4 gB of RAM.
2. upgrade to e.24-enterprise kernel
3. add this line to rc.local:

## Bigpages -- check with 'cat /proc/meminfo'
echo 2 > /proc/sys/kernel/shm-use-bigpages      ## bigpages in shmfs

4. add this line to /etc/lilo.conf for the kernel you're going to boot:

        append="bigpages=2100MB"

5. run lilo ('lilo -v')
6. reboot
7. compile the attached source (gcc -o /usr/local/bin/slurpmem slurpmem.c)
8. run slurpmem like this: 'slurpmem 2000', which attempts to allocated 2 gB of
RAM via malloc system call.
9. box will freeze at about 1.5 gB, taking about 50 seconds to allocate RAM.

control case:
1. comment out the "append=" line in lilo.conf from step 4. above.
2. run lilo & reboot
3. repeat step 8.


Actual Results:  severe lock-up after about 1.4 gB of allocation

Expected Results:  no lock-up

Additional info:

Here's the c program that we use to reproduce the problem:

#include <stdio.h>
#include <string.h>

#define MEG ( 1024 * 1024 )


int main(int argc, char **argv) {

        char    **stored;
        int     megs;
        int i;


        if ( argc < 1 ) {

                printf("No argument specified.\n");
                exit(1);

        }

        megs = atoi(argv[1]);

        printf("%d megabytes will be slurped\n", megs);

        stored = (char **) malloc( sizeof( char* ) * megs );

        if ( stored < 0 ) {

                perror("malloc");
                exit(1);
        }

        printf("Megs zeroed: ");

        for ( i = 0; i < megs; i++ ) {

                stored[i] = (char *) malloc( MEG );

                if ( stored[i] < 0 ) {
                        perror("malloc");
                        exit(1);
                }

                memset( stored[i], 0, MEG - 1);

                printf("%d ", i);

        }

        printf("\n\n");
        printf("All alocated!\n");
        printf("Waiting for <control-c> to finish\n");
        scanf("%d", &i);

        exit(0);
}