The patch titled
Subject: exit: reparent: avoid find_new_reaper() if no children
has been added to the -mm tree. Its filename is
exit-reparent-avoid-find_new_reaper-if-no-children.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/exit-reparent-avoid-find_new_reaper-if-no-children.patch
echo and later at
echo http://ozlabs.org/~akpm/mmotm/broken-out/exit-reparent-avoid-find_new_reaper-if-no-children.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Sterling Alexander <stalexan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN kernel/exit.c~exit-reparent-avoid-find_new_reaper-if-no-children kernel/exit.c
--- a/kernel/exit.c~exit-reparent-avoid-find_new_reaper-if-no-children
+++ a/kernel/exit.c
@@ -571,6 +571,8 @@ static void forget_original_parent(struc
/* 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(struc
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) {
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
mmfs-introduce-helpers-around-the-i_mmap_mutex.patch
mm-use-new-helper-functions-around-the-i_mmap_mutex.patch
mm-convert-i_mmap_mutex-to-rwsem.patch
mm-rmap-share-the-i_mmap_rwsem.patch
uprobes-share-the-i_mmap_rwsem.patch
mm-xip-share-the-i_mmap_rwsem.patch
mm-memory-failure-share-the-i_mmap_rwsem.patch
mm-nommu-share-the-i_mmap_rwsem.patch
mm-memoryc-share-the-i_mmap_rwsem.patch
remove-unnecessary-is_valid_nodemask.patch
proc-task_state-read-cred-group_info-outside-of-task_lock.patch
proc-task_state-deuglify-the-max_fds-calculation.patch
proc-task_state-move-the-main-seq_printf-outside-of-rcu_read_lock.patch
proc-task_state-ptrace_parent-doesnt-need-pid_alive-check.patch
sched_show_task-fix-unsafe-usage-of-real_parent.patch
exit-reparent-use-ptrace_entry-rather-than-sibling-for-exit_dead-tasks.patch
exit-reparent-cleanup-the-changing-of-parent.patch
exit-reparent-cleanup-the-changing-of-parent-fix.patch
exit-reparent-cleanup-the-usage-of-reparent_leader.patch
exit-ptrace-shift-reap-dead-code-from-exit_ptrace-to-forget_original_parent.patch
usermodehelper-dont-use-clone_vfork-for-____call_usermodehelper.patch
usermodehelper-kill-the-kmod_thread_locker-logic.patch
exit-wait-cleanup-the-ptrace_reparented-checks.patch
exit-wait-cleanup-the-ptrace_reparented-checks-fix.patch
exit-wait-dont-use-zombie-real_parent.patch
exit-wait-drop-tasklist_lock-before-psig-c-accounting.patch
exit-release_task-fix-the-comment-about-group-leader-accounting.patch
exit-proc-dont-try-to-flush-proc-tgid-task-tgid.patch
exit-reparent-fix-the-dead-parent-pr_set_child_subreaper-reparenting.patch
exit-reparent-fix-the-cross-namespace-pr_set_child_subreaper-reparenting.patch
exit-reparent-s-while_each_thread-for_each_thread-in-find_new_reaper.patch
exit-reparent-document-the-has_child_subreaper-checks.patch
exit-reparent-introduce-find_child_reaper.patch
exit-reparent-introduce-find_alive_thread.patch
exit-reparent-avoid-find_new_reaper-if-no-children.patch
exit-reparent-call-forget_original_parent-under-tasklist_lock.patch
exit-exit_notify-re-use-dead-list-to-autoreap-current.patch
linux-next.patch
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