linux-kernel - [PATCH 1/2] mm/memcg: use kmem

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Message-ID: <20250423084306.65706-2-link@vivo.com>
Date: Wed, 23 Apr 2025 16:43:04 +0800
From: Huan Yang <link@...o.com>
To: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: opensource.kernel@...o.com,
	Huan Yang <link@...o.com>
Subject: [PATCH 1/2] mm/memcg: use kmem_cache when alloc memcg

When trace mem_cgroup_alloc using trace_kmalloc, may get this output:

kmalloc: call_site=mem_cgroup_css_alloc+0xd8/0x5b4 ptr=000000003e4c3799
bytes_req=2312 bytes_alloc=4096 gfp_flags=GFP_KERNEL|__GFP_ZERO node=-1
accounted=false

If multi NUMA node, maybe above a little than 2312(8bytes * nr_node_ids).

Which mean each mem_cgroup struct only need 2312bytes but kmalloc give
4096, due to we only have kmalloc-2k and kmalloc-4k, so fallback into
kmalloc-4k. This is waste a little.

This patch use kmem_cache_alloc to alloc mem_cgroup struct. Ftrace show
like this:

kmem_cache_alloc: call_site=mem_cgroup_css_alloc+0xbc/0x5d4
ptr=00000000695c1806 bytes_req=2312 bytes_alloc=2368
gfp_flags=GFP_KERNEL|__GFP_ZERO node=-1 accounted=false

Compare to 1 memcg waste 1784bytes, this only 'waste' 56bytes due to hw
cacheline align.

Signed-off-by: Huan Yang <link@...o.com>
---
 mm/memcontrol.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5e2ea8b8a898..cb32a498e5ae 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -95,6 +95,8 @@ static bool cgroup_memory_nokmem __ro_after_init;
 /* BPF memory accounting disabled? */
 static bool cgroup_memory_nobpf __ro_after_init;
 
+static struct kmem_cache *memcg_cachep;
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 static DECLARE_WAIT_QUEUE_HEAD(memcg_cgwb_frn_waitq);
 #endif
@@ -3652,7 +3654,10 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
 	int __maybe_unused i;
 	long error;
 
-	memcg = kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL);
+	memcg = likely(memcg_cachep) ?
+			kmem_cache_zalloc(memcg_cachep, GFP_KERNEL) :
+			kzalloc(struct_size(memcg, nodeinfo, nr_node_ids),
+				GFP_KERNEL);
 	if (!memcg)
 		return ERR_PTR(-ENOMEM);
 
@@ -5039,6 +5044,7 @@ __setup("cgroup.memory=", cgroup_memory);
 static int __init mem_cgroup_init(void)
 {
 	int cpu;
+	unsigned int memcg_size;
 
 	/*
 	 * Currently s32 type (can refer to struct batched_lruvec_stat) is
@@ -5055,6 +5061,10 @@ static int __init mem_cgroup_init(void)
 		INIT_WORK(&per_cpu_ptr(&memcg_stock, cpu)->work,
 			  drain_local_stock);
 
+	memcg_size = struct_size_t(struct mem_cgroup, nodeinfo, nr_node_ids);
+	memcg_cachep = kmem_cache_create("mem_cgroup", memcg_size, 0,
+					 SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);
+
 	return 0;
 }
 subsys_initcall(mem_cgroup_init);
-- 
2.48.1