linux-kernel - Re: [PATCH v3 12/28] slab: pass memcg parameter to kmem_cache

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Date:	Tue, 29 May 2012 19:50:39 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, <kamezawa.hiroyu@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, <devel@...nvz.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v3 12/28] slab: pass memcg parameter to kmem_cache_create

On 05/29/2012 06:27 PM, Christoph Lameter wrote:
> On Fri, 25 May 2012, Glauber Costa wrote:
>
>> index 06e4a3e..7c0cdd6 100644
>> --- a/include/linux/slab_def.h
>> +++ b/include/linux/slab_def.h
>> @@ -102,6 +102,13 @@ struct kmem_cache {
>>   	 */
>>   };
>>
>> +static inline void store_orig_align(struct kmem_cache *cachep, int orig_align)
>> +{
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> +	cachep->memcg_params.orig_align = orig_align;
>> +#endif
>> +}
>> +
>
> Why do you need to store the original alignment? Is the calculated
> alignment not enough?

I think this one can go. You are right.

>> +++ b/mm/slab.c
>> @@ -1729,6 +1729,31 @@ void __init kmem_cache_init_late(void)
>>   	 */
>>   }
>>
>> +static int __init memcg_slab_register_all(void)
>> +{
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> +	struct kmem_cache *cachep;
>> +	struct cache_sizes *sizes;
>> +
>> +	sizes = malloc_sizes;
>> +
>> +	while (sizes->cs_size != ULONG_MAX) {
>> +		if (sizes->cs_cachep)
>> +			mem_cgroup_register_cache(NULL, sizes->cs_cachep);
>> +		if (sizes->cs_dmacachep)
>> +			mem_cgroup_register_cache(NULL, sizes->cs_dmacachep);
>> +		sizes++;
>> +	}
>> +
>> +	mutex_lock(&cache_chain_mutex);
>> +	list_for_each_entry(cachep,&cache_chain, next)
>> +		mem_cgroup_register_cache(NULL, cachep);
>> +
>> +	mutex_unlock(&cache_chain_mutex);
>> +#endif /* CONFIG_CGROUP_MEM_RES_CTLR_KMEM */
>> +	return 0;
>> +}
>
> Ok this only duplicates the kmalloc arrays. Why not the others?

It does duplicate the others.

First it does a while look on the kmalloc caches, then a 
list_for_each_entry in the rest. You probably missed it.

>> @@ -2331,7 +2350,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>>   			continue;
>>   		}
>>
>> -		if (!strcmp(pc->name, name)) {
>> +		if (!memcg&&  !strcmp(pc->name, name)) {
>>   			printk(KERN_ERR
>>   			       "kmem_cache_create: duplicate cache %s\n", name);
>>   			dump_stack();
>
> This implementation means that duplicate cache detection will no longer
> work within a cgroup?

For the slab, yes. For the slub, I check to see if they belong to the 
same memcg.

That said, this can and should be fixed here too, thanks for spotting.

>> @@ -2543,7 +2564,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>>   	cachep->ctor = ctor;
>>   	cachep->name = name;
>>
>> +	if (g_cpucache_up>= FULL)
>> +		mem_cgroup_register_cache(memcg, cachep);
>
> What happens if a cgroup was active during creation of slab xxy but
> then a process running in a different cgroup uses that slab to allocate
> memory? Is it charged to the first cgroup?

I don't see this situation ever happening. kmem_cache_create, when 
called directly, will always create a global cache. It doesn't matter 
which cgroups are or aren't active at this time or any other. We create 
copies per-cgroup, but we create it lazily, when someone will touch it.

At that point, which cache will be used depend on which process is using 
it.

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