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    SubjectA question about page caching
    Hi folks,

    I have a little question about such thing as a page caching while file
    reading. As I know there is mechanism that optimise system performance
    when file read occurs repeatedly. But I can't simulate it. The test
    program that I wrote doesn't show acceptable results.
    Here is it.

    --- [main.c] ---
    #include <stdio.h>
    #include <fcntl.h>
    #include <stdlib.h>
    #include <asm/msr.h>

    #define RSIZE (4096*1024*128)

    int main()
    {
    int fd;
    char * data;
    unsigned long long counter0;
    unsigned long long counter1;

    fd = open("junkfile", O_RDONLY);
    if (fd == -1) {
    printf("ERROR: open() = %d\n", fd);
    exit(1);
    }

    data = (char *)malloc(RSIZE);
    if (data == NULL) {
    printf("ERROR: malloc() fails\n");
    exit(1);
    }

    rdtscll(counter0);
    read(fd, (void *)data, RSIZE);
    rdtscll(counter1);

    printf("D = %lu\n", counter1 - counter0);

    fgetc(stdin);

    close(fd);

    return 0;
    }
    --- [main.c] ---

    When I run first copy of program I have such result:
    (1) D = 191860948
    When I run second copy of program (i.e. when first copy waits on
    fgetc()) I have the similar result:
    (2) D = 192320613

    Where I be wrong?

    Thanks!


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