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Subject[PATCH] cgroup: Return if dst_cgrp equals to src_cgrp
Date
In function cgroup_migrate_add_src(), if dst_cgrp
equals to src_cgroup which the tasks link, dont
go on migrating tasks to another css_set.
This can save the cost of unnecessary migration.

Signed-off-by: shisiyuan <shisiyuan@xiaomi.com>
---
kernel/cgroup/cgroup.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 6139460..97d7f68 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2634,6 +2634,9 @@ void cgroup_migrate_add_src(struct css_set *src_cset,

src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);

+ if (src_cgrp == dst_cgrp)
+ return;
+
if (!list_empty(&src_cset->mg_preload_node))
return;

@@ -2780,6 +2783,9 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
rcu_read_unlock();
spin_unlock_irq(&css_set_lock);

+ if (list_empty(&mgctx.preloaded_src_csets))
+ return ret;
+
/* prepare dst csets and commit */
ret = cgroup_migrate_prepare_dst(&mgctx);
if (!ret)
@@ -2927,7 +2933,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
struct cgroup_subsys_state *d_css;
struct cgroup *dsct;
struct css_set *src_cset;
- int ret;
+ int ret = 0;

lockdep_assert_held(&cgroup_mutex);

@@ -2943,6 +2949,9 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
}
spin_unlock_irq(&css_set_lock);

+ if (list_empty(&mgctx.preloaded_src_csets))
+ goto out_finish;
+
/* NULL dst indicates self on default hierarchy */
ret = cgroup_migrate_prepare_dst(&mgctx);
if (ret)
--
2.7.4
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