[PATCH 4/4 v2] cgroup: separate rstat list pointers from base stats

inwardvessel
2025-02-27T21:56:02Z

From: JP Kobryn <inwardvessel@gmail.com>

A majority of the cgroup_rstat_cpu struct size is made up of the base
stat entities. Since only the "self" subsystem state makes use of these,
move them into a struct of their own. This allows for a new compact
cgroup_rstat_cpu struct that the formal subsystems can make use of.
Where applicable, decide on whether to allocate the compact or full
struct including the base stats.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
---
include/linux/cgroup-defs.h | 37 ++++++++++++++----------
kernel/cgroup/rstat.c | 57 +++++++++++++++++++++++++------------
2 files changed, 61 insertions(+), 33 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 1598e1389615..b0a07c63fd46 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -170,7 +170,10 @@ struct cgroup_subsys_state {
struct percpu_ref refcnt;

/* per-cpu recursive resource statistics */
- struct cgroup_rstat_cpu __percpu *rstat_cpu;
+ union {
+ struct cgroup_rstat_cpu __percpu *rstat_cpu;
+ struct cgroup_rstat_base_cpu __percpu *rstat_base_cpu;
+ };

/*
* siblings list anchored at the parent's ->children
@@ -356,6 +359,24 @@ struct cgroup_base_stat {
* resource statistics on top of it - bsync, bstat and last_bstat.
*/
struct cgroup_rstat_cpu {
+ /*
+ * Child cgroups with stat updates on this cpu since the last read
+ * are linked on the parent's ->updated_children through
+ * ->updated_next.
+ *
+ * In addition to being more compact, singly-linked list pointing
+ * to the cgroup makes it unnecessary for each per-cpu struct to
+ * point back to the associated cgroup.
+ *
+ * Protected by per-cpu cgroup_rstat_cpu_lock.
+ */
+ struct cgroup_subsys_state *updated_children; /* terminated by self */
+ struct cgroup_subsys_state *updated_next; /* NULL if not on list */
+};
+
+struct cgroup_rstat_base_cpu {
+ struct cgroup_rstat_cpu self;
+
/*
* ->bsync protects ->bstat. These are the only fields which get
* updated in the hot path.
@@ -382,20 +403,6 @@ struct cgroup_rstat_cpu {
* deltas to propagate to the per-cpu subtree_bstat.
*/
struct cgroup_base_stat last_subtree_bstat;
-
- /*
- * Child cgroups with stat updates on this cpu since the last read
- * are linked on the parent's ->updated_children through
- * ->updated_next.
- *
- * In addition to being more compact, singly-linked list pointing
- * to the cgroup makes it unnecessary for each per-cpu struct to
- * point back to the associated cgroup.
- *
- * Protected by per-cpu cgroup_rstat_cpu_lock.
- */
- struct cgroup_subsys_state *updated_children; /* terminated by self */
- struct cgroup_subsys_state *updated_next; /* NULL if not on list */
};

struct cgroup_freezer_state {
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index b3eaefc1fd07..c08ebe2f9568 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -24,6 +24,12 @@ static struct cgroup_rstat_cpu *cgroup_rstat_cpu(
return per_cpu_ptr(css->rstat_cpu, cpu);
}

+static struct cgroup_rstat_base_cpu *cgroup_rstat_base_cpu(
+ struct cgroup_subsys_state *css, int cpu)
+{
+ return per_cpu_ptr(css->rstat_base_cpu, cpu);
+}
+
static inline bool is_base_css(struct cgroup_subsys_state *css)
{
return css->ss == NULL;
@@ -438,17 +444,31 @@ int cgroup_rstat_init(struct cgroup_subsys_state *css)

/* the root cgrp's self css has rstat_cpu preallocated */
if (!css->rstat_cpu) {
- css->rstat_cpu = alloc_percpu(struct cgroup_rstat_cpu);
- if (!css->rstat_cpu)
- return -ENOMEM;
- }
+ if (is_base_css(css)) {
+ css->rstat_base_cpu = alloc_percpu(struct cgroup_rstat_base_cpu);
+ if (!css->rstat_base_cpu)
+ return -ENOMEM;

- /* ->updated_children list is self terminated */
- for_each_possible_cpu(cpu) {
- struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(css, cpu);
+ for_each_possible_cpu(cpu) {
+ struct cgroup_rstat_base_cpu *rstatc;
+
+ rstatc = cgroup_rstat_base_cpu(css, cpu);
+ rstatc->self.updated_children = css;
+ u64_stats_init(&rstatc->bsync);
+ }
+ } else {
+ css->rstat_cpu = alloc_percpu(struct cgroup_rstat_cpu);
+ if (!css->rstat_cpu)
+ return -ENOMEM;
+
+ for_each_possible_cpu(cpu) {
+ struct cgroup_rstat_cpu *rstatc;
+
+ rstatc = cgroup_rstat_cpu(css, cpu);
+ rstatc->updated_children = css;
+ }
+ }

- rstatc->updated_children = css;
- u64_stats_init(&rstatc->bsync);
}

return 0;
@@ -522,9 +542,10 @@ static void cgroup_base_stat_sub(struct cgroup_base_stat *dst_bstat,

static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
{
- struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(&cgrp->self, cpu);
+ struct cgroup_rstat_base_cpu *rstatc = cgroup_rstat_base_cpu(
+ &cgrp->self, cpu);
struct cgroup *parent = cgroup_parent(cgrp);
- struct cgroup_rstat_cpu *prstatc;
+ struct cgroup_rstat_base_cpu *prstatc;
struct cgroup_base_stat delta;
unsigned seq;

@@ -552,25 +573,25 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
cgroup_base_stat_add(&cgrp->last_bstat, &delta);

delta = rstatc->subtree_bstat;
- prstatc = cgroup_rstat_cpu(&parent->self, cpu);
+ prstatc = cgroup_rstat_base_cpu(&parent->self, cpu);
cgroup_base_stat_sub(&delta, &rstatc->last_subtree_bstat);
cgroup_base_stat_add(&prstatc->subtree_bstat, &delta);
cgroup_base_stat_add(&rstatc->last_subtree_bstat, &delta);
}
}

-static struct cgroup_rstat_cpu *
+static struct cgroup_rstat_base_cpu *
cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp, unsigned long *flags)
{
- struct cgroup_rstat_cpu *rstatc;
+ struct cgroup_rstat_base_cpu *rstatc;

- rstatc = get_cpu_ptr(cgrp->self.rstat_cpu);
+ rstatc = get_cpu_ptr(cgrp->self.rstat_base_cpu);
*flags = u64_stats_update_begin_irqsave(&rstatc->bsync);
return rstatc;
}

static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
- struct cgroup_rstat_cpu *rstatc,
+ struct cgroup_rstat_base_cpu *rstatc,
unsigned long flags)
{
u64_stats_update_end_irqrestore(&rstatc->bsync, flags);
@@ -580,7 +601,7 @@ static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,

void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
{
- struct cgroup_rstat_cpu *rstatc;
+ struct cgroup_rstat_base_cpu *rstatc;
unsigned long flags;

rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);
@@ -591,7 +612,7 @@ void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
void __cgroup_account_cputime_field(struct cgroup *cgrp,
enum cpu_usage_stat index, u64 delta_exec)
{
- struct cgroup_rstat_cpu *rstatc;
+ struct cgroup_rstat_base_cpu *rstatc;
unsigned long flags;

rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);
--
2.43.5