Re: [PATCH] cgroup: provide a macro helper to iterate a cgroup's ancestors

From: Zefan Li
Date: Thu Jun 27 2019 - 06:47:23 EST


On 2019/6/27 18:19, Peng Wang wrot:
Use for_each_ancestor macro to iterate a cgroup's ancestors for clarity.>

This patch doesn't make much sense to me. Because it does not reduce lines of code,
and I don't think it will reduce the size of the kernel, and the original code is
not bad in readability.

Signed-off-by: Peng Wang <rocking@xxxxxxxxxx>
---
include/linux/cgroup.h | 11 +++++++++++
kernel/cgroup/cgroup.c | 7 +++----
kernel/cgroup/freezer.c | 2 +-
kernel/cgroup/rstat.c | 4 ++--
4 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 0297f930a56e..00b0a16bbc30 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -298,6 +298,17 @@ void css_task_iter_end(struct css_task_iter *it);
; \
else
+/**
+ * for_each_ancestor - iterate a cgroup's ancestors
+ * @tcgrp: the loop cursor
+ * @cgrp: cgroup whose ancestors to iterate
+ *
+ * Iterate ancestors of @cgrp.
+ */
+#define for_each_ancestor(tcgrp, cgrp) \
+ for ((tcgrp) = cgroup_parent((cgrp)); (tcgrp); \
+ (tcgrp) = cgroup_parent((tcgrp)))
+
/*
* Inline functions.
*/
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index bf9dbffd46b1..32fa09679209 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -404,7 +404,7 @@ static bool cgroup_is_valid_domain(struct cgroup *cgrp)
return false;
/* but the ancestors can't be unless mixable */
- while ((cgrp = cgroup_parent(cgrp))) {
+ for_each_ancestor(cgrp, cgrp) {
if (!cgroup_is_mixable(cgrp) && cgroup_is_thread_root(cgrp))
return false;
if (cgroup_is_threaded(cgrp))
@@ -4987,8 +4987,7 @@ static void css_release_work_fn(struct work_struct *work)
cgroup_rstat_flush(cgrp);
spin_lock_irq(&css_set_lock);
- for (tcgrp = cgroup_parent(cgrp); tcgrp;
- tcgrp = cgroup_parent(tcgrp))
+ for_each_ancestor(tcgrp, cgrp)
tcgrp->nr_dying_descendants--;
spin_unlock_irq(&css_set_lock);
@@ -5518,7 +5517,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
parent->nr_threaded_children--;
spin_lock_irq(&css_set_lock);
- for (tcgrp = cgroup_parent(cgrp); tcgrp; tcgrp = cgroup_parent(tcgrp)) {
+ for_each_ancestor(tcgrp, cgrp) {
tcgrp->nr_descendants--;
tcgrp->nr_dying_descendants++;
/*
diff --git a/kernel/cgroup/freezer.c b/kernel/cgroup/freezer.c
index 8cf010680678..4dfc2f04a82d 100644
--- a/kernel/cgroup/freezer.c
+++ b/kernel/cgroup/freezer.c
@@ -21,7 +21,7 @@ static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
*
* Otherwise, all ancestor cgroups are forced into the non-frozen state.
*/
- while ((cgrp = cgroup_parent(cgrp))) {
+ for_each_ancestor(cgrp, cgrp) {
if (frozen) {
cgrp->freezer.nr_frozen_descendants += desc;
if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index ca19b4c8acf5..58d352e0d76a 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -49,8 +49,7 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
raw_spin_lock_irqsave(cpu_lock, flags);
/* put @cgrp and all ancestors on the corresponding updated lists */
- for (parent = cgroup_parent(cgrp); parent;
- cgrp = parent, parent = cgroup_parent(cgrp)) {
+ for_each_ancestor(parent, cgrp) {
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu);
@@ -63,6 +62,7 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
rstatc->updated_next = prstatc->updated_children;
prstatc->updated_children = cgrp;
+ cgrp = parent;
}
raw_spin_unlock_irqrestore(cpu_lock, flags);