about /proc/meminfo and mmap

From: Zhixu Liu (liuzx@bnl.gov)
Date: Fri Oct 20 2000 - 20:24:33 EDT

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    Hi, all:

    My PC have 128M RAM, but in /proc/meminfo, it display 122424K, not
    128*1024K = 131072K, what does this mean?

    My program need to a 32M buffer, so I add "append="mem=96M"" to lilo.conf,
    then the PC only know 96M mem, I can use the rest 32M. Following is a
    simple example:

    /****************************************************************/
     int fd = open("/dev/mem", O_RDWR);
     if (fd < 0) {
            printf("failed to open /dev/mem\n");
            return -1;
            }
     start = (DATA *) mmap(0, length*sizeof(DATA),PROT_READ|PROT_WRITE,
           MAP_SHARED, fd, BASE_ADDRESS);
     if (start == (DATA *) (-1) ) {
            printf("failed to map /dev/mem\n");
            return -1;
            }

     // do ...

     munmap(start, length);
     
    /****************************************************************/

    Is there some problem? Or does the DATA are all in real RAM? Any
    suggestions are welcome.

    Thanks a lot.

    Regards.

    Zhixu

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