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

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Message-Id: <20250423145912.3e0062864b6969b3623c8ff6@linux-foundation.org>
Date: Wed, 23 Apr 2025 14:59:12 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Huan Yang <link@...o.com>
Cc: 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>,
 cgroups@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 opensource.kernel@...o.com
Subject: Re: [PATCH 1/2] mm/memcg: use kmem_cache when alloc memcg

On Wed, 23 Apr 2025 16:43:04 +0800 Huan Yang <link@...o.com> wrote:

> @@ -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);

Why are we testing for memcg_cachep=NULL?

> @@ -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);

If it's because this allocation might have failed then let's not
bother.  If an __init-time allocation failed, this kernel is unusable
anyway.