linux-kernel - Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create

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Message-ID: <52B2B0A4.8050009@parallels.com>
Date:	Thu, 19 Dec 2013 12:39:00 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Vasily Averin <vvs@...allels.com>
CC:	Michal Hocko <mhocko@...e.cz>, Glauber Costa <glommer@...il.com>,
	<linux-kernel@...r.kernel.org>, Pekka Enberg <penberg@...nel.org>,
	<linux-mm@...ck.org>, Johannes Weiner <hannes@...xchg.org>,
	<cgroups@...r.kernel.org>, Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>, <devel@...nvz.org>
Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg()

On 12/19/2013 12:17 PM, Vasily Averin wrote:
> On 12/18/2013 05:16 PM, Vladimir Davydov wrote:
>> --- a/mm/slab_common.c
>> +++ b/mm/slab_common.c
>> @@ -176,8 +176,9 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
>>  	get_online_cpus();
>>  	mutex_lock(&slab_mutex);
>>  
>> -	if (!kmem_cache_sanity_check(memcg, name, size) == 0)
>> -		goto out_locked;
>> +	err = kmem_cache_sanity_check(memcg, name, size);
>> +	if (err)
>> +		goto out_unlock;
>>  
>>  	/*
>>  	 * Some allocators will constraint the set of valid flags to a subset
> Theoretically in future kmem_cache_sanity_check() can return positive value.
> Probably it's better to check (err < 0) in caller ?

Hmm, why? What information could positive retval carry here? We have
plenty of places throughout the code where we check for (err), not
(err<0), simply because it looks clearer, e.g. look at
__kmem_cache_create() calls. If it returns a positive value one day, we
will have to parse every place where it's called. Anyway, if someone
wants to change a function behavior, he must check every place where
this function is called and fix them accordingly.

Thanks.
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