The patch titled
do_wait() optimization: do not place sub-threads on task_struct->children list
has been added to the -mm tree. Its filename is
do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch
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------------------------------------------------------
Subject: do_wait() optimization: do not place sub-threads on task_struct->children list
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Thanks to Roland who pointed out de_thread() issues.
Currently we add sub-threads to ->real_parent->children list. This buys
nothing but slows down do_wait().
With this patch ->children contains only main threads (group leaders).
The only complication is that forget_original_parent() should iterate over
sub-threads by hand, and de_thread() needs another list_replace() when it
changes ->group_leader.
Henceforth do_wait_thread() can never see task_detached() && !EXIT_DEAD
tasks, we can remove this check (and we can unify do_wait_thread() and
ptrace_do_wait()).
This change can confuse the optimistic search in mm_update_next_owner(),
but this is fixable and minor.
Perhaps badness() and oom_kill_process() should be updated, but they
should be fixed in any case.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Ratan Nalumasu <rnalumasu@xxxxxxxxx>
Cc: Vitaly Mayatskikh <vmayatsk@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 2 ++
kernel/exit.c | 36 +++++++++++++++++-------------------
kernel/fork.c | 2 +-
3 files changed, 20 insertions(+), 20 deletions(-)
diff -puN fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list fs/exec.c
--- a/fs/exec.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/fs/exec.c
@@ -827,7 +827,9 @@ static int de_thread(struct task_struct
attach_pid(tsk, PIDTYPE_PID, task_pid(leader));
transfer_pid(leader, tsk, PIDTYPE_PGID);
transfer_pid(leader, tsk, PIDTYPE_SID);
+
list_replace_rcu(&leader->tasks, &tsk->tasks);
+ list_replace_init(&leader->sibling, &tsk->sibling);
tsk->group_leader = tsk;
leader->group_leader = tsk;
diff -puN kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/exit.c
--- a/kernel/exit.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/kernel/exit.c
@@ -68,10 +68,10 @@ static void __unhash_process(struct task
detach_pid(p, PIDTYPE_SID);
list_del_rcu(&p->tasks);
+ list_del_init(&p->sibling);
__get_cpu_var(process_counts)--;
}
list_del_rcu(&p->thread_group);
- list_del_init(&p->sibling);
}
/*
@@ -738,12 +738,9 @@ static struct task_struct *find_new_reap
/*
* Any that need to be release_task'd are put on the @dead list.
*/
-static void reparent_thread(struct task_struct *father, struct task_struct *p,
+static void reparent_leader(struct task_struct *father, struct task_struct *p,
struct list_head *dead)
{
- if (p->pdeath_signal)
- group_send_sig_info(p->pdeath_signal, SEND_SIG_NOINFO, p);
-
list_move_tail(&p->sibling, &p->real_parent->children);
if (task_detached(p))
@@ -782,12 +779,18 @@ static void forget_original_parent(struc
reaper = find_new_reaper(father);
list_for_each_entry_safe(p, n, &father->children, sibling) {
- p->real_parent = reaper;
- if (p->parent == father) {
- BUG_ON(task_ptrace(p));
- p->parent = p->real_parent;
- }
- reparent_thread(father, p, &dead_children);
+ struct task_struct *t = p;
+ do {
+ t->real_parent = reaper;
+ if (t->parent == father) {
+ BUG_ON(task_ptrace(t));
+ t->parent = t->real_parent;
+ }
+ if (t->pdeath_signal)
+ group_send_sig_info(t->pdeath_signal,
+ SEND_SIG_NOINFO, t);
+ } while_each_thread(p, t);
+ reparent_leader(father, p, &dead_children);
}
write_unlock_irq(&tasklist_lock);
@@ -1541,14 +1544,9 @@ static int do_wait_thread(struct wait_op
struct task_struct *p;
list_for_each_entry(p, &tsk->children, sibling) {
- /*
- * Do not consider detached threads.
- */
- if (!task_detached(p)) {
- int ret = wait_consider_task(wo, tsk, 0, p);
- if (ret)
- return ret;
- }
+ int ret = wait_consider_task(wo, tsk, 0, p);
+ if (ret)
+ return ret;
}
return 0;
diff -puN kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list kernel/fork.c
--- a/kernel/fork.c~do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list
+++ a/kernel/fork.c
@@ -1248,7 +1248,6 @@ static struct task_struct *copy_process(
}
if (likely(p->pid)) {
- list_add_tail(&p->sibling, &p->real_parent->children);
tracehook_finish_clone(p, clone_flags, trace);
if (thread_group_leader(p)) {
@@ -1260,6 +1259,7 @@ static struct task_struct *copy_process(
p->signal->tty = tty_kref_get(current->signal->tty);
attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
attach_pid(p, PIDTYPE_SID, task_session(current));
+ list_add_tail(&p->sibling, &p->real_parent->children);
list_add_tail_rcu(&p->tasks, &init_task.tasks);
__get_cpu_var(process_counts)++;
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
linux-next.patch
cred_guard_mutex-do-not-return-eintr-to-user-space.patch
rework-fix-is_single_threaded.patch
getrusage-fill-ru_maxrss-value.patch
getrusage-fill-ru_maxrss-value-update.patch
ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee.patch
do_wait-wakeup-optimization-shift-security_task_wait-from-eligible_child-to-wait_consider_task.patch
do_wait-wakeup-optimization-change-__wake_up_parent-to-use-filtered-wakeup.patch
do_wait-wakeup-optimization-child_wait_callback-check-__wnothread-case.patch
do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch
signals-tracehook_notify_jctl-change.patch
utrace-core.patch
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