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Message-ID: <20240905134130.1176443-3-chenridong@huawei.com>
Date: Thu, 5 Sep 2024 13:41:29 +0000
From: Chen Ridong <chenridong@...wei.com>
To: <tj@...nel.org>, <lizefan.x@...edance.com>, <hannes@...xchg.org>,
<longman@...hat.com>, <adityakali@...gle.com>, <sergeh@...nel.org>,
<mkoutny@...e.com>
CC: <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<chenridong@...weicloud.com>
Subject: [PATCH v1 -next 2/3] cgroup/freezer: Reduce redundant propagation for cgroup_propagate_frozen
When a cgroup is frozen/unfrozen, it will always propagate down to up.
However it is unnecessary to propagate to the top every time. This patch
aims to reduce redundant propagation for cgroup_propagate_frozen.
For example, subtree like:
a
|
b
/ | \
c d e
If c is frozen, and d and e are not frozen now, it doesn't have to
propagate to a; Only when c, d and e are all frozen, b and a could be set
to frozen. Therefore, if nr_frozen_descendants is not equal to
nr_descendants, just stop propagate. If a descendant is frozen, the
parent's nr_frozen_descendants add child->nr_descendants + 1. This can
reduce redundant propagation.
Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
kernel/cgroup/freezer.c | 31 +++++++++++++++++++++++--------
1 file changed, 23 insertions(+), 8 deletions(-)
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index 02af6c1fa957..e4bcc41b6a30 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -13,7 +13,7 @@
*/
static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
{
- int desc = 1;
+ struct cgroup *child = cgrp;
/*
* If the new state is frozen, some freezing ancestor cgroups may change
@@ -23,23 +23,38 @@ static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
*/
while ((cgrp = cgroup_parent(cgrp))) {
if (frozen) {
- cgrp->freezer.nr_frozen_descendants += desc;
+ /*
+ * A cgroup is frozen, parent nr frozen descendants should add
+ * nr cgroups of the entire subtree , including child itself.
+ */
+ cgrp->freezer.nr_frozen_descendants += child->nr_descendants + 1;
+
+ /*
+ * If there is other descendant is not frozen,
+ * cgrp and its parent couldn't be frozen, just break
+ */
+ if (cgrp->freezer.nr_frozen_descendants !=
+ cgrp->nr_descendants)
+ break;
+
+ child = cgrp;
if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
- test_bit(CGRP_FREEZE, &cgrp->flags) &&
- cgrp->freezer.nr_frozen_descendants ==
- cgrp->nr_descendants) {
+ test_bit(CGRP_FREEZE, &cgrp->flags)) {
set_bit(CGRP_FROZEN, &cgrp->flags);
cgroup_file_notify(&cgrp->events_file);
TRACE_CGROUP_PATH(notify_frozen, cgrp, 1);
- desc++;
}
} else {
- cgrp->freezer.nr_frozen_descendants -= desc;
+ cgrp->freezer.nr_frozen_descendants -= (child->nr_descendants + 1);
+
+ child = cgrp;
if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
clear_bit(CGRP_FROZEN, &cgrp->flags);
cgroup_file_notify(&cgrp->events_file);
TRACE_CGROUP_PATH(notify_frozen, cgrp, 0);
- desc++;
+ } else {
+ /* If parent is unfrozen, don't have to propagate more */
+ break;
}
}
}
--
2.34.1
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