Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> When oom_reaper manages to unmap all the eligible vmas there shouldn't
> be much of the freable memory held by the oom victim left anymore so it
> makes sense to clear the TIF_MEMDIE flag for the victim and allow the
> OOM killer to select another task.
Just a confirmation. Is it safe to clear TIF_MEMDIE without reaching do_exit()
with regard to freezing_slow_path()? Since clearing TIF_MEMDIE from the OOM
reaper confuses
wait_event(oom_victims_wait, !atomic_read(&oom_victims));
in oom_killer_disable(), I'm worrying that the freezing operation continues
before the OOM victim which escaped the __refrigerator() actually releases
memory. Does this cause consistency problem?
> + /*
> + * Clear TIF_MEMDIE because the task shouldn't be sitting on a
> + * reasonably reclaimable memory anymore. OOM killer can continue
> + * by selecting other victim if unmapping hasn't led to any
> + * improvements. This also means that selecting this task doesn't
> + * make any sense.
> + */
> + tsk->signal->oom_score_adj = OOM_SCORE_ADJ_MIN;
> + exit_oom_victim(tsk);
I noticed that updating only one thread group's oom_score_adj disables
further wake_oom_reaper() calls due to rough-grained can_oom_reap check at
p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN
in oom_kill_process(). I think we need to either update all thread groups'
oom_score_adj using the reaped mm equally or use more fine-grained can_oom_reap
check which ignores OOM_SCORE_ADJ_MIN if all threads in that thread group are
dying or exiting.
----------
#define _GNU_SOURCE
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sched.h>
static int writer(void *unused)
{
static char buffer[4096];
int fd = open("/tmp/file", O_WRONLY | O_CREAT | O_APPEND, 0600);
while (write(fd, buffer, sizeof(buffer)) == sizeof(buffer));
return 0;
}
int main(int argc, char *argv[])
{
unsigned long size;
char *buf = NULL;
unsigned long i;
if (fork() == 0) {
int fd = open("/proc/self/oom_score_adj", O_WRONLY);
write(fd, "1000", 4);
close(fd);
for (i = 0; i < 2; i++) {
char *stack = malloc(4096);
if (stack)
clone(writer, stack + 4096, CLONE_VM, NULL);
}
writer(NULL);
while (1)
pause();
}
sleep(1);
for (size = 1048576; size < 512UL * (1 << 30); size <<= 1) {
char *cp = realloc(buf, size);
if (!cp) {
size >>= 1;
break;
}
buf = cp;
}
sleep(5);
/* Will cause OOM due to overcommit */
for (i = 0; i < size; i += 4096)
buf[i] = 0;
pause();
return 0;
}
----------
----------
[ 177.722853] a.out invoked oom-killer: gfp_mask=0x24280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), order=0, oom_score_adj=0
[ 177.724956] a.out cpuset=/ mems_allowed=0
[ 177.725735] CPU: 3 PID: 3962 Comm: a.out Not tainted 4.5.0-rc2-next-20160204 #291
(...snipped...)
[ 177.802889] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
(...snipped...)
[ 177.872248] [ 3941] 1000 3941 28880 124 14 3 0 0 bash
[ 177.874279] [ 3962] 1000 3962 541717 395780 784 6 0 0 a.out
[ 177.876274] [ 3963] 1000 3963 1078 21 7 3 0 1000 a.out
[ 177.878261] [ 3964] 1000 3964 1078 21 7 3 0 1000 a.out
[ 177.880194] [ 3965] 1000 3965 1078 21 7 3 0 1000 a.out
[ 177.882262] Out of memory: Kill process 3963 (a.out) score 998 or sacrifice child
[ 177.884129] Killed process 3963 (a.out) total-vm:4312kB, anon-rss:84kB, file-rss:0kB, shmem-rss:0kB
[ 177.887100] oom_reaper: reaped process :3963 (a.out) anon-rss:0kB, file-rss:0kB, shmem-rss:0lB
[ 179.638399] crond invoked oom-killer: gfp_mask=0x24201ca(GFP_HIGHUSER_MOVABLE|__GFP_COLD), order=0, oom_score_adj=0
[ 179.647708] crond cpuset=/ mems_allowed=0
[ 179.652996] CPU: 3 PID: 742 Comm: crond Not tainted 4.5.0-rc2-next-20160204 #291
(...snipped...)
[ 179.771311] [ pid ] uid tgid total_vm rss nr_ptes nr_pmds swapents oom_score_adj name
(...snipped...)
[ 179.836221] [ 3941] 1000 3941 28880 124 14 3 0 0 bash
[ 179.838278] [ 3962] 1000 3962 541717 396308 785 6 0 0 a.out
[ 179.840328] [ 3963] 1000 3963 1078 0 7 3 0 -1000 a.out
[ 179.842443] [ 3965] 1000 3965 1078 0 7 3 0 1000 a.out
[ 179.844557] Out of memory: Kill process 3965 (a.out) score 998 or sacrifice child
[ 179.846404] Killed process 3965 (a.out) total-vm:4312kB, anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
----------
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