On 03/03, KOSAKI Motohiro wrote:
>
> > By iterating over threads instead, it is possible to detect threads that
> > are exiting and nominate them for oom kill so they get access to memory
> > reserves.
>
> In fact, PF_EXITING is a sing of *THREAD* exiting, not process. Therefore
> PF_EXITING is not a sign of memory freeing in nearly future. If other
> CPUs don't try to free memory, prevent oom and waiting makes deadlock.
I agree. I don't understand this patch.
And. Instead of moving to for_each_mm() this patch moves the logic back,
to for_each_thread().
> Thus, I suggest to remove PF_EXITING check completely.
Again, this seems better to me but I do not really understand oom
killer's heuristic. Perhaps this check helps with some workloads.
I tried to avoid this discussion because I have nothing new to add,
and the previous discussion was painful. But since this patch was
merged into -mm,
> > @@ -324,7 +324,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
> > * the process of exiting and releasing its resources.
> > * Otherwise we could get an easy OOM deadlock.
> > */
> > - if (thread_group_empty(p) && (p->flags & PF_EXITING) && p->mm) {
> > + if ((p->flags & PF_EXITING) && p->mm) {
The previous check was not perfect, we know this.
But with this patch applied, the simple program below disables oom-killer
completely. select_bad_process() can never succeed.
I think this patch should dropped. And another one,
oom-skip-zombies-when-iterating-tasklist.patch
should be dropped as well. Add Andrey.
Oleg.
#include <unistd.h>
#include <signal.h>
#include <pthread.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
void *tfunc(void* arg)
{
pause();
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t thread;
pthread_create(&thread, NULL, tfunc, NULL);
pthread_create(&thread, NULL, tfunc, NULL);
ptrace(PTRACE_TRACEME, 0,0,0);
kill(getpid(), SIGSTOP);
pthread_kill(thread, SIGQUIT);
pause();
return 0;
}
assert(wait(NULL) == pid);
assert(ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACEEXIT) == 0);
assert(ptrace(PTRACE_CONT, pid, 0, 0) == 0);
wait(NULL);
pause();
return 0;
}
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