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charset="utf-8" When tracing mem_cgroup_alloc() with kmalloc ftrace, we observe: kmalloc: call_site=3Dmem_cgroup_css_alloc+0xd8/0x5b4 ptr=3D000000003e4c3799 bytes_req=3D2312 bytes_alloc=3D4096 gfp_flags=3DGFP_KERNEL|__GFP_ZERO n= ode=3D-1 accounted=3Dfalse The output indicates that while allocating mem_cgroup struct (2312 bytes), the slab allocator actually provides 4KB chunks. This occurs because: 1. The slab allocator predefines bucket sizes from 64B to 8096B 2. The mem_cgroup allocation size (2312 bytes) falls between the 2KB and 4KB slabs 3. The allocator rounds up to the nearest larger slab (4KB), resulting in ~1KB wasted memory per allocation This patch introduces a dedicated kmem_cache for mem_cgroup structs, achieving precise memory allocation. Post-patch ftrace verification shows: kmem_cache_alloc: call_site=3Dmem_cgroup_css_alloc+0xbc/0x5d4 ptr=3D00000000695c1806 bytes_req=3D2312 bytes_alloc=3D2368 gfp_flags=3DGFP_KERNEL|__GFP_ZERO node=3D-1 accounted=3Dfalse Each memcg alloc offer 2368 bytes(include hw cacheline align), compare to 4KB, avoid waste. Signed-off-by: Huan Yang --- 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 me= m_cgroup *parent) int __maybe_unused i; long error; - memcg =3D kzalloc(struct_size(memcg, nodeinfo, nr_node_ids), GFP_KERNEL); + memcg =3D 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=3D", 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 =3D struct_size_t(struct mem_cgroup, nodeinfo, nr_node_ids); + memcg_cachep =3D kmem_cache_create("mem_cgroup", memcg_size, 0, + SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL); + return 0; } subsys_initcall(mem_cgroup_init); -- 2.48.1