On Thu, Sep 05, 2013 at 12:03:03PM -0500, Malahal Naineni wrote: > Neil Brown posted a patch couple days ago for this! > > http://thread.gmane.org/gmane.linux.nfs/58473 I tried Neil's patch on a v3.11 kernel. The rebuilt kernel still exhibited the same 1000s of WRITEs/sec problem. Any other ideas? > Regards, Malahal. > > Quentin Barnes [qbarnes@xxxxxxxxx] wrote: > > If two (or more) processes are doing nothing more than writing to > > the memory addresses of an mmapped shared file on an NFS mounted > > file system, it results in the kernel scribbling WRITEs to the > > server as fast as it can (1000s per second) even while no syscalls > > are going on. > > > > The problems happens on NFS clients mounting NFSv3 or NFSv4. I've > > reproduced this on the 3.11 kernel, and it happens as far back as > > RHEL6 (2.6.32 based), however, it is not a problem on RHEL5 (2.6.18 > > based). (All x86_64 systems.) I didn't try anything in between. > > > > I've created a self-contained program below that will demonstrate > > the problem (call it "t1"). Assuming /mnt has an NFS file system: > > > > $ t1 /mnt/mynfsfile 1 # Fork 1 writer, kernel behaves normally > > $ t1 /mnt/mynfsfile 2 # Fork 2 writers, kernel goes crazy WRITEing > > > > Just run "watch -d nfsstat" in another window while running the two > > writer test and watch the WRITE count explode. > > > > I don't see anything particularly wrong with what the example code > > is doing with its use of mmap. Is there anything undefined about > > the code that would explain this behavior, or is this a NFS bug > > that's really lived this long? > > > > Quentin > > > > > > > > #include <sys/stat.h> > > #include <sys/mman.h> > > #include <sys/stat.h> > > #include <sys/wait.h> > > #include <errno.h> > > #include <fcntl.h> > > #include <stdio.h> > > #include <stdlib.h> > > #include <signal.h> > > #include <string.h> > > #include <unistd.h> > > > > int > > kill_children() > > { > > int cnt = 0; > > siginfo_t infop; > > > > signal(SIGINT, SIG_IGN); > > kill(0, SIGINT); > > while (waitid(P_ALL, 0, &infop, WEXITED) != -1) ++cnt; > > > > return cnt; > > } > > > > void > > sighandler(int sig) > > { > > printf("Cleaning up all children.\n"); > > int cnt = kill_children(); > > printf("Cleaned up %d child%s.\n", cnt, cnt == 1 ? "" : "ren"); > > > > exit(0); > > } > > > > int > > do_child(volatile int *iaddr) > > { > > while (1) *iaddr = 1; > > } > > > > int > > main(int argc, char **argv) > > { > > const char *path; > > int fd; > > ssize_t wlen; > > int *ip; > > int fork_count = 1; > > > > if (argc == 1) { > > fprintf(stderr, "Usage: %s {filename} [fork_count].\n", > > argv[0]); > > return 1; > > } > > > > path = argv[1]; > > > > if (argc > 2) { > > int fc = atoi(argv[2]); > > if (fc >= 0) > > fork_count = fc; > > } > > > > fd = open(path, O_CREAT|O_TRUNC|O_RDWR|O_APPEND, S_IRUSR|S_IWUSR); > > if (fd < 0) { > > fprintf(stderr, "Open of '%s' failed: %s (%d)\n", > > path, strerror(errno), errno); > > return 1; > > } > > > > wlen = write(fd, &(int){0}, sizeof(int)); > > if (wlen != sizeof(int)) { > > if (wlen < 0) > > fprintf(stderr, "Write of '%s' failed: %s (%d)\n", > > path, strerror(errno), errno); > > else > > fprintf(stderr, "Short write to '%s'\n", path); > > return 1; > > } > > > > ip = (int *)mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, > > MAP_SHARED, fd, 0); > > if (ip == MAP_FAILED) { > > fprintf(stderr, "Mmap of '%s' failed: %s (%d)\n", > > path, strerror(errno), errno); > > return 1; > > } > > > > signal(SIGINT, sighandler); > > > > while (fork_count-- > 0) { > > switch(fork()) { > > case -1: > > fprintf(stderr, "Fork failed: %s (%d)\n", > > strerror(errno), errno); > > kill_children(); > > return 1; > > case 0: /* child */ > > signal(SIGINT, SIG_DFL); > > do_child(ip); > > break; > > default: /* parent */ > > break; > > } > > } > > > > printf("Press ^C to terminate test.\n"); > > pause(); > > > > return 0; > > } > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > Quentin -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
