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authorOleg Nesterov <oleg@redhat.com>2014-12-10 15:55:17 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-10 17:41:18 -0800
commitad9e206aefa56788b676ebcd6329e828f40d2238 (patch)
tree860bf8397db9bab9bbf96f5d5f37c522f77a1f22 /kernel/exit.c
parentc9dc05bfdb3f7fd7c00f3cbd33816c99d2cb9029 (diff)
downloadlinux-sh-ad9e206aefa56788b676ebcd6329e828f40d2238.tar.gz
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>
Diffstat (limited to 'kernel/exit.c')
-rw-r--r--kernel/exit.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index b0f482f5daf9..063745699f7f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -571,6 +571,8 @@ static void forget_original_parent(struct task_struct *father)
/* Can drop and reacquire tasklist_lock */
reaper = find_child_reaper(father);
+ if (list_empty(&father->children))
+ goto unlock;
reaper = find_new_reaper(father, reaper);
list_for_each_entry(p, &father->children, sibling) {
@@ -591,6 +593,7 @@ static void forget_original_parent(struct task_struct *father)
reparent_leader(father, p, &dead_children);
}
list_splice_tail_init(&father->children, &reaper->children);
+ unlock:
write_unlock_irq(&tasklist_lock);
list_for_each_entry_safe(p, n, &dead_children, ptrace_entry) {