On Sat 19-09-15 16:05:12, Tetsuo Handa wrote:
> Well, this seems to be a problem which prevents me from testing various
> patches that tries to address OOM livelock problem.
>
> ---------- rcu-stall.c start ----------
> #define _GNU_SOURCE
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sched.h>
>
> static int dummy(void *fd)
> {
> char c;
> /* Wait until the first child thread is killed by the OOM killer. */
> read(* (int *) fd, &c, 1);
> /* Try to consume as much CPU time as possible via preemption. */
> while (1);
You would kill the system by this alone. Having 1000 busy loops just
kills your machine from doing anything useful and you are basically
DoS-ed. I am not sure sprinkling preempt_{enable,disable} all around the
oom path makes much difference. If anything having a kernel high
priority kernel thread sounds like a better approach.
[...]
> for (i = 0; i < 1000; i++) {
> clone(dummy, malloc(1024) + 1024, CLONE_SIGHAND | CLONE_VM,
> &pipe_fd[0]);
> if (!i)
> close(pipe_fd[1]);
--
Michal Hocko
SUSE Labs
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