[PATCH 2/6] memcg: split mem_cgroup_private_id into two fields

[Shakeel Butt <shakeel.butt@linux.dev>]

The two members of struct mem_cgroup_private_id have different access
patterns. The id is read on every eviction and refault through
mem_cgroup_private_id(), and is only written when the memcg is created
and destroyed. The ref is written on every swap charge and uncharge.

Split them into private_id and private_id_ref so a later patch can put
them into different cache line groups. A struct member cannot be split
across two groups.

No functional change.

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 include/linux/memcontrol.h | 10 +++-------
 mm/memcontrol.c            | 18 +++++++++---------
 2 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ac575fcc5f1e..46fc99786ebd 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -66,11 +66,6 @@ struct mem_cgroup_reclaim_cookie {
 
 #define MEM_CGROUP_ID_SHIFT	16
 
-struct mem_cgroup_private_id {
-	int id;
-	refcount_t ref;
-};
-
 struct memcg_vmstats_percpu;
 struct memcg1_events_percpu;
 struct memcg_vmstats;
@@ -189,7 +184,8 @@ struct mem_cgroup {
 	struct cgroup_subsys_state css;
 
 	/* Private memcg ID. Used to ID objects that outlive the cgroup */
-	struct mem_cgroup_private_id id;
+	int private_id;
+	refcount_t private_id_ref;
 
 	/* Accounted resources */
 	struct page_counter memory;		/* Both v1 & v2 */
@@ -811,7 +807,7 @@ static inline unsigned short mem_cgroup_private_id(struct mem_cgroup *memcg)
 	if (mem_cgroup_disabled())
 		return 0;
 
-	return memcg->id.id;
+	return memcg->private_id;
 }
 struct mem_cgroup *mem_cgroup_from_private_id(unsigned short id);
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9a65d7148c22..c42297ae3b0e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3797,7 +3797,7 @@ static void memcg_online_kmem(struct mem_cgroup *memcg)
 
 	static_branch_enable(&memcg_kmem_online_key);
 
-	memcg->kmemcg_id = memcg->id.id;
+	memcg->kmemcg_id = memcg->private_id;
 }
 
 static void memcg_offline_kmem(struct mem_cgroup *memcg)
@@ -4056,15 +4056,15 @@ static DEFINE_XARRAY_ALLOC1(mem_cgroup_private_ids);
 
 static void mem_cgroup_private_id_remove(struct mem_cgroup *memcg)
 {
-	if (memcg->id.id > 0) {
-		xa_erase(&mem_cgroup_private_ids, memcg->id.id);
-		memcg->id.id = 0;
+	if (memcg->private_id > 0) {
+		xa_erase(&mem_cgroup_private_ids, memcg->private_id);
+		memcg->private_id = 0;
 	}
 }
 
 static inline void mem_cgroup_private_id_put(struct mem_cgroup *memcg, unsigned int n)
 {
-	if (refcount_sub_and_test(n, &memcg->id.ref)) {
+	if (refcount_sub_and_test(n, &memcg->private_id_ref)) {
 		mem_cgroup_private_id_remove(memcg);
 
 		/* Memcg ID pins CSS */
@@ -4074,7 +4074,7 @@ static inline void mem_cgroup_private_id_put(struct mem_cgroup *memcg, unsigned
 
 struct mem_cgroup *mem_cgroup_private_id_get_online(struct mem_cgroup *memcg, unsigned int n)
 {
-	while (!refcount_add_not_zero(n, &memcg->id.ref)) {
+	while (!refcount_add_not_zero(n, &memcg->private_id_ref)) {
 		/*
 		 * The root cgroup cannot be destroyed, so it's refcount must
 		 * always be >= 1.
@@ -4198,7 +4198,7 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
 	if (!memcg)
 		return ERR_PTR(-ENOMEM);
 
-	error = xa_alloc(&mem_cgroup_private_ids, &memcg->id.id, NULL,
+	error = xa_alloc(&mem_cgroup_private_ids, &memcg->private_id, NULL,
 			 XA_LIMIT(1, MEM_CGROUP_ID_MAX), GFP_KERNEL);
 	if (error)
 		goto fail;
@@ -4345,7 +4345,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	lru_gen_online_memcg(memcg);
 
 	/* Online state pins memcg ID, memcg ID pins CSS */
-	refcount_set(&memcg->id.ref, 1);
+	refcount_set(&memcg->private_id_ref, 1);
 	css_get(css);
 
 	/*
@@ -4358,7 +4358,7 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 	 * publish it here at the end of onlining. This matches the
 	 * regular ID destruction during offlining.
 	 */
-	xa_store(&mem_cgroup_private_ids, memcg->id.id, memcg, GFP_KERNEL);
+	xa_store(&mem_cgroup_private_ids, memcg->private_id, memcg, GFP_KERNEL);
 
 	return 0;
 free_objcg:
-- 
2.53.0-Meta