Re: + slub-fix-memcg_propagate_slab_attrs.patch added to -mm tree

[Vladimir Davydov <vdavydov@parallels.com>]

On 04/22/2014 02:30 PM, Michal Hocko wrote:
> On Fri 18-04-14 13:08:17, Andrew Morton wrote:
> [...]
>> From: Vladimir Davydov <vdavydov@parallels.com>
>> Subject: slub: fix memcg_propagate_slab_attrs
>>
>> After creating a cache for a memcg we should initialize its sysfs attrs
>> with the values from its parent.  That's what memcg_propagate_slab_attrs
>> is for.  Currently it's broken - we clearly muddled root-vs-memcg caches
>> there.  Let's fix it up.
> 
> Andrew didn't so I'll do. What is the effect of the mismatch? I am
> really drowning in that code...

If we tune a kmem cache's params via sysfs and then create a memcg that
wants to allocate from the cache, the memcg's copy of the cache will
have default values of the sysfs params instead of those of the global
cache.

> 
>> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
>> Cc: Christoph Lameter <cl@linux.com>
>> Cc: Pekka Enberg <penberg@kernel.org>
>> Cc: Michal Hocko <mhocko@suse.cz>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>
>>  mm/slub.c |   11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff -puN mm/slub.c~slub-fix-memcg_propagate_slab_attrs mm/slub.c
>> --- a/mm/slub.c~slub-fix-memcg_propagate_slab_attrs
>> +++ a/mm/slub.c
>> @@ -5071,15 +5071,18 @@ static void memcg_propagate_slab_attrs(s
>>  #ifdef CONFIG_MEMCG_KMEM
>>  	int i;
>>  	char *buffer = NULL;
>> +	struct kmem_cache *root_cache;
>>  
>> -	if (!is_root_cache(s))
>> +	if (is_root_cache(s))
>>  		return;
>>  
>> +	root_cache = s->memcg_params->root_cache;
>> +
>>  	/*
>>  	 * This mean this cache had no attribute written. Therefore, no point
>>  	 * in copying default values around
>>  	 */
>> -	if (!s->max_attr_size)
>> +	if (!root_cache->max_attr_size)
>>  		return;
>>  
>>  	for (i = 0; i < ARRAY_SIZE(slab_attrs); i++) {
>> @@ -5101,7 +5104,7 @@ static void memcg_propagate_slab_attrs(s
>>  		 */
>>  		if (buffer)
>>  			buf = buffer;
>> -		else if (s->max_attr_size < ARRAY_SIZE(mbuf))
>> +		else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf))
>>  			buf = mbuf;
>>  		else {
>>  			buffer = (char *) get_zeroed_page(GFP_KERNEL);
>> @@ -5110,7 +5113,7 @@ static void memcg_propagate_slab_attrs(s
>>  			buf = buffer;
>>  		}
>>  
>> -		attr->show(s->memcg_params->root_cache, buf);
>> +		attr->show(root_cache, buf);
>>  		attr->store(s, buf, strlen(buf));
>>  	}
>>  
>> _
>>
>> Patches currently in -mm which might be from vdavydov@parallels.com are
>>
>> slub-fix-memcg_propagate_slab_attrs.patch
>> slb-charge-slabs-to-kmemcg-explicitly.patch
>> mm-get-rid-of-__gfp_kmemcg.patch
>> mm-get-rid-of-__gfp_kmemcg-fix.patch
>> slab-document-kmalloc_order.patch
>>
> 

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