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

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Message-ID: <7aa9ae65-12a1-4a26-9405-216e6b00b6d6@vivo.com>
Date: Thu, 24 Apr 2025 09:46:59 +0800
From: Huan Yang <link@...o.com>
To: Andrew Morton <akpm@...ux-foundation.org>
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


在 2025/4/24 05:59, Andrew Morton 写道:
> 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?

Due to cgroup_init ahead of initcall, hence, root_mem_cgroup create will trigger NULL pointer access.

So, here test it. :)

I don't find a more good way to avoid this.

>
>> @@ -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.
>
>