The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), Actually the threshold
can be as big as MEMCG_CHARGE_BATCH * PAGE_SIZE. It still fits into s32.
So introducing struct batched_lruvec_stat to optimize memory usage.
The size of struct lruvec_stat is 304 bytes on 64 bits system. As it
is a per-cpu structure. So with this patch, we can save 304 / 2 * ncpu
bytes per-memcg per-node where ncpu is the number of the possible CPU.
If there are c memory cgroup (include dying cgroup) and n NUMA node in
the system. Finally, we can save (152 * ncpu * c * n) bytes.
Signed-off-by: Muchun Song <songmuc...@bytedance.com>
Reviewed-by: Shakeel Butt <shake...@google.com>
---
Changes in v2 -> v3:
- Rename per_cpu_lruvec_stat to batched_lruvec_stat. Thanks Shakeel.
- Update commit log. Thanks Roman.
Changes in v1 -> v2:
- Update the commit log to point out how many bytes that we can save.
include/linux/memcontrol.h | 14 ++++++++++++--
mm/memcontrol.c | 10 +++++++++-
2 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3febf64d1b80..076512e1dc9c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -92,6 +92,10 @@ struct lruvec_stat {
long count[NR_VM_NODE_STAT_ITEMS];
};
+struct batched_lruvec_stat {
+ s32 count[NR_VM_NODE_STAT_ITEMS];
+};
+
/*
* Bitmap of shrinker::id corresponding to memcg-aware shrinkers,
* which have elements charged to this memcg.
@@ -107,11 +111,17 @@ struct memcg_shrinker_map {
struct mem_cgroup_per_node {
struct lruvec lruvec;
- /* Legacy local VM stats */
+ /*
+ * Legacy local VM stats. This should be struct lruvec_stat and
+ * cannot be optimized to struct batched_lruvec_stat. Becasue
+ * the threshold of the lruvec_stat_cpu can be as big as
+ * MEMCG_CHARGE_BATCH * PAGE_SIZE. It can fit into s32. But this
+ * filed has no upper limit.
+ */
struct lruvec_stat __percpu *lruvec_stat_local;
/* Subtree VM stats (batched updates) */
- struct lruvec_stat __percpu *lruvec_stat_cpu;
+ struct batched_lruvec_stat __percpu *lruvec_stat_cpu;
atomic_long_t lruvec_stat[NR_VM_NODE_STAT_ITEMS];
unsigned long lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eec44918d373..1b01771f2600 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5198,7 +5198,7 @@ static int alloc_mem_cgroup_per_node_info(struct
mem_cgroup *memcg, int node)
return 1;
}
- pn->lruvec_stat_cpu = alloc_percpu_gfp(struct lruvec_stat,
+ pn->lruvec_stat_cpu = alloc_percpu_gfp(struct batched_lruvec_stat,
GFP_KERNEL_ACCOUNT);
if (!pn->lruvec_stat_cpu) {
free_percpu(pn->lruvec_stat_local);
@@ -7089,6 +7089,14 @@ static int __init mem_cgroup_init(void)
{
int cpu, node;
+ /*
+ * Currently s32 type (can refer to struct batched_lruvec_stat) is
+ * used for per-memcg-per-cpu caching of per-node statistics. In order
+ * to work fine, we should make sure that the overfill threshold can't
+ * exceed S32_MAX / PAGE_SIZE.
+ */
+ BUILD_BUG_ON(MEMCG_CHARGE_BATCH > S32_MAX / PAGE_SIZE);
+
cpuhp_setup_state_nocalls(CPUHP_MM_MEMCQ_DEAD, "mm/memctrl:dead", NULL,
memcg_hotplug_cpu_dead);
--
2.11.0
