From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Enberg Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() Date: Thu, 19 Dec 2013 12:23:41 +0200 Message-ID: <52B2C92D.2020301@iki.fi> References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <52B2AB7C.1010803@parallels.com> <52B2B0A4.8050009@parallels.com> <52B2BBB4.3090209@parallels.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=message-id:date:from:mime-version:to:cc :subject:references:in-reply-to:content-type :content-transfer-encoding; s=smtpout; bh=rYbzilR4Lsvp6kmgZsHrAJ o5ugk=; b=DpCoQPSOqOd9G1WbZbYWq2AFize2NF9FmDktPyiO3Wt4ph95dvM+jO Sg6GEdAZe3jwx3rOmzXU+FimCaPSPx1oEgE9nKP7Mth8eRwE0Z0D+k4qWvztKKo/ pKwBDBWHQfQBjVgdpMH7a4P2f5P2pZcOQQrTSvOutCNlNGuV4VnqA= In-Reply-To: <52B2BBB4.3090209@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Vasily Averin , Vladimir Davydov Cc: Michal Hocko , Glauber Costa , linux-kernel@vger.kernel.org, Pekka Enberg , linux-mm@kvack.org, Johannes Weiner , cgroups@vger.kernel.org, Christoph Lameter , Andrew Morton , devel@openvz.org On 12/19/2013 11:26 AM, Vasily Averin wrote: > On 12/19/2013 12:39 PM, Vladimir Davydov wrote: >> 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. > I believe expected semantic of function -- return negative in case of error. > So correct error cheek should be (err < 0). > (err) check is semantically incorrect, and it can lead to troubles in future. I don't know what semantics you are referring to but a typical convention in mm/*.c is to return zero on success and negative on error but never positive numbers. Looking at mm/slab_common.c, "if (err)" is the established convention so using "if (err < 0)" just because is pointless here. Pekka -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753209Ab3LSKXt (ORCPT ); Thu, 19 Dec 2013 05:23:49 -0500 Received: from out2-smtp.messagingengine.com ([66.111.4.26]:52817 "EHLO out2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753062Ab3LSKXp (ORCPT ); Thu, 19 Dec 2013 05:23:45 -0500 X-Sasl-enc: iOYOlD+XjIXzYv726LlEI1kUZzZpVnu1mn+tX5fqxUx3 1387448624 Message-ID: <52B2C92D.2020301@iki.fi> Date: Thu, 19 Dec 2013 12:23:41 +0200 From: Pekka Enberg User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Vasily Averin , Vladimir Davydov CC: Michal Hocko , Glauber Costa , linux-kernel@vger.kernel.org, Pekka Enberg , linux-mm@kvack.org, Johannes Weiner , cgroups@vger.kernel.org, Christoph Lameter , Andrew Morton , devel@openvz.org Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg() References: <6f02b2d079ffd0990ae335339c803337b13ecd8c.1387372122.git.vdavydov@parallels.com> <52B2AB7C.1010803@parallels.com> <52B2B0A4.8050009@parallels.com> <52B2BBB4.3090209@parallels.com> In-Reply-To: <52B2BBB4.3090209@parallels.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/2013 11:26 AM, Vasily Averin wrote: > On 12/19/2013 12:39 PM, Vladimir Davydov wrote: >> 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. > I believe expected semantic of function -- return negative in case of error. > So correct error cheek should be (err < 0). > (err) check is semantically incorrect, and it can lead to troubles in future. I don't know what semantics you are referring to but a typical convention in mm/*.c is to return zero on success and negative on error but never positive numbers. Looking at mm/slab_common.c, "if (err)" is the established convention so using "if (err < 0)" just because is pointless here. Pekka