From 892a2b90ba15cb7dbee40979f23fdb492913abf8 Mon Sep 17 00:00:00 2001 From: Mandeep Singh Baines Date: Wed, 21 Dec 2011 20:18:37 -0800 Subject: [PATCH] cgroup: only need to check oldcgrp==newgrp once In cgroup_attach_proc it is now sufficient to only check that oldcgrp==newcgrp once. Now that we are using threadgroup_lock() during the migrations, oldcgrp will not change. Signed-off-by: Mandeep Singh Baines Acked-by: Li Zefan Signed-off-by: Tejun Heo Cc: containers@lists.linux-foundation.org Cc: cgroups@vger.kernel.org Cc: KAMEZAWA Hiroyuki Cc: Frederic Weisbecker Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage --- kernel/cgroup.c | 22 ++++++---------------- 1 file changed, 6 insertions(+), 16 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index a85a7002ca33..1042b3c41314 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2067,7 +2067,7 @@ static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg, */ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) { - int retval, i, group_size, nr_migrating_tasks; + int retval, i, group_size; struct cgroup_subsys *ss, *failed_ss = NULL; /* guaranteed to be initialized later, but the compiler needs this */ struct css_set *oldcg; @@ -2118,7 +2118,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) } tsk = leader; - i = nr_migrating_tasks = 0; + i = 0; do { struct task_and_cgroup ent; @@ -2134,11 +2134,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) */ ent.task = tsk; ent.cgrp = task_cgroup_from_root(tsk, root); + /* nothing to do if this task is already in the cgroup */ + if (ent.cgrp == cgrp) + continue; retval = flex_array_put(group, i, &ent, GFP_ATOMIC); BUG_ON(retval != 0); i++; - if (ent.cgrp != cgrp) - nr_migrating_tasks++; } while_each_thread(leader, tsk); /* remember the number of threads in the array for later. */ group_size = i; @@ -2148,7 +2149,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) /* methods shouldn't be called if no task is actually migrating */ retval = 0; - if (!nr_migrating_tasks) + if (!group_size) goto out_free_group_list; /* @@ -2171,14 +2172,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) INIT_LIST_HEAD(&newcg_list); for (i = 0; i < group_size; i++) { tc = flex_array_get(group, i); - /* nothing to do if this task is already in the cgroup */ - if (tc->cgrp == cgrp) - continue; - /* - * get old css_set pointer. threadgroup is locked so this is - * safe against concurrent cgroup_exit() changing this to - * init_css_set. - */ oldcg = tc->task->cgroups; /* if we don't already have it in the list get a new one */ @@ -2194,9 +2187,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) */ for (i = 0; i < group_size; i++) { tc = flex_array_get(group, i); - /* leave current thread as it is if it's already there */ - if (tc->cgrp == cgrp) - continue; retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true); BUG_ON(retval); } -- 2.20.1