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authorOleg Nesterov <oleg@redhat.com>2009-12-17 18:27:15 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-17 18:45:31 -0500
commit9cd80bbb07fcd6d4d037fad4297496d3b132ac6b (patch)
tree322216d34b6d5ba2366f53ba0d677950c4cde766 /kernel/fork.c
parent0f67b0b0392ccca98459bf40b36c0037793b5f71 (diff)
do_wait() optimization: do not place sub-threads on task_struct->children list
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@redhat.com> Cc: Roland McGrath <roland@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Ratan Nalumasu <rnalumasu@gmail.com> Cc: Vitaly Mayatskikh <vmayatsk@redhat.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 202a0ba63d3c..5b2959b3ffc2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1291,7 +1291,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
1291 } 1291 }
1292 1292
1293 if (likely(p->pid)) { 1293 if (likely(p->pid)) {
1294 list_add_tail(&p->sibling, &p->real_parent->children);
1295 tracehook_finish_clone(p, clone_flags, trace); 1294 tracehook_finish_clone(p, clone_flags, trace);
1296 1295
1297 if (thread_group_leader(p)) { 1296 if (thread_group_leader(p)) {
@@ -1303,6 +1302,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
1303 p->signal->tty = tty_kref_get(current->signal->tty); 1302 p->signal->tty = tty_kref_get(current->signal->tty);
1304 attach_pid(p, PIDTYPE_PGID, task_pgrp(current)); 1303 attach_pid(p, PIDTYPE_PGID, task_pgrp(current));
1305 attach_pid(p, PIDTYPE_SID, task_session(current)); 1304 attach_pid(p, PIDTYPE_SID, task_session(current));
1305 list_add_tail(&p->sibling, &p->real_parent->children);
1306 list_add_tail_rcu(&p->tasks, &init_task.tasks); 1306 list_add_tail_rcu(&p->tasks, &init_task.tasks);
1307 __get_cpu_var(process_counts)++; 1307 __get_cpu_var(process_counts)++;
1308 } 1308 }