[PATCH 2/2] mm/memcg: use kmem_cache when alloc memcg pernode info

[Huan Yang <link@vivo.com>]

When trace mem_cgroup_alloc using trace_kmalloc, may get this output:

kmalloc: call_site=mem_cgroup_css_alloc+0x1d8/0x5b4 ptr=00000000d798700c
bytes_req=2896 bytes_alloc=4096 gfp_flags=GFP_KERNEL|__GFP_ZERO node=0
accounted=false

Due to each memcg will alloc per_nodeinfo for each NUMA node, and each
NUMA node is 2896bytes but kmalloc also given 4096bytes, that mean 1
memcg on each NUMA node will waste 1200bytes.

This patch use kmem_cache when alloc mem_cgroup_per_nodeinfo for each
NUMA node. By this, ftrace how like:

kmem_cache_alloc: call_site=mem_cgroup_css_alloc+0x1b8/0x5d4
ptr=000000002989e63a bytes_req=2896 bytes_alloc=2944
gfp_flags=GFP_KERNEL|__GFP_ZERO node=0 accounted=false

Compare to kmalloc, this only "waste" 48bytes per node due to HW
cacheline align

Signed-off-by: Huan Yang <link@vivo.com>
---
 mm/memcontrol.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cb32a498e5ae..e8797382aeb4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -96,6 +96,7 @@ static bool cgroup_memory_nokmem __ro_after_init;
 static bool cgroup_memory_nobpf __ro_after_init;
 
 static struct kmem_cache *memcg_cachep;
+static struct kmem_cache *memcg_pn_cachep;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 static DECLARE_WAIT_QUEUE_HEAD(memcg_cgwb_frn_waitq);
@@ -3601,7 +3602,10 @@ static bool alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn;
 
-	pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, node);
+	pn = likely(memcg_pn_cachep) ?
+		     kmem_cache_alloc_node(memcg_pn_cachep,
+					   GFP_KERNEL | __GFP_ZERO, node) :
+		     kzalloc_node(sizeof(*pn), GFP_KERNEL, node);
 	if (!pn)
 		return false;
 
@@ -5065,6 +5069,9 @@ static int __init mem_cgroup_init(void)
 	memcg_cachep = kmem_cache_create("mem_cgroup", memcg_size, 0,
 					 SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);
 
+	memcg_pn_cachep = KMEM_CACHE(mem_cgroup_per_node,
+				     SLAB_PANIC | SLAB_HWCACHE_ALIGN);
+
 	return 0;
 }
 subsys_initcall(mem_cgroup_init);
-- 
2.48.1