exit: reparent: avoid find_new_reaper() if no children
Now that pid_ns logic was isolated we can change forget_original_parent()
to return right after find_child_reaper() when father->children is empty,
there is nothing to reparent in this case.
In particular this avoids find_alive_thread() and this can help if the
whole process exits and it has a lot of PF_EXITING threads at the start of
the thread list, this can easily lead to O(nr_threads ** 2) iterations.
Trivial test case (tested under KVM, 2 CPUs):
static void *tfunc(void *arg)
{
pause();
return NULL;
}
static int child(unsigned int nt)
{
pthread_t pt;
while (nt--)
assert(pthread_create(&pt, NULL, tfunc, NULL) == 0);
pthread_kill(pt, SIGTRAP);
pause();
return 0;
}
int main(int argc, const char *argv[])
{
int stat;
unsigned int nf = atoi(argv[1]);
unsigned int nt = atoi(argv[2]);
while (nf--) {
if (!fork())
return child(nt);
wait(&stat);
assert(stat == SIGTRAP);
}
return 0;
}
$ time ./test 16 16536 shows:
real user sys
- 5m37.628s 0m4.437s 8m5.560s
+ 0m50.032s 0m7.130s 1m4.927s
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Sterling Alexander <stalexan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed