mcs.c

// make mcs; ./mcs file
// writes <sample size> as uint32 to mincore.bin followed by 1 mincore() per second for 60 seconds

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#define CHECK(x) if ((x) == -1) { perror(#x); err = 1; goto cleanup; }
#define USEC_PER_SEC 1000000

int main(int argc, char **argv) {
    int err = 0;
    if (argc < 2) {
        printf("Usage: %s <filename>", argv[0]);
    }
    int fd = open(argv[1], O_RDONLY);
    struct stat statbuf;
    CHECK(fstat(fd, &statbuf));
    void* mapping = mmap(NULL, statbuf.st_size, PROT_READ, MAP_SHARED, fd, 0);
    if (mapping == NULL) {
        perror("mmap");
        err = 1;
        goto cleanup;
    }
    int pagesize = 4096;
    FILE* outf = fopen("mincore.bin", "w");
    if (outf==NULL) {
        perror("fopen");
        err = 1;
        goto cleanup;
    }
    uint32_t mcbuflen = (statbuf.st_size + pagesize -1 ) / pagesize;
    fwrite(&mcbuflen, sizeof(mcbuflen), 1, outf);
    int steps = 60;
    void* mcorebuf = malloc(mcbuflen);
    for (int i=0; i<steps; i++) {
        mincore(mapping, statbuf.st_size, mcorebuf);
        fwrite(mcorebuf, mcbuflen, 1, outf);
        usleep(USEC_PER_SEC);
    }
    cleanup:
    fclose(outf);
    free(mcorebuf);
    return err;
}

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